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#4: 11-13-2012, 08:22 PM
taylormac1993's Avatar
Title: Senior Member
Location: Northern Colorado
Car: 1998 Subaru Legacy Outback 5MT Swap
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Originally Posted by broknindarkagain View Post
Bleed the coolant AKA "burping"
I did that when I put the coolant in and it ran fine until it got cold. Would the cold weather suddenly cause air bubbles?

Originally Posted by Kennyfvholla View Post
Okay, so here's what I want you to do. As soon as the temp rises up while driving, shift down until the motor is revving ABOVE 3500 (4000 RPM at the MOST) RPM. This will flow enough coolant through an OPEN thermostat to cool an engine with bad head gaskets or a bad thermostat. Any other issues, and it won't cool down. If it doesn't work at first, try a few more times. Keep the heat ON and at full "defrost." drive like this for a while. Does it cool down? And how long does it take? What does it do with the heat and everything completely off?
I drive the car below 3500 for a reason... I'm almost certain the HGs are fine and that it's the thermo (if anything). My tranny (4EAT) is going bad so I don't want to put any more strain on it by downshifting just to test the cooling system.

Nothing that I do with the HVAC or electronics does anything whatsoever. I've tried with my brights, fogs, and stereo all the way up, heater full blast (defrost and non-defrost), and the opposites of both. I thought the heater would help because that's what you do in a car that's heating up: turn on the heater vents. Also, my cabin air circulation is off. I check every time to make sure.

After you start driving like normal, how long does it take to overheat again (while drving) if it cooled.
On a cold start, it will take probably 10-20 minutes of driving time to start over heating. (in this weather, anyway. I didn't have a problem in the warm months.)

Why speeds does the overheating occur?
Yesterday, it did it while I was going 40. Today, it didn't do it while I was going 25 or 75. I'm pretty sure it has more to do with the duration of driving time and the temperature.

Which water pump do you have? The one where the thermostat is mounted vertical or horizontally?
I have a GMB water pump that was replaced with the rebuild. No additive or any kind of gunk could have (or SHOULD have) clogged it or impaired it. I'm not sure if it mounts vertically or horizontally because I replace it on an engine stand. My guess would be horizontally.

How long does it take for it to start overheating when you FIRST drive it for the day?
How long does it take to overheat when you drive it after you've driven once or a few times?

On a cold start, it's usually 10-20 minutes. Sometimes when I get back in the car after going into a store or something it will start to heat up and sometimes it won't.

Have you replaced the thermostat before?
I have replaced it with a Duralast part from AutoZone. It was cheap and I was in a bind. If I replace it again, I'll be sure to use the factory part from a dealer.

One more thing: I've noticed that on long stretches of road with minimal stoplights it tends to heat up faster than in city/stop and go traffic. This has nothing to do with the speed either.