new radiator cap, engine overheated

[wolfweb]

My mechanic replaced the radiator cap on my subaru forester 2003 xs saying the radiator failed a pressure test and seemed to be losing coolant somewhere. Another pressure test after the new cap was fitted succeeded. Next day after a 30 min drive, soon after stopping at my gate, the temp went into red, radiator has boiled, steam coming out of cap and fluid sprayed over engine. I immediately turned off the engine. I never had trouble with overheating before the new radiator cap. What
could have caused that? Could the overheating have now damaged the engine?

[idosubaru]

why was the car at the mechanic?

why did he test the pressure system - was he working/repairing/diagnosing something else?
 

*** ask him EXACTLY what he means by

M seemed to be losing coolant somewhere.

 

there are two ways to quickly kill an engine - overheating and lack of oil.  those are about the only two things you should never, ever do if you don't like huge repair bills or rendering a vehicle worthless.  so yes, it could have. if it barely got hot and you shut it off - no big deal. 

 

if it was hot and driven that way for a while then there's no way to know the extent without costing thousands of dollars to tear down the block at which point you might as well rebuild the engine, the cost would be nearly the similar to test verses rebuild.  if there's damage you won't know it until years from now, it won't be anything imminent (assuming you didn't run it for hours until it stopped running on it's own).  turn the A/C off, the heat on high to dump additional heat, and shut the engine off sooner next time.

 

if the engine is loosing coolant then the cooling system may need purged of air bubbles.  these engines typically overheat without a proper burping sequence for the coolant.

[idosubaru]

Also the nonturbo EJ25's in those vehicles require Subaru's Coolant Conditioner to mitigate headgasket leaks so be sure to add that if coolant has been changed or sufficient amounts lost.

[Fairtax4me]

Also wondering why the car was at the mechanic to begin with. Was it there because of a cooling system problem or did the mechanic just "find" this issue while it was there for other work?

Who was the mechanic? Dealer? Independent shop? Do they specialize in Subaru or just general auto?

 

If this was a 98 model engine I would say its probably trashed, but the 2.5 got beefed up a bit in 99 and is less prone to damage from overheating. Still, repeated overheating is the leading killer of Subaru engines. If it overheated one time you may have dodged a bullet, but don't let it happen again.

 

Either the fluid level got low again, or the cap the mechanic put on is faulty or not to spec.

 

You can get a good idea of any internal damage that was done by getting an oil sample analysis done. Blackstone Labs and Oil Analyzers Inc are reputable companies that do fluid analysis. Analysis usually costs about $25.

Edited July 18, 2013 by Fairtax4me

[MilesFox]

I would guess the coolant was low when you brought it in. The mechanic may have added coolant and whatnot.

 

Either it wasnt burped properly, or the damage was already done from the last overheat, allowing the HG to fai a little, and now it is failing the rest of the way.

 

MAybe your mechanic didnt want to scare you suggesting the HG needs replaced without trying a new cap at least.

[wolfweb]

here's what happened: I took it in for a service, the mechanic said the radiator failed a pressure test so he ordered a new cap. Couple of days later I had the cap fitted, the radiator passed the pressure test. The next day after a 30 min trip the car boiled, temp into red just after I stopped at my gate. I've never had trouble with overheating beofre he replaced the cap.

 

Took it back worried it was a head gasket or cracked head. They did a block test on it, it passed.

 

he found a small leak in a hose but doesnt think that caused the overheating.

 

Now he's checking the thermostat and said he'll take it for a drive today to see how it performs.

[Fairtax4me]

Just doesn't make sense to me. To pressure test the radiator you have to remove the cap, the cap is not on the radiator while doing a pressure test.

There are adapters that can test the cap by itself, but the system can't be pressure tested while the cap is on.

 

Maybe the cap failed the pressure test. But a new cap should not have caused it to overheat unless its a cheap aftermarket part, or the wrong pressure rating. 13 psi is what most Subarus use. But there are caps that will fit that are as low as 7 psi. Low pressure in the cooling system can allow the coolant to boil which will lead to overheating.

 

Subarus are very picky about thermostats. An aftermarket thermostat of the wrong design will just cause more overheating. There are only a few that are of the same design as the OEM and will function the correct way.

 

The problem your having is more likely due to low coolant level, than a bad thermostat.

[MilesFox]

Have your mechanic add coolant to the block via the upper radiator hose if he is confident there are no loeaks. It is tricky to get the aur pocket out of these engines.

[wolfweb]

He's found it was the new radiator cap. It was an aftermarket one, not subaru genuine part. The are two metal lugs that hold it on tight. One of these lugs was smaller than the other. This meant under pressure one side of the cap popped off. It wasnt off enough to notice, just enough to lose pressure which resulted in the overheating. A new cap was fitted and no overheating, no loss of fluid so far. He seems to think the loss of fluid was it being forced out of the radiator into the reserve tank.

 

I again asked him why it had never overheated using the original cap which he said failed a pressure test and he said it probably held enough pressure? But it was losing fluid with the original cap, so something seems to have been wrong with it, again he says it was probably forced into the reserve.

 

Still monitoring the fluid to make sure there is no more loss.

 

Thanks for your help everyone, amazing how you all got it so right not seeing the car and relying on my noob relaying of the facts.

 

I fot it wrong about the pressure test. The radiator never failed that. The original cap failed the test. He did not test the new cap which i guess is normal but that would have saved him lots of trouble and my subie overheating.. I hope there is no damage, he said no because it passed the block test and there is little else that could be wrong due to the overheating, according to him.