Why does my car overheat after getting off the freeway

The mechanic said the original was loose a bit. But not horribly. I drove it today to see if it would warm up, bu the whole drive it was good till i got home when i went up a little bit then the fan came on and it went down and stayed down. Its just never moved before all this started so its wierd to me.....

When engine cools down. REmove the radiator cap and recheck the coolant level. There is a possibility air is still present system and bleeding is not complete.

Top up if necessary and run engine for a few minutes without the radiator cap and topping as required. You might need to repeat the process a few times.

I will do that. I checked the coolant before i went to work today and found that the overflow was about 3/4 full and the radiator was low. The exact amount that the radiator was low was in the overflow. Boggling that the radiator did not suck the coolant back into the radiator.

This indicates 3 possible scenarios.

1. Bad radiator cap or it is leaking at the neck.
2. Too much air trapped in system.
3. The head gasket has failed.

Well i have changed the thermostat to an OEM thermostat just to make sure that the autozone one i put in wasnt a piece of junk, and still the same thing still. I purchased a block-tester to chem test the system and it should arrive tuesday, so i will conduct this and get back to u to let u know of the findings...

Today i completed the block test and that is negative.... The system is sucking the fluid back into the radiator as normal, but i still have a slight warming problem.... Fans ar working, radiator new, thermostat new and oem, water pump new, have good coolant flow and about a 60-70% anti-freeze mixture. Radiator cap is good and the mechanic shop said pressure test was good. Any other ideas?

Another question.... Is the coolant resevoir suppose to be under any pressure? Even i its not i wonder if it might be bad as when i get out of my car i can smell coolant, but i dont have any leaks, so i assume that the smell is being pushed past the resevoir cap gasket from the pressure and coolant being released into it from the radiator. Any thoughts?

No, recovery tank should not be under any pressure as there is a breather at the cap.

You did not tell me the radiator cap rating when I asked previously.

You mentioned slight warming, how high did the gauge show? Maybe you are paranoid after so much time figuring this out? lol.

The coolant being sucked back indicates the head gaskets should be good.

Oh its a 1.1 cap. The guage sits about 1/3 the way up from the cold, but after a drive in the freeway and the car comes to a stop for a minute (like sitting at a stop light) it will rise to about halfway up. This is odd to me because before i started working on i,t it never moved at all. Maybe it is paranoia.... Any ideas why i can smell coolant so much from outside my car? I had a coworker walk past my car the other day after the car was off for about a half hour and told me he smell antifreeze. And i can smell it pretty good too when exiting the car.

Antifreeze smell stays for a long time when they are spilled inside the engine compartment. Check for any remnants and hose them off.

Do you still need to top up coolant and is the recovery tank level constant or it moves up and down pretty much?

The normal gauge reading should be about 1/2 mark. Does it go down when you start moving?

I havent needed to fill it anymore. As for the coolant level it sits at the full cold when the engine is cold (like sitting all night) and full hot or just above during operation from what i can tell. During the day when it is warmer out, as i live in the utah desert, the coolant all drawn back in the radiator but i assume its because its hot outside an the coolant doesnt cool enough for it to dothis. Yes the gauge will go down to about the 1/3 mark when moving. The fans will eventually bring the temp down from the half mark to the 1/3 mark, at least so far it has, i havent had any real over heating like i did before i changed the waterpump.

The coolant Doesnt all get drawn back into the radiator when its hot out is what i meant to say in my previous post.

There is a possibility the radiator capacity is insufficient for your vehicle.

Do the cooling fans comes on and goes off when the temperature increases? Check the air passagee for radiator for restrictions.

Hmm. It looked the same size as the previous original radiator. The fan does come on and it will bring the temp back down, then it turns off. I worry about it cause of already said paranoia... Lol i will maybe take it to a car wash and spray the radiator off to see if the fins are blocked.

Today while observing it i observed the temp gauge go over half way before the fans started to cool it off. Here is the radiator i purchased:

Spectra CU1290.

I purchased it from a autozone.... This all started when i installed this radiator, maybe it is the reason for my troubles. Any recommendation on a radiator?

I would usually use OEM radiators only. Maybe you can get one from the junkyard.

i have the same problem, i have done everything you have except for water pump. so you all's conclusion is that replacing the water pump should fix the problem/ or fixed yours? and how would water pump go bad? everything i read about water pumps going bad is that they leak. thanks

The impeller of the water pump can wear off or freewheels over the shaft.

I have found that it wasnt the water pump at all. I have replaced 1500 dollars worth of parts and labor and mine is still having the same issue. I would start with a pressure test and a chemical test and see how that goes. When u start the car with the radiator cap off and it gets to operating temp, if u see flow of coolant in the radiator, then its most likely not the pump. Because of the cost to have the pump done i would try and be absolutely sure its that. Everyone told me that it was that, i spent almost a $1000 to get it replaced and mine still has the problem.

Did u do something to cause the problem? I replaced my radiator and thats what started it all.

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.

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.

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?

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.

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.

also, new radiator and hoses. i dissected radiator and there was this black rubbery/plastic substance caked on some parts of it.

Honda engine seldoms have oil in coolant or vice versa. A leak down or chemical test would be ideal.

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?

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.

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.

would it be the catalytic converter or muffler?

What has the exhaust system got to do with overheating?

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?

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....

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?

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.

You definitely have a compression leak.
When you remove the head, ensure the head and cylinder face is checked for warping.

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.