Head Gasket Diagnosis Question

[JHZR2]

Was in another thread, pulled it as it's a worthy question on its own:

Originally Posted by andyd
Chris, a car comes in on a wrecker with an obviously blown head gasket. A newish car, worth fixing .How do you figure out whether it was a head gasket failure causing the overheat, or if another leak caused the overheat and that blew the head gasket? TIA

 

[kc8adu]

i would fill the system with water and see if there are leaks/failures beyond the gasket.
also test the thermostat.
and check fan and water pump for proper operation.
in my experience barring design/material flaws a head gasket failure is almost always the result of overheating or occasionally corrosion from bad maintenance.

 

[eljefino]

Well some cars are known gasket blowers. The dodge 2.2/2.5s. The 7MGE Celica/ Cressida.

But this is 25 year old info. The context of the question given, is, is a new-ish car without a reputation yet defective in design, and how do we know?

My newest car ever, an 07 HHR, dinged at me when its radiator fan seized and the engine hit 240'F. I took immediate action, ran the heat, and pulled out of traffic for some ram-air action. Car survived and would not have had it not been dinger-equipped. I anticipate most new cars have an obvious overheat alert (vs a 1.25" gauge silently reading in the red). That said, if the driver can stop an overheat while there's still pressurized liquid protecting things, they have a pretty good shot of saving the engine.

I agree with the fill with water idea. It won't wreck the main bearings as badly if it gets in there. It'll show the mechanic how fast it heats up (air and exhaust bubbles speeding the process) and it'll show if the car stabilizes at thermostat temp or just keeps going.

 

[mk378]

If the driver kept driving overheated until she would go no more, the whole engine is toast.

 

[Trav]

You have to fix the HG in order to test the system but you can inspect a few of the more common causes of overheating.
Radiator, hoses, stuck closed thermostat and water pump impeller can all be checked without running the engine.

 

[Chris142]

Headgaskets usually get blown because the engine got low on coolant and overheated. Many of the ones I see gave plenty of warning and the owner ignored the warnings.

Adding water daily because the radiator is leaking is the most common one we see. Others did spring a leak while driving, the driver saw the gauge go up but continued to keep driving it until it seized.

 

[Lubener]

High pressure combustion gases many times will find a way to force coolant out towards the coolant bottle resulting in it filling up or overflowing.

 

[Audios]

Easiest way Ive found is to let the car sit overnight and cold start it for a few days, watch any symptoms. After, take the rpessure tested for the cooling system and pump it to 15 psi, let it sit, watch for leaks, and do a few cold starts at 15 psi. If theres a change with smoke or rough start, theres a gasket issue. Let the pressure drop to 0 and leave it hooked up. Start the car and watch the gauge for pressure too early, or if it develops too much right away. Sometiems it wont be obvious. My X3 would only show its face during a hot restart, I had a rough idle for about 4-5 seconds and then it would be fine, even overnight.