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Why does my car overheat after getting off the freeway

Tiny
KHLOW2008
  • MECHANIC
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Overheating has different and various causes. The correct information and symptoms are vital to rectify the problem. If you start from the basics, I do not see any reason why the problem cannot be solved.

It must be noted that any monitoring of the symptoms and conditions requires some time to be be accurate.

1. Coolant losses only from the recovery tank means there is a leak in the system. It can be anywhere.

2. Coolant losses from radiator but not from recovery tank means a a major leak, a bad radiator cap or head gasket.

3. Overheating at high speed indicates inefficient cooling. It could be the air or coolant flow.
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Friday, August 10th, 2012 AT 4:56 PM
Tiny
ALIK
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Mine started a month after I changed thermostat. Car overheated, did the thermostat test, and that was the problem. About a month later the overheating started. Last night when I read this blog I thought it was me that wrote it. I thought about changing the water pump, but as you sad, water does flow. Not only that, why would reservoir keep felling up? Anyway, i'm thinking, maybe, when it initially overheated something happened in the back of the engine where coolant goes to heater core or its hoses. Thinking about bypassing heater core and see what happens.
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Friday, August 10th, 2012 AT 5:32 PM
Tiny
KICKJON1985
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  • 41 POSTS
What year and make of car do you have? I have a 98 civic and it comes with a bypass stock on it. It does sound like you could have a Pressure leak. How dis the gasket on the thermostat or housing look? Did u replace it?
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Friday, August 10th, 2012 AT 5:44 PM
Tiny
KHLOW2008
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If the reservoir keeps fillig up, there is excessive pressure in system.

It could be any of the following.

1. Bad radiator cap.
2. Bad head gasket.
3. Cooling fan.
4. Stuck thermostat.
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Friday, August 10th, 2012 AT 5:52 PM
Tiny
ALIK
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Kickjon: it's a 2001. Original gasket looked new. Where is your stock bypass?

1. New honda cap.
2. No oil in coolant, nice a green. No coolant in oil, nice and clean. So, hopefully, not gasket.
3. Cooling fans work fine.
4. New honda thermostat.
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Friday, August 10th, 2012 AT 5:58 PM
Tiny
ALIK
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Also, new radiator and hoses. I dissected radiator and there was this black rubbery/plastic substance caked on some parts of it.
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Friday, August 10th, 2012 AT 6:01 PM
Tiny
KHLOW2008
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Honda engine seldoms have oil in coolant or vice versa. A leak down or chemical test would be ideal.
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Friday, August 10th, 2012 AT 6:06 PM
Tiny
ALIK
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Which is more reliable? The coolant reservoir starts to fill up after 20-30 miles and at 3000rpm+. So if it is the gasket, it won't be blowing hot air standing still.
Also, I read that if you torque the head down 10-15 pound more than spec, that should buy you some time, would that work?
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Friday, August 10th, 2012 AT 6:17 PM
Tiny
KICKJON1985
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I agree with khlow2008. If u have black stuff in your radiator, I would block test the coolant system. As for the bypass, the 98 has a valve on the firewall of the engine that when the switch for the heater is moved to hot it opens, but when switched to cold it closes the valve and the coolant is then diverted through a hose back to the engine. This hose, is actually called a bypass hose.
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Friday, August 10th, 2012 AT 6:20 PM
Tiny
KHLOW2008
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Overtorquing can cause the threads to be stripped for this engine and it would depend on the head gasket condition. If problem had been there for quite some time and with steel type gasket, it is not going to help much.

If the overheating occurs under the conditions you mentioned with the fans working continously, I would say the problem is more likely to be cooling efficiency. If the coolant is being sucked back into radiator and with no signs of air trapped in system after engine cools down, that would confirm my suspicions.

However if there are signs of air in system, I would say the head gasket is bad.
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Friday, August 10th, 2012 AT 7:01 PM
Tiny
ALIK
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Would it be the catalytic converter or muffler?
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Saturday, August 11th, 2012 AT 5:12 PM
Tiny
KHLOW2008
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What has the exhaust system got to do with overheating?
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Saturday, August 11th, 2012 AT 6:45 PM
Tiny
KICKJON1985
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Hey KHLow2008,

Recently I have replaced the radiator on my car again, to a oem radiator an replaced all hoses under the hood and the cap. Now I have got pressure in the radiator but, its seams to run over pressure, and it blows all the antifreeze to the overflow. Until it all the coolant is gone the car will run just fine, as soon as it blows all the coolant to the overflow, then it will heat up. It will also not pull the coolant from the overflow to the radiator over night and seems to still have pressure inside the system. I have replaced all parts that can be, does it seem like it just might be a blow head gasket?
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Sunday, August 26th, 2012 AT 9:12 PM
Tiny
KICKJON1985
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Oh and I have conducted 3 block tests on it and the fluid always stays blue. No coolant in the oil, no oil in the coolant, and no white smoke out the exhaust. I have also had someone else start it and smell the exhaust from cold to see if it might be only pulled into the cylinder during a cold engine. But there is no coolant loss, except for what gets boiled over when the overflow fills up all the way.
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Sunday, August 26th, 2012 AT 9:14 PM
Tiny
KHLOW2008
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Too much pressure in system and coolant not being drawn back into system from recovery tank is usually a head gasket problem.

What block test kit did you use? Maybe you should try a different brand to confirm. How much driving time are you able to get before the coolant gets pushed out to the recovery tank? Does the cooling fan run and stop under normal engine operations?

Is the radiator cap good?
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Sunday, August 26th, 2012 AT 9:23 PM
Tiny
KICKJON1985
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The block test is the only tester that is around where I am. Its manufactured by oem. I can get aprox. 30 minutes drive time. This is city driving also, but highway driving I can get only 15 minutes, before the overflow is full and starts to overflow. Yes thefan and everything runs normal alunder normal conditions, it will slowely start to run longer and longer as the radiator runs out of coolant. It stays cool until the system runs low of coolant. The overflow bubbles constantly durring operation in the overflow.
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Sunday, August 26th, 2012 AT 10:37 PM
Tiny
KHLOW2008
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You definitely have a compression leak.
When you remove the head, ensure the head and cylinder face is checked for warping.
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Monday, August 27th, 2012 AT 7:55 AM
Tiny
PARADISEMACE
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Does the reserve tank cap have the down tube on it? If it does, take both radiator hoses off at the engine. Then, with cap on tight, run a garden hose fully flowing into top hose. The water should drop through a new radiator with little or no back pressure. If not, you got a bad radiator off of the shelf.
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Tuesday, June 2nd, 2015 AT 7:14 PM

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