Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - 1999 Chevy K2500 Suburban 6.5 Diesel (Automatic)

aardvarcus · 02-27-2015, 07:20 AM

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.

02-27-2015, 07:20 AM	#6 (permalink)
aardvarcus Master EcoModder Join Date: Apr 2012 Location: Evensville, TN Posts: 676 Deep Blue - '94 GMC Suburban K2500 SLE 90 day: 23.75 mpg (US) Griffin (T4R) - '99 Toyota 4Runner SR5 90 day: 25.43 mpg (US) Thanks: 237 Thanked 580 Times in 322 Posts	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.