jesshaines

Hello y'all

Ive got a 2000 civic with a known head gasket leak. Because it also has a tranny with one toe in the grave and a bunch of cosmetic issues, I was kindof thinking of just running it till it blows chunks and being happy with that. So that plan was going okay until I started travelling to Palm Springs twice a week, which means going up steep grade for several (maybe 5?) miles. And thats when issue pressnted itself.....

the last and only time I came up that hill, temperature guage began climbing quickly, but as soon as I let off the gas, it dipped back down again. I pulled over twice to manually check temp at radiator cap (I dont trust guage 100%) and it wasn't too hot. This happened several times. Its a steep grade with only a few places to pull over, and at the last steep section, I made it over the crest before hitting redline but just barely. Then, guage swung quickly back down to normal and stayed that way.

so I'm thinking of replacing hg - yes, I know it needs to be done, but I am wondering if in the end this is going to solve this problem. As I understand it, blown out hg in of itself wont cause overheating, just the associated loss of coolant. Also, ive never personally seen a car that temp goes up and down so suddenly and quickly.

incidentally its hot as ***** here (sometimes 120f) and oh yeah, cooling fan isnt coming on either. Also know that needs to be resolved, but again, does that explain rapid heating and cooling?

If I get in there to change hg, anything I should look for that might be causing this?

thanks

Jimi Hondrix

Read: Head Gasket Problems - Causes and Solutions Simplified!

Do a Block Test on the engine...free rental at Auto parts stores. Fix the radiator fan issue... try jumping it (youtube).

Automatic or manual transmission and what is the issue with it?

2x0

Sounds like the blown HG is allowing compression to leak air into the coolant, making bubbles which will throw off the temp gauge. So yes, most likely fixing the HG will solve the issue, assuming your rad fan, thermostat, and water pump are all good.

mk378

Don't drive with a bad head gasket. The more you drive with a blown gasket, the less likely a new gasket is going to fix it.

When a bubble of air forms in the engine, coolant can't flow to the radiator. So yeah the radiator may stay relatively cool that doesn't prove anything.

Asphalt Art

The rapid fluctuation is caused by air pockets surrounding the sensor, which is mounted on a higher point of the cooling system.

When the temperature gauge is surrounded by air, it appears to overheat as the air has less heat transfer capabilities in an enclosed system. Everything around it is the same temperature, so it cannot dissipate.

When the cooling system purges the air through the cap (filling your overflow in the process) it allows coolant to again surround or at least splash the sensor, temporarily cooling it back to actual coolant temps.

This cycle is why you see the repeated fluctuation on your gauge.

jesshaines

I had it in the shop a while back and they said they had done a test for head gasket involving a color change. Im assuming they meant block test then?.....but I could do it agajn to be sure.

ive tried jumping fan and it works when jumped but now when I turn on ac.....? Ive replaced switch too. I think the next thing will be to check switch with voltmeter (?) Perhaps it was bad out the box, making sure there good connection between harness and switch etc. Any other ideas?

its auto. Check engine light comes on at about 60mph. Ive cleared code multiple times and thats always the case. Oh, its the torque converter code. Changed tranny oil and it appears solenoid were changed recently but before I purchased. And the shop checked them out and said theynworked. Its runs and shifts fine, smooth. So, im thinkjng pump is going but isnt so bad that it will kick on the cel until high speeds. Who knows how long before its actually goes.... Ive had vehicle form 4 months, 5k and no chnage. But, unlike the dishonest person whomsold it to me, I wouldn't pass it on to somebody else without telling them. I guess it was my fault....only ran it to about 50 mph on test drive.

Asphalt Art

8/10 times, whatever you have to bypass electrically to provoke operation is the problem. The other 2/10 chance is that the switch can be functional, but not be allowed to operate by whatever situation it requires. the wiring can also be damaged at that location and movement while bypassing it, allowing proper contact as well.

If you can bypass the switch alone for the fan to operate, that's the remedy, replace the switch. You can test the switch with a multimeter, just heat the switch to its required temp and do a continuity check across the terminals.

jesshaines

thank you. Very helpful.