First of all I have a 2000 model 2200 ohv engine with a recent auto to manual trans swap. I have been having a bit of a problem. When Im at lower rpms wether doing 70mph or 40 mph if im in a higher gear with low rpms and a steady cruizing speed my car starts to overheat 240-250ish. When I down shift to bring the rpms up the temp automaticly drops quickly to a normal temp. I have replaced the thermostat, the radiator cap, done a flush on the cooling system and because of a bearing failure I replaced the water pump. Also have had the head rebuilt and I put new a new headgasket on (obviously lol) and have done the test for a blown headgasket since and all test passed. This could have been a problem for some time but just never showed up cause of the horrible 3 speed trans that was in it before was at high rpms all the time because of the gearing. Im at a loss and broke. I would like to hear any suggestions you might have. I would also like to know if there is a way to test the radiator for flow and such to see if it might be restricted.

I would eliminate the thermostat and see how it goes.

I would check to see if the cooling fan is working properly.


- Your not-so-local, untrained, uncertified, backyard mechanic. But my @!#$ runs

Well in research the fan will be shut off by the computer after 38 mph per all data. other than that it works just fine. I also thought I had fixed the problem because the upper rad hose was cold on the radiaor side and hot on the engine side. I replaced the hose because it looked original and it was soft. thought maybe it was colapsing internally causing a blockage, but nope she still runs hot. im thinking new radiator still. I have warrantied the thermostat to see if that was the problem but I dont want to eliminate it because it is suposed to have it, and it needs it for correct opperating temp.

it might be that youve eliminated the transmission range sensor while perfoming the auto to manual swap, this sensor is generally an trans fluid temp sensor as well which will send mixed signals to the pcm about what the engine cooling should be.... ive had this problem on a lot of chryslers, im not sure if its relevant to a cavalier..... and if it is that im not entirely sure about what the fix would be

Is the rad new or old? could have blackage?.

Well i just got a radiator from work off another cavalier that has a small crack in the end tank. Im gonna try to put that one in and see if it fixes my problem as a diagnostic peice. If It fixes it I will put a new one in my car, i just dont want to put another hundred dollars in my car to find out its not the problem.

Sounds to me like you have an air pocket in the engine. At a higher RPM, you're throwing what coolant you have across the sensor bringing its readings down. If this is the case, it's running a lot hotter than 240-250ish. Make sure to purge all the air from the system and try it again. If this doesn't fix your problem, remove the t-stat and purge the air from the system and try again.



Some people have brain storms, others light drizzles. And then there are those that have droughts.

Ok so I had a crappy weekend.... I was thinking that I havent changed the fuel filter since I got the car 2 years ago because the lines were rusted then and it was running fine then. Thought maybe there is a restriction in the fuel that is causing me to run lean under a heavy load w/ lower rpms. Well I took out the fuel filter after fighting the rust and it looked like muddy water coming out the pump side and you could barely blow through it...I was like this is it!! well I put the new filter in it and it started then died.... the fuel pump went out because it wasnt use to spinning that fast....sh*t... put another fuel pump in it and it still freaking overheats. the bleeder screw on the heater hose pipe had snapped off but I let it run for about 45 min everytime I had the cooling system open and it would burp and I could pour almost another gallon in it. Well I am wondering if JCZ is right and it still has an air pocket in the system that I just can't get out, so I went to the junkyard yesterday and got another heater hose pipe with a working bleeder screw and try to see if thats the problem. Im so ready for this to be fixed. BTW the radiator didn't fix my problem either.... fml

Ok I think it is fixed...... of all the stuff that I have tried even with the new line with the bleeder screw on it it still had air in the coolant system. My friend has a tool that pulls down a vacuum to like -25 psi on the coolant system and then sucks in new coolant. after this I could not even get my car to overheat when I tried... oh this is so awesome.