Disappearing Engine Coolant

[MrMark52]

‘02 Workhorse W22 with the 8.1l engine. About to turn 50k miles.

Confirmed radiator was topped off through the radiator cap before filling empty coolant reservoir last week - prior to a drive from basically Dallas to Little Rock to Durant, OK and back to Dallas (left Monday, returned Friday).

Looking yesterday, coolant reservoir is empty again. No sign of coolant leaking to the ground at any of the 2 night stops made in AR or OK.

The overflow hose between the radiator and reservoir did come loose a few months ago and drain the reservoir and I fixed that, then topped off and refilled the reservoir.

Engine runs good and runs good cool. After all the work I’ve done to insure it’s running properly (replaced failed fuel pressure dampener, did the ECM/TCM upgrade, and monitor fuel trims), mpg mileage seems to improve with every trip (we’re seeing 7.5-7.6 mpg without our toad).

No visible sign of coolant contamination in the engine oil although I do need to look at the transmission fluid.

Could there be a coolant bubble in the system and it’s just slow to work out?

Is there a chance I’ve got a leaky head or intake manifold gasket? Not looking forward to tearing into the engine blindly.

[Steverino]

Not an expert in this, but I believe there's a test you can do for exhaust / combustion gasses in your coolant. That might help you narrow it down...

[propchef]

Originally Posted by Steverino

Not an expert in this, but I believe there's a test you can do for exhaust / combustion gasses in your coolant. That might help you narrow it down...

https://www.blackstone-labs.com/prod...ree-test-kits/

For testing the oil for contaminants, including coolant.

A bad head gasket can cause this. Has the engine ever overheated?

Does this system require bleeding? If it does you may have a stubborn bubble. I had a German car that I had to replace the cooling system every 60k miles. It required bleeding and it was always a pain, taking a few tried to get all of the air out.

A pressure test can tell you if you have a leak as well. You can borrow these at AutoZone and O-Reilly's

[Fotoryder]

Auto parts stores will have test kits to detect exhaust gas in coolant. Some use test trips, others draw a sample of coolant and add a chemical.
Also check your overflow tank while the engine is at operating temperature and running to se if it blowing out coolant.

[donr103]

From inside rv.. open engine hatch.. get very strong flashlight.. inspect rear, top of engine.. closely inspect intake manifold for any signs of leaks.. check hoses .. each one that goes to radiator.. from inside.. you may have to use your cellphone with flash on and record.. in tight engine compartment.. watch vids.. look for leaks.. under hood.. find the evap drain to dash a/c.. put figure in hole.. see if sign of antifreeze.. my rv is 7.4l had leak at rear of intake and no signs of dipping.. because hot coolant would run down back of engine and evaporated before one could see it.. found tell tell signs of antifreeze running down back.. report back and better opinions will follow .. does the radiator coolant resovior bubble when engine running ?
Good luck and keep us posted

[House Husband]

Check the torque on the intake manifold bolts.
That engine type has been known for coolant leaks at the intake manifold.
Coolant can be seeping into #1 & #2 intake ports.

Richard

[jrugarber]

I had a similar issue with my coolant, topping off the surge tank only to see the level drop and refilling again, after envisioning every worst case scenario it was recommended to try the cheapest and easiest fix first. My original cap (picture) is circled in red, missing the large rubber gasket, the new replacement cap circled in green, has a large rubber gasket that seals against the edge of the surge tank.
My coolant has stayed at the proper level through 2,700 miles, at ~ $35.00 it was worth a shot and hopefully it has solved the issue.

[ArtJoyce]

its not always a leak. Sometimes when you lose coolest like you did with the disconnected hose. it's takes awhile to get it full. It's not just fill it back up, but you have to run several hot/cool down cycles to burp out air that is in the system.

[David 70]

My 7.4 was doing the same thing. I was getting antifreeze in the oil. Just checking the dipstick or changing the oil when hot showed nothing. In order to check for coolant in the oil for sure you need to just crack the drain plug after it has sat at least overnight and see if there is coolant on the bottom of the pan. Mine ended up being the intake gasket. These things use plastic gaskets and they shrink from the heat. I did pull the heads and had them checked just to make sure.

[Tha_Rooster]

Do you smell any antifreeze?

[tmw188]

On my last mh W24 and the 8.3 I had a very small seepage way the t-stat housing. Replaced the gasket but still wasn’t sure if that was it. Oil analysis showed no coolant. I would try the exhaust test but not sure how accurate that is. Follow those instructions closely.

[TandW]

The coolant crossover pipe may be seeping when cooling after a shutdown while there is still pressure and it is cooling down. Hot fluid drying off of hot metal and hitting the air will smell sickening sweet. The leak may not hit the ground, let alone any lower parts before the system goes into vacuum while cooling further. Check for "washing" of engine grime around and beneath the flange connections on the heads. Expansion and contraction is the culprit.

[MrMark52]

Thanks all so far for your input!

To answer a few questions -

There is no indication of the radiator pressurizing from exhaust pressure in the coolant system as would happen with head gasket blow-by.

No “sweet” smell of anti-freeze.

I do not know of the engines history prior to 37k miles - but the engine is clean, no sign of either exhaust manifold loosening or breaking as maybe the result of overheating.
I will say a PO at some point had a serpentine belt failure as I found a piece of the old belt still tangled behind the pulley’s when I replaced the idler’s and belt earlier this year.

I didn’t see anything unusual on the plugs when I changed 06/21 after we had put maybe 1000 miles on the coach (this is just an FYI as the coolant loss issue if it’s really being lost and burned in the engine to be burned might would have been evident here. I suspect these were the OEM plugs that had also been experiencing the affects of a failed fuel dampener - for how long, who knows).



I’ll pull the doghouse tomorrow and start snooping around for signs of dried coolant after topping the coolant off again and going for a drive.

[tmw188]

Check all clamps with a nut driver. Small bypass hose near t-stat?