1999 Chevy K2500 Suburban 6.5 Diesel (Automatic)

[101Volts]

(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.)

[Hersbird]

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.

[Hersbird]

here is a picture of where the hole will develop on the outside of the transfer case

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.

[oil pan 4]

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

[Ecky]

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

[aardvarcus]

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.

[101Volts]

Originally Posted by Hersbird

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.

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

Originally Posted by Hersbird

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'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".

Originally Posted by Hersbird

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.

Ooh, Valuable information. Thanks.

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

[oil pan 4]

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

[101Volts]

Originally Posted by oil pan 4

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?

[Big Dave]

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.