Overheating and Boiling Coolent

Hi guys, I was driving home last night and noticed my check engine light on. When I pulled over steam was coming out of the front driver side of my protege 5. When I opened the hood the coolent was boiling and steaming in the coolent resovoir. I let my car cool for a bit, refilled the coollent and drove around the block. Immediately within half a block the temperature shot up. I pulled over and took a look and did not see any noticable leaking. The weird thing is that if the car runs at idle the temps are fine. When I drive and put it under load it heats up. So today I go back to my car, check the coolent level and its way down in the resovoir so I figure it sucking it back into the radiator. I fill it up, start the car, and at idle the temps are normal. I start to drive up the block and it looked okay other than a slight uptick on the guage. I then figure I can drive it home, so I end up turning on the heater at full blast and jumping on the freeway. On my drive home the temp shoot up depending on how much throttle I apply. Since I have a manual I coast to cool it down. This works for approx 10-15 miles. Then I get to my hometown and notice it rising again at an alarming rate. I check under the hood and the resovoir is boiling again. I've checked the radiator cap visually, upper/lower radiator hose, fan movement, areas around the resovioir and don't see anything strange. I did see fluid dripping from my car but I think that's from the boiling overflow that spewed all over. Any ideas what the problem could be? My next guess is thermostat or a clogged radiator. Sorry for the long read, Thanks for the help!

Weird. If your thermostat had frozen shut, you'd overheat at idle, too.
Sure your readiator cap is on properly and working? If that's knackered, the coolant will boil a lot easier as the system won't be pressurized.

I'd try replacing the themostat anyway, and if that doesn't do it, replace the rad cap - they are both fairly cheap.

If you're worried about a blockage, you could try flushing the system with a hose, then running some "radflush" solution through there.

falsedawn said:

Weird. If your thermostat had frozen shut, you'd overheat at idle, too.
Sure your readiator cap is on properly and working? If that's knackered, the coolant will boil a lot easier as the system won't be pressurized.

I'd try replacing the themostat anyway, and if that doesn't do it, replace the rad cap - they are both fairly cheap.

If you're worried about a blockage, you could try flushing the system with a hose, then running some "radflush" solution through there.

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Thanks FalseDawn that was a quick reply! I am going to try that this afternoon. Any ideas if you should see coolent movement up near the area underneath the cap? Seems pretty still. Thanks guys for your advice!

As far as I know, you should see movement when the thermostat is open only. With the car at idle, I doubt if you'll see much coolant movement unless you have someone hold it at a fast idle (2K say).
You could try disconnecting the electic fan so there's more chance of the thermostat opening when idling, but keep a very close eye on your temp gauge if you do!

Personally, I wouldn't risk running an engine that's overheating at all until the issue is resolved.

Thanks. I will try to the test for the thermostat. I hope it's not the waterpump or something major like that. I did hear that they recommend the waterpump to be replaced after a timing belt change cause it's all in the same area. How often do those go bad? Could it be the waterpump is not pushing enough water through the engine? Thanks!

How often do those go bad?

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They should really last the life of the engine, but I guess like anything mechanical, can break sporadically.
If the water pump is indeed "broken", then yes, you will get serious overheating. Did you see water moving with the rad cap off and the engine at normal temps?

Let us know how you get on!

Duuuuuddde. These are the exact same symptoms of my Mustang with a bad head.

Have a garage do an exhaust gas 'sniffer' check at the radiator cap. Any exhaust gas indicates a crack in the head.

Thanks guys for the advice. I got a new thermostat today. Will try to replace it. Hopefully the cracked head is not the case. This sucks!

sometimes you can see the 'bubbling ' with the rad cap off. Be careful.

P-Funk! said:

sometimes you can see the 'bubbling ' with the rad cap off. Be careful.

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Hey Guys! Thanks for all of the help! I replaced the thermostat and my baby is running again! I love this car! I've been driving my mom's accord and I have forgot how my protege drives! Thanks again!