Guys, I’m afraid my friend’s ’04 Discovery has a head gasket that has failed. With the engine running, coolant spews out the overflow pipe. Once the engine is shut off coolant drains out of the expansion tank, about 2/3 of the volume I estimate. This is after bleeding the cooling system, filling it, and driving only 10-15 minutes. I have never seen or read about anything quite like this.


The only cause I can think of for these symptoms is a head gasket failure allowing combustion gasses to pressurize the cooling system causing the overflow. Have any of you seen these symptoms?

 

Happened to me before, and a simple expansion tank cap was all it was. Advance auto had them in stock for like $15. Try that first and cross fingers.

 

If that is not the fix, a chemical test will let you know if combustion gas is getting into the system. About $50 from parts store, changes color. Could be head gasket. Could be cracked block.

 

I should have mentioned that we tried swapping the cap from my truck and the problem recurred. The truck seemed to be running fine otherwise. Of course my cap may be getting weak too. It's the original cap now 14 years old.

BTW his Scangauge showed operating temps from 205-211 vs. the 194-198 typical on my truck.

 

Try a new cap

Other than HG, a cracked block behind a sleeve can do this in short order as engine warms up, hoses become rock hard, etc.

We would hope that serpantine belt is correctly routed so water pump runs as it should. Hope thermsotat is opening up.

The normal DIY on HGs is two weekends wrenching, and take heads to the machine shop inbetween. Either have them checked or have them machines. The warp limit is 0.002 inch, or about half the thickness of your printer paper.

 

My expansion tank hair line crack at the neck between the inlet fitting and the over flow outlet. Inlet coolant would go out the over flow.

 

Come to think of it, before going out and buying caps and tanks there is an easier test. Fill the expansion tank to the brim with distilled water or coolant. Leave the cap off and start it cold. Maintain the level at the brim and rev it slightly as it warms up. Watch the fluid for bubbles. One or two small bubbles is probably nothing, but if it bubbles constantly, it's a HG, cracked block etc. If it does no bubbling, then you can smile and proceed with cap and/or tank. If it is bubbles, you can rent a sniff tester from autozone for free to confirm exhaust gases. Oh and obviously dump the excess fluid out when done.

 

Thanks for the suggestions guys. I especially like MC04DII's suggestion.

We replaced the headgaskets in my friend's garage three years ago this week, so we're praying its not a headgasket (or worse). Serp belt hasn't been messed with.

If there are no bubbles and a new cap doesn't solve the problem I have my old thermostat that I replaced 2½ years ago when we did my headgaskets. It seemed to be working okay at the time so we could try swapping it in before just buying one. If that seems to cure it I will strongly suggest he go with a 180 soft spring version permanently.

It may be this weekend before I have anything further to report.

 

Here's the update, guys, and hopefully the end of this issue. Looks like the new reservoir cap is all that was needed. My friend did the bubble test that MC04DII suggested and the results were negative. His daughter has been driving the truck to school this week week with no problems.

Now if we could just figure out why his truck runs hotter than others (205°-215°) despite a new radiator and a new thermostat and water pump (installed ~6 months ago).

 

Change to a new 180F stat and never look back.

Of course, could be sensor out of spec or partial ground (skinned wire rub) on it. Your scanner will show coolant temp, which should be close to garage ambient after overnight parking.

If tiny holes in the top leg of the stat are plugged up with trash from other work or flushing it will skew the temps higher.