1999 Chevy K2500 Suburban 6.5 Diesel (Automatic)
 

(Last Updated Jan 4 2020)


Details:

1999 Chevrolet K2500 Suburban
6.5 Turbo Diesel Engine (Originally 194 HP and 430 Lb. Torque.)
4l80E Automatic Transmission
Weight (with 3rd seat removed) is roughly 6,200 Lbs.


Fluids & Filtration:

Amsoil Premium Protection 10w40 Oil.
Viscosity: 95.9 at 40c, 14.6 at 100c.

Amsoil EaO26 Oil Filter; filters to 20 microns at a 98.7% absolute capture rate.

Amsoil EaBP90 Bypass Oil Filter; filters to 2 microns at a 98.7% absolute capture rate.

Gear Oil: Amsoil Severe Gear 75w90 Synthetic.
Viscosity (as of 2019; I have oil from 2015 in my Suburban now which may differ: ) 102.4 at 40c, 15.9 at 100c.

Power Steering: Amsoil P.S.F.;
Viscosity: 33.8 at 40c, 7.5 at 100c.

ATF in Transfer Case: Amsoil OEM.
Viscosity: 36.5 at 40c, 7.5 at 100c.

Transmission rebuilt, fluid changed with part synthetic or full synthetic. I plan to change completely to Amsoil ATF if I can do so without issue.

Fuel Additives:

Opti-Lube Boost (1 oz. per 10 gallons; 100% treat rate)
Opti-Lube XL (2 oz. per 10 gallons; 80% treat rate)


Mods:

Cold Air Intake (Homemade. Could be bigger but would that help?) - Added 12 November 2015 (improved later.)
Roof Rack Delete - Removed on 23 September 2016;
Tires: General Tubeless Radial LT245/75R16; Front kept at 65 PSI Cold, rear at 80 PSI Cold.
ScanGaugeII (Version 4.13) - et at -75% (give or take.)


The car has a coolant/engine block heater which works but won't reach operating temperature. I haven't seen it get hotter than 123 Degrees F on a warm day. If the outside temperature is in the high 20s the heater can get the coolant to the mid 70s before starting. With that temperature and Shell T6 oil (which I'm not using anymore) I didn't get lots of engine rumbling on starts.

Mods done and removed:

Front (Partial) and Rear (Full) Side Skirts Made of Duct Tape: 30 December 2015 - May 2016; worked but Mom hated how it looked. I plan to do better.

I may also do these:

Other Aerodynamic Upgrades
Alternator On/Off Switch and/or removal, replacement with Deep Cycle Batteries
Oil and Transmission Heaters
Manual Transmission

(Old 2018 Pic added on Jan 4, 2020; the air dam now curves around the sides.)

https://media.discordapp.net/attachm...500&height=375

First thing I would add some coolant. The "low coolant" light comes off a sensor in the overflow tank. When it's cold most of the coolant is in the radiator, when it warms up and expands it pushes some coolant into the overflow and makes the level high enough to turn off the light. So add some more of the proper coolant (or some of the stuff designed to go with any type of coolant) to the overflow tank, there should be a cold and a hot line on the tank. Fill it to the cold line if the motor is cold or the hot line if the motor is fully warmed up. Realize this is the overflow not the actual radiator. Never take the radiator cap off when the motor is fully warmed up.

Also you should check your tire pressures cold not hot. It really doesn't matter what they get to hot it's cold pressure you want to set them at. There is a bit of a debate as to how high is ok but with a 2500 series you should have LT tires good for 75 psi cold.

I had a 1999 7.4 gas 2500 Suburban. One problem we had that apparently was a design problem with the transfer case this year Suburban and even Duramax Diesel trucks of the next few years after, was a little clip inside would vibrate and rub the inside of the transfer case until it made a BB sized hole in it. Then all the fluid would leak out and ultimately cause the expensive transfer case to fail. When mine happened luckily I noticed the leak and fixed the hole with some JB weld which held up fine.

here is a picture of where the hole will develop on the outside of the transfer case
http://www.gm-trucks.com/forums/uplo..._27_145973.jpg
until it happens it's not worth worrying about. Like I said I fixed mine with $5 worth of JB weld but they do make a kit that can go inside and permanently fix it but it has to come out and apart for that.

Some times the GM coolant level detector just turns on for no reason.
Mine would always come on, I would check it and the radiator would be full.
The 600 watt block heater is a poor excuse for a coolant heater, this is a coolant heater:
http://ecomodder.com/forum/showthrea...mer-23893.html

^ What he said. I have a 400w on my 1.0L engine and it takes several hours to make an appreciable difference.

Congratulations on your new Suburban! That is a nice vehicle.

Here are a few things I would suggest from my years of Chevy ownership.

First, if your Suburban has 4wd, it should be called a K2500 (not a C2500). This is obviously mission critical to know. [/sarcasm]

A lot of people relocate the PCM on these trucks, which stock are cooled with diesel fuel flow but are typically relocated off of the block and put on an aluminum heatsink. I would suggest you check to see if it has already been done to your Suburban or not.

I would suggest you check your radiator and condenser fins, and make sure they are not full of junk or closed up. I spent a lot of money on my 1991 Chevy K2500 because some genius pressure washed up in the front of the truck and bent over most of the fins on the AC condenser, causing it to barely overheat. My truck would lose a bit of coolant over time, which I now know was boiling off. Of course I or the multiple shops I took the truck to didn’t notice this until after the engine and tranny blew, and then I had to fix it myself when shops insisted it was ok the way it was.

Also are you checking the level of the coolant in the reservoir, or are you also checking the coolant level in the radiator? You may need to check and make sure there is not an air pocket in the top of the radiator.

I would change your tire pressures, check them cold and put the front at the same level or higher than the back. Assuming your truck has LT tires (which it should) max is probably between 65 and 80 psi. Note unless you are hauling a large amount in the back, your front is quite a bit heavier than the back due to the heavy turbo diesel powertrain. I typically run my front tires 0-5 psi higher in pressure than the back tires, to get more even wear.

The single best FE improvement I made to my gas 1991 K2500 was swapping the 4L60 Auto Transmission out for a NV4500 Manual Transmission. I know you may not want to do that right now, but it would be something to keep in mind.

One thing I do whenever I get a new to me vehicle is change all the fluids myself. You never know what sort of junk the prior owner poured into them, or if they even checked them. I would suggest you change the transmission fluid yourself manually, and would suggest avoiding shops that use a pressurized flow to flush out the old fluid, as these are known to destroy transmissions. I would also suggest changing out the fluid in your front and rear differentials and your transfer case. There is a lot of fluid churning about on cold starts, so I would suggest using low viscosity synthetics of the appropriate specification.

The excess reservoir has a radiator type cap on it, though. Would Prestone coolant work?

I'll have to check the tires. They say "80 PSI max" though and for reference, the ratings on the driver's door say "55 front, 80 rear".

Ooh, Valuable information. Thanks.

There's more I'd like to reply to but it'll have to wait. I did read it though.

I say drain and flush the cooling system to prevent mixing of dexicool and regular antifreeze and creating black cooling system sludge.

Is it not a bit early to do that given the weather here in Pennsylvania? What should I do?

Congrats on the new diesel.

I had a 83 K2500 diesel pickup for 17 years and 305,000 miles, so have some insight into this vehicle.

Buying a used 6.5 my first advice is to have the engine, radiator, and heater professionally acid-cleaned and back-flushed. these engines are touchy about being over-heated. I'd still have that old 6.2 but the engine got hot and cracked the block at the No. 8 cylinder.


I completely agree with Post #8:
"The single best FE improvement I made to my gas 1991 K2500 was swapping the 4L60 Auto Transmission out for a NV4500 Manual Transmission. I know you may not want to do that right now, but it would be something to keep in mind."

That a minimum 2 MPG improvement just waiting to happen. Further, and maybe more importantly, you'll be ditching a transmission that was never intended to be used with a diesel. Even the 6.5 makes a lot of torque at low RPM. so much so that the torque converter cannot pump enough fluid to keep the transmission cool. A cooler does not help. Fluid flow is simply inadequate. My old 6.2 had a 700 R4 and later a TH400 and I trashed them seven times. Spectacular failures - scattering parts an fluid down the road. Lots of plastic parts obviously melted and ferrous metal parts turned blue. The stick completely eliminates this problem. The conversion is old hat in the Chevy pickup/Suburban community.

There are uncorroborated stories out of GM about a 6.2 suburban with 2.73 gears that could get 30 MPG. I don't see why you couldn't get 23-25 with some modest effort.


Here is your gold mine for 6.5 information.

The Diesel Page - for the 6.2L, 6.5L, and Duramax 6600 (6.6L) GM Chevrolet and GMC diesel engines.

They've been at this for nearly two decades.

That's a nice rig. BTW one guy at 4BTswaps claimed to have had some good fuel-savings improvement by replacing the engine-driven cooling fan by a dual-fan setup out of some Chevy minivan with dual-zone air-conditioner.

Thanks, I'll have to keep an eye out for that.

Honestly, the coolant does seem to be low as it is now even hot. Maybe we'll have to call the previous owner and ask what coolant he was using. I read in the (mostly gasoline related) manual that it should use DexCool and an employee at AutoZone told me the same, but just in case...

I'm not sure what kind of wattage the current heater is. I have to fix or get the cable fixed though, one of the wires in it just frayed. But I may change the heater and add more heaters to it, Diesel Dave style.

Yeehaw, Thanks! (And while anyone else is reading who contributed, Thanks to you too.)

Where could I get the radiator, heater and engine acid-cleaned and back-flushed? Pittsburgh isn't too far of a drive for me.

I may change the transmission eventually, but for now the automatic one is staying.

Also, This vehicle is going to be towing things like a 4,700-5,400 pound car + trailer so I'm not going to change the gears in the rear. I'll be changing the differential fluid, though.

And so far, the vehicle has a roof-rack on it and I'm not sure if I can remove it or not.

Thanks, I may get an electrical fan though which I understand is supposed to get even higher MPG since it's not on all the time.

On subject of fluids!

What full synthetic differential fluid could I use? And what full synthetic ATF could I use? I was looking at Mobil-1 for the Differential Fluid, and for a while I was thinking of some Mobil-1 for the ATF as well but I'm not sure it will work.

The subject of fluids will get you a wide array of opinions. I would suggest determining the OEM specification, and sticking to a fluid of that specification (unless you have a good reason not to) from a reputable brand. There are many high quality fluids brands out there, and I don’t really think any of them are truly significantly better than the others, so long as you are using the correct spec.

Me personally, for the engine I run Mobil 1 engine oil with a Wix oil filter for convenience of local purchase. For everything else, (differentials, transmission, transfer case) that doesn’t get changed often I get Amsoil fluids. Two of the biggest reasons I run Amsoil are that I like that Amsoil’s website gives you the specifications and amounts for your vehicle and that they tell you the viscosities of their fluids at different temperatures.

If you don’t already, definitely get a hand held oil transfer pump for adding the fluid to the differentials and transfer case.

Just in case you run into this, on my old truck the fluid I took out of the rear differential was nasty. It must have gotten water in it. If I put my good fluid right in, there would have been a lot of that mess in my new fluid. I wiped out as much as I could, but then to help “clean” the differential out, I filled it up with some engine oil (cheaper and I had it) and drove it around like that for a bit. Then when I re-drained the fluid the second time, it got most all the junk out so my good fluid wouldn’t be full of junk.

Makes sense. Though I do recall there's a thread on here where someone said "I think the instruction manual for this car states too thick of a differential fluid for this car" I'll just stick with 80w90 for now, differential wise.

The oil pump is a good idea, thanks. I didn't think of it.

I can understand about flushing out a system... My father used to do that with oil changes in the 1970s, but that was before oil got to be a lot thinner (to my knowledge.)

Re: Post #13

“Where could I get the radiator, heater and engine acid-cleaned and back-flushed? Pittsburgh isn't too far of a drive for me.”

Big Dave says;
I’m sure there is someone in Pittsburgh that can do it. I found a local radiator shop in suburban Naptown to do the job. Pittsburgh should be no different.

Depending on how long you can live with the truck down, pull the water pump off and give it a good looking-over. The water pumps on these trucks are integral to the block and are pricey. Ask me how I know. You really don’t want to run acid through the water pump if you can help it. Delime it by hand if you can.

Borescope your radiator. If it is badly limed up or corroded, think about a replacement. These are volume-built radiators and in the scheme of things, not all that expensive. Your water pump probably costs twice what a radiator costs.

If the radiator is merely corroded, a regular acid back-flush will add years to the service life, but if it is limed up you need to get drastic. If the radiator is limed up you can bet the farm that the block and heads are limed up and lime isn’t easy to remove. Citric acid won’t touch it. Rig up a pump setup and pump muriatic acid (swimming pool concentration – the stuff used for cleaning masonry is too strong) through it. Let it run a minimum of three days. A week is better. Lime is that tough. Then neutralize it with a solution of baking soda and distilled water. Back flush again with tap water, then with distilled water. At that point you’ve done all you can.

Just to show the extremes: My Ford uses an International 444E engine. Very tough engine still in wide use for school buses (which is savage duty for an engine.) It uses a very powerful (and expensive) water pump. So powerful that the high flow through the block would cavitate and pit through the first two water jackets. Seems amazing but I have seen such damaged engines myself. Ford pickup used to have to add an additive every three months or so to suppress the cavitiation. To fight this I switched tio waterless coolant. But I had to back flush and then completely dry the engine. That is major operation when you have a big engine in a tight engine compartment. And the waterless coolant is $40 a gallon. But it is the last stuff I ever have to put in it. Best of all: after six years of complete neglect I have zero cavitation pitting, zero corrosion, and zero lime. Bright metal looking back at me. You probably don’t want to get that radical. I drive a lot and expect at least 600,000 miles out of my engine and transmission. At least it won’t die from heat.



“I may change the transmission eventually, but for now the automatic one is staying.”

Big Dave says:
It’ll let you know when it’s time to change. Pieces scattered down the road are a cogent argument. Make a plan to convert and execute it when the automatic grenades itself.

Oh say, can you see a brown or black dump that was in the tranny?

http://i50.photobucket.com/albums/f3...pshuqkbaf6.jpg

Yeah, that was in the transmission pan. I replaced the filter and fluid but will need to change the fluid at least two more times before it's clean enough for me. On the first of two fluid changes I may put some Seafoam Trans-Tune in.

The fluid went without being changed so long that even the plastic on the dipstick stinks. At least the lever shifts easier now.

I suggest going here and do some reading:
6.2 and 6.5 Diesel Engines | The Truck Stop
I am a member there also.
I have a 96 and 93 6.5 diesel. am fixing the 96 up for sale but will be keeping the 93.
I installed a Gearvendors OD unit, have the auto and 4.10 gears. at 65 I am at 2000 rpm, which is the ideal rpm for these engines.
I plan on putting a short bed and to shorten the frame and I want to put in a 5 speed and 12 valve Cummins.

Update: I got the first fuel economy reading: 12.09. However, that's with a leaky fuel injector on part of the tank and with cold weather and usually a bit of idling to prevent engine damage.

I'm still replacing the transmission fluid with some Valvoline Full Synthetic. ($16.97 per gallon at a nearby Walmart.) The fluid has been getting cleaner with every time I replaced it in the pan, though even after three changes it was still brown. Is it a 12.5 quart system? I read somewhere that it is. I used to have a difficult time just moving the transmission lever which got easier after changing the fluid in the pan just once.

I also have the ScanGaugeII plugged in to it and the pre-heater (if it's working; it seems to work) is used before I start up the vehicle. I'm not sure what the heater goes to though - if it goes to the engine coolant it doesn't work (no difference in temperature.) But maybe it goes to the oil pan?

Sub 15mpg is pretty normal for 90s 2wd 6.5L suburban.
I believe they come with 4L80E transmission, which isn't super efficient and they tend to have 3.73 or 4.10 gears.
Check out dieselplace dot com.

I say if you are using trying to flush the transmission get a pan with a drain plug and use the cheap fluid that is only about $10 a gallon.

The coolant heater is in the water jacket, if its working, after you plug it in you should start to hear a crackling, sizzling or hissing sound from the water in contact with the element boiling. If its quiet and not sparking when you unplug it its likely dead.

I was looking up Differential Fluids and Autozone's computer suggests 80w90. But is there any problem with running 75w90? I saw some nice Mobil-1 Full Synthetic in there which I was thinking of using.

I put mobil1 synthetic in the diff of my half ton suburban back in 2008 or 2009 and have not had any issues.
I will most likely put that same oil in the 10.5 inch 14 bolt diff on the C2500 I just picked up.

When changing the diff fluid I recommend putting the cheap stuff in there running around on it for a day or 2 then keep changing it every few days until it becomes clear. On that first change take something like WD40 (not brake cleaner) and spray out the bottom of the diff, that is where all the metal shavings and gunk are going to collect. If you clean the bottom of the diff it should only take one flush to get it cleaned out.
Also wear gloves and use safety glasses.

If the transmission looked like it was filled with used motor oil then the rear diff will likely look about the same or worse.

I didn't mention this earlier, but we had the reverse go out. (Edit - That's why I posted about the ATF being black.) So, $1,050 later the thing is back on the road working with not just the band fixed but the mechanic also worked on another band which needed work and flushed the transmission, transmission cooler and torque converter. The vehicle coasts longer now.

Now I'm working on the power steering system, changing the fluid. The old stuff was junk and smelled burnt.

I hope that resolved your transmission issues. You may want to check that your ac condenser, radiator, intercooler, (anything in the front air is supposed to flow through) is not clogged or stopped up causing the transmission to overheat due to inadequate flow through the cooler. I now know that was the reason I had many many transmission issues in my 91 Chevy K2500.

X2.
money well spent but a nightmare nonetheless.

Thanks, though he did flush the transmission cooler. And the transmission is working a lot better than it was, unless I'm missing something.

In other news, I flushed the power steering. I changed the fluid in the reservoir several times yesterday, and after that I put almost three full cans of Seafoam Trans-Tune through it. The old P.S. fluid was black and not very effective; The new fluid is not quite 100% clear but I can see through it a whole lot better than the old stuff.

I wasn't referring to the tubes (liquid passages) being open, but the fins (air passages) through the front. If they are crushed or constricted, they can prevent airflow, which will make your transmission overheat, fluids turn dark, and ultimate failure. Since you had transmission issues that included dark fluid and since your power steering fluid is also dark, I would check this.

Backstory:
Some genius pressure washed the front of my old 1991 Chevy k2500 before I owned it, which folded over all the fins of the AC condenser, seriously restricting the airflow through the radiator and transmission cooler. Me, not knowing much about cars at the time, repeatedly took the truck to the shop for various engine and transmission issues, which I now know were symptoms of the AC condenser problem. Many thousands of dollars later, I finally figured out the actual problem on my own, no thanks to any of the many mechanics who had seen the truck, removed the AC condenser and all the issues went away. If I had replaced the AC condenser with a new one the day I bought the truck, I would not have had any of the issues I did. That is why I suggest checking the fins of your AC condenser, radiator, etcetera and make sure air can flow through and that they are not clogged.

Oh. I'll do that, thanks. I'm not sure if it's that or if one or more previous owners just neglected to change fluids.

I changed the rear Differential oil. I couldn't get one of the bolts off so the "Pumpkin" plate stayed on. I may be changing it more than I thought because of that. The old oil looked like used engine oil, but it was not like the Transmission fluid.

On another subject, while I was working on the car I heard a racket outside on the street. Someone was driving a vehicle which looked like a Suburban; He/she went by and the car was squeaking and there was some sort of overheating going on which didn't come from the tailpipe (it wasn't burning oil) so I wonder if it was a stuck brake or if he was cooking his differential. It would be a bit funny if it was the rear differential out of oil, considering what I was doing. It slowed down and stopped as the car did, so I don't think it was a lack of engine coolant.

Changing the front differential oil was easy, as there was a drain plug.

Gear oil changed with Amsoil 75w90 Severe Gear and I have an appointment for the tires to be aligned on the 21st. I will say that I can see why Diesel Dave gets such high fuel economy out of his truck, I'm sure that if I had an opportunity to do a fuel economy run then I could get this to go over 30 AVG on the Scangauge once warmed up.

every time i see my 93, 4 door, 6.5, AT with GV OD, I want to drive it. it has sat for 3 yrs now. went through 3 "sets"(6 batteries!) of batteries because 'i was gonna drive it once a week to keep it in shape', but it never happened. wants are to swap a Cummins, either 3.9 4BT or 12 valve. i miss that truck!

Sure a Cummins is great, but the old Chevy Diesel V8 still has its value. Being IDI, it's more tollerant to experiences with vegetable oils as an alternative fuel :thumbup:

Tires are aligned. Now I can actually drive it in good confidence.

I also have a fuel tank leak near the top of the tank... It's somewhere in the top quarter of the tank, I think. It stopped leaking after I went 180-200 miles.

Been driving it and enjoying it, surprisingly. As for plans:

POR-15 (Rust Prevention Coating)
Front Air Dam
Rear Wheel Arch Covers
Partial Front Wheel Arch Covers
Oil Pan, Transmission Pan and Fuel System Pre-Heaters (The last one's for winter use)
Amsoil Oil Bypass Filtration System (I'm not sure this will increase MPGs, though it'll keep the oil cleaner if it works as advertised.)
Power Steering Fluid Flush (The first flush didn't clear out all the brown burnt fluid. It did help though, and I imagine may increase MPGs a bit if old fluid has been putting extra strain on the system.)

Can this vehicle run on 100% Biodiesel without modifications? I realize that may plug up the fuel filter if I do it all too quickly, since Biodiesel loosens unburnt petrol fuel.

I'm also wondering if I should put in a filtration kit for the engine coolant. Does that increase MPGs? I was reading the sites that sell those kits say there's something leftover from the manufacturing process of a Diesel engine and a filtration kit can remove that.

Are there instructions on here about keeping the SG2 on while EOCing with a manual transmission?

I experimented with coolant filters several years ago, back around 2008 I don't think they are worth the money, time and effort.

I do not know if that DB4 injector pump will run straight biodiesel with out any trouble. A mechanical DB2 injector pump will.

Thanks. Did I mention I stuck some of this Rislone 3x ZDDP Additive to the engine oil?

http://shop.advanceautoparts.com/wcs...5_pri_larg.jpg

Shortly after that (this has been weeks by now) I started using a Biodiesel blend (Sticker at the pump says "Between 5% and 20%") and the engine sounds like it's running smoother; I'm not sure why it is though, if it's the additive or the fuel. Nifty though and I like the fuel. I also read that Biodiesel works as a solvent and will loosen unburnt fuel which (in some cases) clogs a fuel filter - though the quickest way to find out would be to use 100% if the system works that way.

Oh, I also didn't mention this earlier; there's a rust spot (really, it's all the way through) just above the tailpipe. That has to be repaired and I have the metal piece needed, thankfully.

I am not sure about that crappy computerized pump will like b100. I do know your fuel hoses need to be replaced. I just replaced my 1/8" jumper return hoses about 6 months ago. I still have a mechanical fuel lift pump but I am only running b20.