Temperature gauge fluctuating and engine RPM "boucing&q

HROONK

MEMBER
HONDA ACCORD

I have a 1995 Accord that I bought last spring. It has 160,000 miles on it and the temperature gauge is acting a little funky.

After the car has been warmed up, if I run the heater/defroster, the temp gauage will drop down to zero. Once the heater is turned off, the temp will slowly climb back to it's normal position. Also, on two occasions after a highway commute the engine RMP has "bounced" rapidly back and forth between 1800 and 900 RPM once I come to a stop and idle.

I was hoping that I just had a bad sensor or thermostat, but after popping the hood, I was a little low on coolant. This could indicate a bad head gasket, correct?

For the time being, I bought a new temp sensor and themorstat and am hoping for the cheap fix. My question is, there are 3 sensors on left side of the engine, which one is the coolant sensor that goes to the gauge? It looks like the center, lowest one under the distributor cap.

Any guesses as to the correlation between turning the heat on and the temp dropping?

I hope it's not a head gasket as I only paid $2500 for the car and am not going to put in another $1500 to have the head gasket replaced.

Thanks

5 Replies

MIKEYBDMAN

MECHANIC
623 POSTS

Ok, to start with, how fast does the temp drop to zero when you apply heat? I know in cold weather if the thermostat is stuck open, when you run the heat it asks like an additional radiator to cool the fluid. Does the car take a long time to heat up when it is cold?
With the RPM flux, is that an indication issues, or does the actualy engine drop and raise with the RPM indication?
How often are you having to add fluid? I would check my oil and make sure radiator fluid is not getting into the oil, and proabably use a pressure tester to isolate any radiator fluid leaks.

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Wednesday, January 3rd, 2007 AT 2:23 PM

HROONK

MEMBER
2 POSTS

The temp gauge drops very slowly, but steady to zero.

The actual engine revs and lowers with the RPM reading as if you were quickly placing your foot on the gas pedal and taking it off.

I have only added fluid once, but am keeping a steady eye on it now. I am trying to locate a pressure tester to test for radiator leaks.

Thanks

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Wednesday, January 3rd, 2007 AT 2:27 PM

MIKEYBDMAN

MECHANIC
623 POSTS

Ok, I think a new thermostat will fix your heat problem. It should keep your radiator temperature up even with the cooling effect of using your heat.

Sounds like your engine is just cutting out on you while running. Could be loosing spark or fuel. Are you getting any engine codes, or service engine soon light? If so, that will probably lead you to why you are losing fire. If not, then I would test the fuel system and you might want to run the car on a test machine. That would show what is getting dropped when your RPM's drop.
I know the PGM-FI relay is a common problem on these cars. Might look into testing that relay.

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Wednesday, January 3rd, 2007 AT 3:24 PM

BRUCE HUNT

MECHANIC
3,754 POSTS

The bouncing of the engine idle speed I would wager is directly related to this same problem. Fix the coolant issue and bleed the system. You will probably see the removal of air from the system cure the bouncing idle. Air causes some of the sensors to misinterpret the temp of the vehicle and ask for more fuel and then it thinks it got too much and it will fluctuate.

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Wednesday, January 3rd, 2007 AT 5:25 PM

CURTISMARTELL

MEMBER
30 POSTS

Hey. I have a 2003 Honda Civic and have the exact same 2 problems as you. I replaced the temp sensor, with no luck, and got honda to replace the thermostat for me. Still having the same problems though. I doubt it's the head gasket, as I do not know much about cars, but I would tend to think it would make the temp gauge heat up instead of dropping. Any other help on this issue would greatly be appreciated.