No radiator cap on 1996 6.5L. How to drain and how to fill

Angelo · Oct 16, 2020

Probably a dumb question. I read that this must be a fully pressurized cooling system since there is no radiator cap on either side, only at the overflow reservoir.

What would be the procedure to refill with coolant? I see a bleeder valve at the top of the radiator hose. Do I turn out the bleeder while filling at the overflow reservoir? Do it while the engine is running or off? Do I fill at the bleeder valve and the reservoir?

And it's obv too late now, but may be helpful in the future for myself, or for someone else with same engine, but how would you drain this system without having access to the radiator? Would you just pull off a hose on the bottom to drain it?

I pumped a half gallon out of overflow reservoir but that wasn't enough so I got coolant everywhere when I pulled off that top radiator hose to replace the thermostat. Currently waiting for the new thermostat to arrive, hopefully nothing will be damaged by the coolant sitting on the engine.

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smdk2500 · Oct 16, 2020

I just filled my 6.5 after a heater core replacement and how I did it was filled the system till the overflow was full started the truck and opened the bleeder on the t-stat housing. I don't know for sure how you drain the radiator since I havent done that yet to mine. But there are drains on both sides of the block you can take out and will get all the coolant out.

Also as a side note the module you have bolted to the intake is called a pmd. It would be a wise idea to mount it to the inside of the front bumper behind the license plate. That module is what controls the injecton pump and can cause some major problems. It doesn't like heat. Inside the bumper allows a more stable temp then in the engine compartment. The biggest problem with them is heat soak. In the engine compartment they will sit and bake till the engine cools down. For more info you might try this site
https://www.dieselplace.com/forums/6-5l-diesel-engine.21/ there are alot of knowable people over there.

Schurkey · Oct 19, 2020

There's no draincock at the bottom of the rad?

Turbokat · Oct 19, 2020

Just fill up the reservoir until its full, then start the engine and turn the bleed screw until water starts coming out of it. When i used to drain my radiator i just disconnected the lower rad hose. I tried to use the normal drain but it was seized so damn hard and the stream went everywhere so it was pretty much impossible to get it in a container so i gave up on that

Angelo · Oct 19, 2020

Turbokat said:
Just fill up the reservoir until its full, then start the engine and turn the bleed screw until water starts coming out of it. When i used to drain my radiator i just disconnected the lower rad hose. I tried to use the normal drain but it was seized so damn hard and the stream went everywhere so it was pretty much impossible to get it in a container so i gave up on that

This works! The bleeder had corrosion on it so make sure you can back it out before starting this process. I found the same as described above in this page which also goes over flushing. https://www.dieselhub.com/maintenance/6.5-diesel-coolant-flush.html

Angelo · Oct 19, 2020

smdk2500 said:
I just filled my 6.5 after a heater core replacement and how I did it was filled the system till the overflow was full started the truck and opened the bleeder on the t-stat housing. I don't know for sure how you drain the radiator since I havent done that yet to mine. But there are drains on both sides of the block you can take out and will get all the coolant out.

Also as a side note the module you have bolted to the intake is called a pmd. It would be a wise idea to mount it to the inside of the front bumper behind the license plate. That module is what controls the injecton pump and can cause some major problems. It doesn't like heat. Inside the bumper allows a more stable temp then in the engine compartment. The biggest problem with them is heat soak. In the engine compartment they will sit and bake till the engine cools down. For more info you might try this site
https://www.dieselplace.com/forums/6-5l-diesel-engine.21/ there are alot of knowable people over there.

Thanks for stressing the re relocation of the PMD. I thought it'd be fine with the heat sink there but I'm reading more and more people saying to move it to inside the bumber.
The fill process you described, opening the bleeder on t-stat housing is the way. I'll refer back here when I flush the system later this year.

jdla140 · Oct 19, 2020

Removing a radiator hose is the only way to drain coolant on a 6.2/6.5. There are drain plugs in the block, but they are behind the motor mounts so they are basically useless.

GM Guy · Oct 27, 2020

Lower left corner of the radiator is where the drain **** is. either take radiator loose in its mounts and **** it back slightly or wash out the core support prior and tilt it to the left, and collect it out the drain hole out by the fender.

Now is a perfect time to remove the radiator for proper cleaning. You cant really clean these well in the truck.

Put it on sawhorses, straighten bent find, and blow and wash and repeat till you can see through every fin.

Pull grille and do the same to the a/c condenser while radiator is out. leave condenser in truck.

As far as your thermostats, make sure and use OE grade ACDelco. 6.5Ls are picky AF about thermostats. Dont get cheap. I have a one owner 78K miled 6.5L that we bought that had puffy blowby, changed t-stats and both were broke off their flanges, had "China" stamped in there,and so I suspect she got hot and scuffed a piston. DO NOT use cheap thermostats in a 6.5!!!

Once done and back together, fill surge tank, engine off, and open bleed screw on thermostat housing. after bled, top off, squeeze upper hose a few times to burp any extra air out, and give it a whirl.

Also, while radiator is out for cleaning, perfect time to inspect harmonic balancer and pulley damper. these things are relatively hard on the HB, inspect for movement, bulging rubber, etc. and replace at the first sign of failure, or crank breakage might be in your future.

No radiator cap on 1996 6.5L. How to drain and how to fill

Angelo

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