Ok, Iv'e search the threads and i'm still at a lost because there were too many different answers.

Anyway I'll start again with my problem.

Today my car started running hot,it went to the third bar when "running" but when I dropped to "idle" it dropped back down.
Usually,from what I read,cars are prone to overheat in the opposite situations.

This is the first timee this has happened so any suggestions would help. I'm gonna run out side right now to bleed the system,BTW both my fans are running so could it be the water pump?

 

Hmmm.....

bump

 

engine blowby... bad head gasket. or bad rings. do a compression test on the cylinders. and might try a pressure check on coolant system.. might be a bad cap or a leak in the coolant system. pressure wise not neccesarily a fluid leak.

 

I'd suspect the t-stat first. If it happened just after you started it, the t-stat was probably a little "lazy" an took a little longer than normal to open up. The water pump tends to be more black and white ... it either works or it's bad ... and not so much "intermittant" ... unless the timing belt is loose.

-Bob P.

 

Have a look at your grounds under the dash and behind the battery in the tray....
TakeCare

 

Billybones.

How would a bad head gasket or rings be causing his over heating pro,blem with out showing other symptoms i.e water in the oil oil in the water? Bad rings would show up in the idel and the drivability of the car not to mention burn through oil like it was gas. Lets not forget the smoke that would be coming out of the tail pipe? Maybe I am wrong on this.. Please elaborate further as I am rinning into a problem very similar to this. I have to dat check the following.

R/R the thermostat rabbit switch
R/R the thermo sending unit to the dash
R/R Radiator and all hoses

Trouble shot the thing down to what I though was the thermostat itself in the water pump and then
R/R the thermostat just to find that the car was still over heating.
My mech tell me that he has seen this before in rebuilt water pumps “That was just replaced in the car a month ago” He is telling me that the water pump is not pushing enough water around the motor. Possibly bad rebuild or poor rebuild quality. He showed me what a properly running water pump should do when bleeding the system of another car. At idle cracking the bleed nut at the top of the motor should produce water seeping from the nut with at least some force. Mine can be completely removed with no water spilling at all. It is not until I rev the motor will water spill from the open hole.

Sorry to rant on but there is not enough water flow from my newly rebuilt water pump thus causing “My over heating problem”. I am curious how the rings or head gasket could cause this type of problem with out showing signs other than over heating the motor.

Thanks
Keith M

 

Well the pump looks ok(coolant comes out of the bleed screw quickly) and my fans are kicking in when they should. So I'll check the grounds but I don't see how that could be it when the fluctuations are so consistent.

Hot under load.

Cool at idle.

Has anyone else have this happen before?

 

Here is an idea as to why you are experiencing this problem. There have been times when the waterpump impellor have seperated from the impellor drive shaft. At idle, there is still enough friction between the impellor and shaft to turn the impellor and circulate coolant; car maintains temp. Under load (driving) the friction is overcome and the impellor no longer spins, coolant no longer circulates and the temps rise.

One way to check for this would be to let the car get up to temp and let idle. Verify that the car is running normal temp then, while stationary, raise the rpm to say 3500-4000 and see if the temp begins to creep up. If this occurs, I'd think you'd have found your problem and need to replace the waterpump.

Let us know what you find.

HTH,

 

Taboo2, blowby of exhaust gasses. It is possible to just blow these by the head gasket, higher pressure at exhaust, upstroke of piston than the 15psi in the water system.. on the downstroke of the piston the intake Valve is wide open the vacccum is at the valve so you do not suck in water. It is easier to move the air in then the water.. Keep in mind that the leak is minute at this point.. exhast gas is very hot. takes only a little to add to the water temp.. Over time though the "worm track" gets larger till it is big enough to let the water in before the air. car runs rough for a few, then all of a sudden it will let go and you get a cylinder of water. Had this exact scenario happen on my toyota.. took a few months did not know it was happening.. at first I could do 55mph no problem.. then 45 then bam it blew thru... took about 6 months.. replaced water pump. belts. and tstat. had radiator recored.... new fan... during the 6 months.. always cool at lower speeds.. Rings being bad heats up the oil slowly and that can cause over heat at higher speeds as the exhaust blows into the crankcase.. My winter beater right now has this problem.. Take off the oil filler cap and you can feel the exhaust blowing out the hole...

 

One last thing taboo2, the compression test and the pressure test did nothing to reveal this problem.. as the car was fine when it was cold I believe. it was sealed.. never saw oil in water or water in oil... until the head gasket "worm track" went all the way thru...The only way to super heat the water is it either is not moving as mentioned above. or it is getting exhaust gasses into the system.. Imho.

 

Did you check the operation and inspect the blades of the radiator fans?