Help random overheating/temp spike!

apexi287

New Member
Jul 24, 2005
401
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Knoxville, TN
I'm going to explain this the best I can, I've never experienced this kind of over heating issue before so I'm at a stand still. About a week or so ago I was on my way to work everything was running perfectly fine nothing was wrong temp was where it was supposed to be, right when I got to work my temp gauge shot up then dropped back down it's about 5 miles from my house. Ever since then it'll do that same thing every once in a while.

I'll explain my situation from today and it's what happens almost everyday. Car starts fine temp goes to where it is supposed to be, I drove from my house to a local mall through city and highway about 15 or so miles away, no overheating problems no temp spike nothing. After I was there for a good 2 hours I get back in my car to head back home, everythings fine but then randomely my temp gauge spikes then drops back down, it gradually keeps spiking up hotter and hotter until it is pegged at the top. I pulled over and the coolant in the over flow is slightly bubbling but not horribly like it normally would when the temp is pegged. I sit there for about 5 mins to let it cool down and it does, drive to my class which is about the same distance and this time there was absolutely no problem no temp spike nothing. It's random but it keeps happening.

This all started before I did a HG job which I finished on friday with an HKS metal HG and arp studs. I have also replaced the rad cap and thermostat. The radiator is also newer I have reciepts from the previous owner. I also have a slimline fan and it is working along with the small stocker(Wired together). I have burped the system and there are also no leaks. Like I said I'm at a standstill and don't really know what to do, the head was also pressure tested when the HG was done.

Also depending on the load of the motor it'll decrease the temp, if I'm in third it'll usually rise a little bit and any other gear it'll drop to normal, also everyonce in a while if I accelerate hard through gears the temp gauge will drop under normal temps but will then go right back to normal after.

:1zhelp:
 

apexi287

New Member
Jul 24, 2005
401
0
0
Knoxville, TN
Yeah I know they arn't accurate I was thinking my sending unit may be bad it just gets to me and scares me a bit seeing it spike like that. I wouldn't even think a stock gauge would do that.
 

mk3ftMFw

Mini Toon Burnout!! FTW!!
Jan 24, 2007
95
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Cincy
the bubbling scares me....

Mine used to spike, i bought a new fluidyne radiator and things have been good since. But i doubt the radiator is your problem... But yeah i would invest in an aftermarket gauge first off.
 

boosted17

Member
Jun 5, 2005
235
0
0
Florence, KY
Mine was just barley overheating when I would get on it. If I was cruising on the highway and the motor was never under load I would not overheat. Once the motor was under load the temp would rise a bit but not over heat.
it ended up being a hairline crack in my metal headgasket that got worse.
I hope this doesn't happen to you.
 

apexi287

New Member
Jul 24, 2005
401
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Knoxville, TN
It'll do it under load more often, but today I have had absolutely no problems I haven't really gotten on it but the temp has been perfect all day. I drove about 15 or so miles straight with not even a slight spike. It would seem too ironic for both the old stock HG and new metal HG to have hairline cracks as this all started with the stock HG on, thus making me do a HG job although I had planned it anyways. I just don't think it's a HG it would boggle me if it was.
 

jdub

Official SM Expert: Motor Oil, Lubricants & Fil
SM Expert
Feb 10, 2006
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Valley of the Sun
Are you using a CT26 with the factory coolant lines installed or are you using an aftermarket oil cooled turbo and blocked the coolant lines off?
 

88YotaTurbo

New Member
Feb 26, 2006
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Wolcott, Ct.
Air in system? Have you tried purging the air?
Run the car with the rad cap off and watch it for bubbling. As the car heats the level will come up a bit but then go down as the T-stat opens. Just watch your temp while doing this.
Also try testing for leaks, but you'll need a specialty tool to do this because you have to pressurize the system.
 

jdub

Official SM Expert: Motor Oil, Lubricants & Fil
SM Expert
Feb 10, 2006
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Valley of the Sun
It sounds like your thermostat is sticking. The reason I asked about the CT26 coolant lines is they act like a bypass to relieve pressure...I blocked mine off and had a similar problem to yours...the blocked lines caused the thermostat to stick closed. The difference is when the thermostat finally opened on my car, the overheat stopped. I removed the jiggle valve on the thermostat and it solved the problem.

What brand of thermostat are you using? Are you sure the e-fans you are using are moving enough air? If you've got a older stock radiator, it might be partially blocked.
 

ImperfectSupra

New Member
May 19, 2007
163
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Virginia Beach
i had a similar problem and it was the upper radiator hose. sometimes it would collapse (flatten out). the first time was i notice was a few weeks ago while under the hood revving the motor. it closed for a few seconds. im not sure what caused it. a blockage or the water pump sucking too hard. i felt the upper rad hose and it was really soft so i did the home depot mod with the 1 1/2 inch sink drain pipe and cut out the old hose for couplings. now i have a hardipe for under $20 and i havent overheat or gauge moved since. though i still have the overflow issue. U SHOULD LOOK INTO THIS!!!!!!!!!!!!!!! im pretty sure at cruising speed the hose would stay flattend for more then a few seconds even more overheating
 
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apexi287

New Member
Jul 24, 2005
401
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0
Knoxville, TN
Thanks for all your guys' input and suggestions, while I was at work today I went over my entire cooling system again. The coolant hose coming out of the heater core was not getting close to hot as I stated before as well as there being no heat. I started messing with the heat turning it up and down to check and see if the heater control valve was working and it was not. So with it not opening all the way I couldn't completely burp the system I had some air bubbles trapped, so I manually opened the valve all the way and re burped the system and got what seemed like most of the air pockets. Took it for a test drive and really got on it, it didn't spike nothing although the temp gauge did slightly raise to about half or a little more but it's no longer over heating.

I'm going to also recirculate the coolant lines from the turbo and see if that will help with the slight raise in temp as well. If you guys have anymore input please feel free to add.
 

ImperfectSupra

New Member
May 19, 2007
163
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Virginia Beach
for me my cooling problems are from lots of little things that add up. leak at thermostat housing, leak hoses, colapse radiator pipe, etc.etc.etc, there are so many things that can cause an overheat so still, pay close attention.
 

apexi287

New Member
Jul 24, 2005
401
0
0
Knoxville, TN
Well it looks like I found my problem it was my heater core it had a slight leak that wasn't noticeable and it kept getting air into the system. It completely went last night all over my foot so I had to bypass it which has cured the spike problem, and it is no longer over heating. Thanks for all the help tho guys.
 

Supracentral

Active Member
Mar 30, 2005
10,542
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36
The MKIII has a FANTASTIC cooling system. If everything is 100% as it should be, that temp needle will never move.

But one little thing wrong, and it's a finicky bastard.

Glad you found it.
 

lppro

LP Performance & off road
Apr 21, 2007
895
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Sugar Hill, Georgia, United States
i have a problam like this. i just put a brand new from toyota t stat and when i drive around the temp will spike then go down a few times.. it vever did this when i was running no t stat so im thinking its a bad t stat? maby its sticking?