No one I know can figure this out. 350ci, stock water pump and radiator, new 180 thermostat. Cheap temp gauge from autozone. After I drive my car for 3-5 minutes, the temp will jump from around 170 to 190 to 210 to 230 to 245. and it jumps, it dosent steadily rise. So while its doin that I rev it up to 4500rpm and the temp immedietly drops back to 180ish. It will stay there for a second, then do it again. It does this 3-4 times, then it stops and everything is normal. I thougth it was sucking in air cuz my water pump wasnt completely sealed against the block, but i fixed that and it still does this crazy thing. Should I get a new thermostat, or is mabey my gauge just faulty? How can an engine temp just jump like that?

 

try a new t-stat, a 180* with somw 1/8" holes in it would be ideal

 

Is it possible that you have air pockets in the coolant systeM??? U could try starting the car cold with the rad cap off and let it warm up. If you have air in the system it should come bubling out without the cap holding pressure and youll notice the coolant level droping in your rad. If you havent gotten the air out there could still be some trapped from the previous leak.

 

I'll give you some things to look for! In no way am I critisizing you mech. ability, but we all make mistakes and sometimes overlook the obvious.

1. Thermostat installed incorrectly
2. Water pump vanes worn or corroded
3. Mechanical fan installed backwards
4. radiator core pluged up
5. Bottom radiator hose spring rusted and hose colapsing

It sounds like you have a flow problem otherwise it wouldn't cool down when you rev it up.
A good way to diagnos a flow problem is remove the radiator cap, make sure the coolant level is up and put a towel in front of the radiator so the engine will get good and warm. Once it does the thermostat should open, then you can observe the flow of coolant through the radiator end tank. Even at idle, you should have good flow through it. If you don't, I would suspect a worn out water pump, or a radiator that is corroded through the core.
If you do have good flow, check the temp. with an automotive therm. and see if the thermostat is opening at the correct temp.
If not replace the stat! If your core is pluged, a new one is only about 100 bucks from modine. Good luck!

 

Put a new stat in. It still does it!

 

I ran the engine with the rad cap off and let the water pour out. When it got to 220* alot of steam came out and the water splashed out in drops, it didnt pour out anymore. Shut it off, refilled it and it still does the temp jump. Mabey I am sucking in air from somewhere else?

 

read the sticky at the top of the cooling page from Breathment. There is plenty of info there. There are links in blue about overheating etc. Its just a process of elimination basically. There can only be so many things causing your problem. It could be the timing is off, bad rad cap, clogged rad, bad thermostat (even tho its new) etc. etc. Hope this helps.

 

Everything talks about overheating in general, my car dosent realy overheat, the temp just fluctuates rapidly, and the faster the engine is the cooler the temp is, the opposet of most overheating.

 

it still gives you ideas... you could just have a bad gauge. Get a heat gun and check the intake temp as compared to the gauge reading.

 

I'd start there.