Cooling fans run after engine shut down.

MIKE VARNUM

MEMBER
HONDA PRELUDE

I have a 95 Honda Prelude, 151K miles with a four cylinder engine. After running at normal speeds and stopping at intersections the temp gauage starts to rise. Once moving again, air flow cools the engine and temp gauge goes back normal. Upon stopping the engine and after maybe 30 seconds the cooling fans come on and blow for most of five minutes. Shouldn't the fan come on to prevent the temp gauage from raising? Where would I find the sensors that control the fans operation? I had a shop check the problem and they said everything checked OK, but when your sitting at a red light and the temp gauage starts clicking towards HOT! Something ain't right. Coolant is topped and fresh. Radiator and hoses replaced about a year ago. Changed thermostat and radiator cap to see if that would help. Didn't happen. Whatcha think?

4 Replies

BRUCE HUNT

MECHANIC
3,753 POSTS

You say the coolant is topped off. Honest, answer to the question, does the vehicle use any coolant? Unless the radiator is blocked in someway that would be the only explanation. What is the condition of the radiator?

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Tuesday, January 30th, 2007 AT 10:32 AM

MIKE VARNUM

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I have to add some coolant to the over-flow tank every now and then, but coolant is alway full in the radiator. I had the radiator and hoses replaced about a year ago. On many of your cooling problem questions, I see where you suggest that air is purged out of the system. I'll give that a try and then I'll move on to the sensors. Both fans work, one fan runs when I turn on the A/C and the other, which I feel should run to cool the engine, only comes on when I shut the engine down. I'm hoping it's an air problem and the sensors are getting false readings. Wishing for a simply fix. Appreciate your help in resolving my problem, Thanks.

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Tuesday, January 30th, 2007 AT 7:25 PM

BRUCE HUNT

MECHANIC
3,753 POSTS

Air in the system could cause this but generally the air will cause the engine to surge. The one fan should run when the A/C is on. It cools A/C lines. The other will run when the temp sensor tells it to run. I think in this case it is trying to tell you that the engine is too hot. I seriously think you have an underlying problem. You will need to face it eventually. The coolant is going somewhere. The car wants more water to cool it. So here is what I think. Check the radiator closely for a leak. Any area of wetness. The two big possibilities for the low level of coolant are slow burning of coolant in engine by a head gasket leak or a plugged radiator that restricts the flow of coolant through the lines. The engine gets hot because of two things - not enough coolant present and restrict ability to cool.

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Tuesday, January 30th, 2007 AT 10:16 PM

MIKE VARNUM

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I really appreciate your help with this issue. I drove my Prelude to bring up engine temp. Checked for leaks as you suggested and observed fan operations. With the engine showing normal temp, I shut it down and within 30 seconds or so the cooling fan came on. I turned the key to the on position, without starting the engine and the fan went off. So, I started the engine and the fan remained off. I then turned on the A/C and it's fan started, turned the A/C off and it's fan stopped. While the hood was up, engine running I again checked for leaks, none to be found and the over-flow tank had coolant up to the full mark. I proceeded to bled air from the system, had to use a socket to crack the bledder, using an open end was not gonna work, cause that hammer-knocker was HOT! Anyway, upon cracking the bledder, I couldn't tell if air escaped, but I did see coolant, plus to my surprise the cooling fan came on. I checked the temp guage and it read normal. Not sure if this was just a fluke, I restarted the engine and let'r run and sure enough after a while the cooling fan fired up and the temp guage still read normal. I'll give'r the highway test and let you know the results. Thanks and we'll talk with you later.

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Friday, February 2nd, 2007 AT 7:07 AM