Overheating, can't find clear answer.

Well, here it goes. I have a '99 2nd gen 2.5gt auto around 124xxx. New water pump, new temperature sensor, new subaru radiator cap, new autozone thermostat. The car ran fine for a while but recently began overheating pretty regularly and heat it luke warm in the car. It will run at normal operating temperature for around 10 minutes running constantly at highway speeds. After that the heat slowly raises. I did get angry and hit the gas hard once and in high RPMs the heat shot down very quickly. The heat in the car also seems to get much warmer when in high rpms. I originally thought this was a headgasket issue but i'm having second thoughts now. Top hose is hot, radiator is cold all across, and lower hose is cold even after driving. what gets me is, I pulled the hoses off the radiator and flushed it but no obvious blockages. Any ideas?

Start buy putting in a OEM thermostat. Does the temperature go all the way to the top or just runs warm?

it slowly goes all the way up, I have yet to let it go to high but it doesn't seem to stop going up at cruising rpms.

Honestly, if an OE thermostat doesn't fix the issue, you DEFINITELY have a head gasket issue.

BUT, I do not think that replacing the thermostat will fix the issue. When you said you angrily hit the gas and the temp went down, there is a reason to this. I had bad gaskets, when I stepped on the gas and ran the car at 3500 to 4000 RPM the temp came down. This is because you are then running enough coolant at a high enough volumetric rate that it will cool from it's super heated state.

Also, avoid overheating the car too much and like you've been. Too much heat, for too long of a time will cause bearing issues.

Thanks for the input. I don't have coolant in my oil and vice versa. Also, no white smoke. maybe just pressurizing the coolant to the point where the thermostat can't open?

Test coolant for hydrocarbons

did you change the water pump and t-stat because you were having over heating problems?

it could be the t-stat and / or an air pocket in the cooling system.

i'll bet $5 that you did not fill the system properly.
did you remove the vent plug at the top rad hose when you filled it?
did you fill it SLOWLY? this is so important.
did you close the vent plug and run the engine with the rad cap off?
did the system ''burp'' out some coolant and air and then leave room for more coolant?
did you top it off and set the rad cap?

i have a write up of ''siphoning'' the coolant into the rad. it goes so slow you cannot trap an air bubble. do an advanced search for ''siphon coolant'', posted by johnegg . read the oldest first. you get this.

http://legacygt.com/forums/showthrea...siphon+coolant

while you are at it why not replace the cap as well.

When head gaskets go bad, the ignited gases leak through the cylinder seal and into the coolant ports. This super heats the coolant to whereit can't sufficiently cool the motor. That's why it over heats. You won't find any mixing of oil whatsoever. The only way to tell for sure this is happening (besides taking the head apart) is doing a hydrocarbon test as stasis has suggested. You can buy a kit to do this.

And as John has just said, make sure you properly filled the coolant. Are you having any coolant come from the overflow reservoir? If you don't see any coolant in there, you do not have enough in the system and it can't pull more to fill it once the system starts to cool.

I found a new problem that may give a little more clarification to the overall problem. I had the car idling in my driveway for a good half hour with no overheating whatsoever. Around the 30 minute mark, I checked to see if I had any heat from my vents and I had only cold air. Immediately after turning the heat on, The temperature began to rise and wouldn't stop rising even if I turning the heat back off. My gratitude goes out to anyone with some insight into the whole ordeal. If worst comes to worst, I have connections for an eg33 to do a swap.

There is air trapped in the system.
Unscrew the bleed valve on the left side of the radiator & burp the system.
You should be getting heat once its completed its burping process.
If not, it is the thermostat that is at fault.

Originally Posted by DOHCEJ22E1

There is air trapped in the system.
Unscrew the bleed valve on the left side of the radiator & burp the system.
You should be getting heat once its completed its burping process.
If not, it is the thermostat that is at fault.

^This!

Can we please stop referring to "air purging" as burping. Every time someone says it I think of a nasty baby burp.... Blech

But yes, air. Agreed. Purge it from the system!