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Old 05-12-2011, 11:20 PM   #1
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Default Overheat when under boost

When i run on the freeway around 75mph on a 60-70 degree day it begins to heat up rapidly, but under 70 is all right and cools it right back off. any ideas?
Ps on a 75-80+ degree day its around 65mph.
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Old 05-12-2011, 11:29 PM   #2
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blown headgasket
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Old 05-12-2011, 11:38 PM   #3
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I had the same problem, only when the AC was on. Turned out the relay was bad and the AC fan wasn't working. I'd check the fans to make sure they come on. You also want to make sure you have the undertray on, that's is pretty much going to eliminate the pressure differential across the radiator at speed which would cause it to overheat.
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Old 05-12-2011, 11:43 PM   #4
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Do you have any ducting? If not get some, and a bigger rad.
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Old 05-12-2011, 11:44 PM   #5
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Even sealing up the factory air guide and under engine panel to force air through thr radiator helps out dramatically.
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Old 05-13-2011, 12:13 AM   #6
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My stock radiator handles cooling just fine, you really shouldn't need to upgrade on a streetcar. The answer is most likely:

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Old 05-13-2011, 01:21 AM   #7
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Quote:
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My stock radiator handles cooling just fine, you really shouldn't need to upgrade on a streetcar. The answer is most likely:

2nd this
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Old 05-13-2011, 01:38 AM   #8
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I drove mine through 2 Virginia summers beating the living crap out of it daily and didn't have the understray installed. My only coolant mod was an all-metal auto-radiator. I also did not have A/C. Some cars have instant problems when the undertray is removed, some cars see no difference.
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Old 05-13-2011, 07:09 AM   #9
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blown headgasket
the head gaskets fine, theres no coolant in the oil.
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Old 05-13-2011, 07:11 AM   #10
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Quote:
Originally Posted by pdexta View Post
My stock radiator handles cooling just fine, you really shouldn't need to upgrade on a streetcar. The answer is most likely:

my car does not have that. the intercooler was positioned wrong and they must have thrown it away. idk i wasnt the one doing the turbo upgrade.
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Old 05-13-2011, 07:13 AM   #11
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Quote:
Originally Posted by pdexta View Post
I had the same problem, only when the AC was on. Turned out the relay was bad and the AC fan wasn't working. I'd check the fans to make sure they come on. You also want to make sure you have the undertray on, that's is pretty much going to eliminate the pressure differential across the radiator at speed which would cause it to overheat.
my car has ac, but it dosnt work, and someone removed the second cooling fan to put a bov on.
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Old 05-13-2011, 09:27 AM   #12
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Quote:
Originally Posted by redturbomiata View Post
the head gaskets fine, theres no coolant in the oil.
that doesnt have to happen to have a blown head gasket. coolant could be leaking directly into the combustion chamber, without any loss of oil.

exploding gas and oxygen is pretty damn hot.


but your issue doesn't sound like this is the case, it would also idle like crap.

whats your cooling system like? stock? undertray removed? intercooler? whens the last time you checked your coolant levels?
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Old 05-13-2011, 09:44 AM   #13
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Just having the under tray doesn't always do it. My car has a 3" thick ic as big as the "mouth" with ac behind that then a thick rad, while the under tray helps so does a reroute and the most helpful was the larger rad so far. I think the biggest help for me will be "mouth ducting" as mine is poor / non existent and the airflow goes out the wheel wells. My iat deltas are 1-2C so there must be some flow.

You'll need both fans wired together. I am fine temp wise until I go over 110-115kph, over 120kph (~75mph) my heat sits at 102C from the normal 93-97C.
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Old 05-13-2011, 09:47 AM   #14
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Try changing your thermostat first. They do fail on occasion.
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Old 05-13-2011, 09:51 AM   #15
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you shouldnt need fans at all just driving around. fans should only be coming on when you're stopped.

I have a smaller all aluminum radiator, and it's uncommon for the fan (singular) to come on. I average 185-187F coolant temps. If I sit in traffic they can come up to 200F where my stock fan comes on and the temps quickly drop back to 190F where the fan shuts off and the cycle continues. If I start to drive again, temps drop back down to 185-187F. If I do boosted pulls (fan disabled over 75% TPS) the temps will increase, but it's nothing that the fan and overall MPHs can't handle.

If you need dual fans in this situation, it seems to me that your cooling system is not up to snuff.
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Old 05-13-2011, 11:09 AM   #16
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get high pressure water hose with 1/4" ID

get schrader valve to 1/4" barb fitting

stick hose on fitting and other end on overflow nipple

remove radiator cap and place something in the hole that allows the LARGE OD seal to seat and the smaller one NOT to seat. A bent paperclip will work.

replace radiator cap

pump up cooling system with bike pump. it should hold 20 psi almost indefinitely.
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Old 05-21-2011, 05:21 AM   #17
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Is your ignition timing correct? When your timing is too much retarded you waste energy in the exhaust, driving up temperatures fast.
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Old 05-21-2011, 08:25 AM   #18
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There is no way the fans should be on when driving. Fans move less air than driving at 30. Ive been testing cooling( see the humongous duct thread in race prep) and lately ive been running no fans at all. With only ducting installed. And only in front of the radiator with no vents in bonnet, running a stock radiator, i overheAt under jogging pace and i can redline it through the gears and when it gets to 100mph its cool again. Retarded timing increases exhaust temp not engine temp.
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Old 05-21-2011, 09:59 AM   #19
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Quote:
Originally Posted by redturbomiata View Post
my car has ac, but it dosnt work, and someone removed the second cooling fan to put a bov on.
If you're not going to fix the AC go ahead and pull the condenser out, that should help airflow a good bit.
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Old 05-21-2011, 01:58 PM   #20
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Quote:
Originally Posted by nitrodann View Post
There is no way the fans should be on when driving. Fans move less air than driving at 30. Ive been testing cooling( see the humongous duct thread in race prep) and lately ive been running no fans at all. With only ducting installed. And only in front of the radiator with no vents in bonnet, running a stock radiator, i overheAt under jogging pace and i can redline it through the gears and when it gets to 100mph its cool again. Retarded timing increases exhaust temp not engine temp.
I disagree, I have seen this personally. When I had a saab 900 turbo, a rock shattered my nice used starion FMIC. While I was waiting on a newer IC, I used a crossover pipe. This car was so hightech that I had a vacuum advance distributor on it. So I retarded my timing. Too much. I didn't bother to to line it up. Ends up, I had it retarded a few degrees too much. It kept overheating as soon as I did this. I would pull the car over wait... start driving again. This went on and I replaced my thermostat. Then I talked to a mechanic buddy, Told him what I did. He laughed and we set my timing correctly, and no over heating.
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