Can someone solve my cooling system riddle?

[Chaotic_Warlord]

Ok I just replaced my water pump and fan clutch on my 95 240, did it all like I was supposed to even gave the waterpump gasket sealer a full 36 hours to cure before I started the car up, wanted to make sure it wouldn't leak. So I let the engine warm up then went for a drive about 3 miles later I was really really overheating, so I turned around and shut off the car for five minutes or so, checked my fluids and topped off the radiator, let it idle for about 30 mins and putting it under load a couple of times by revving and holding it at aroundd 2500 rpms for a minute or 2 and it stayed at the normal operating temperature. So I figured it was fine, left to go again and by the time I reached the same 3 mile point I was already overheating at maximum, or so my gauge said (arrow pointing straight up) since i was already late for work i figured I'd limp it along and see what it would do, by the time I got a couple miles down the road it was starting to cool off, and by the time I got to work about 10 miles from home it was back holding steady at normal operating temp. Now it's doing this, it over heats (just reaches just under the H mark ) stays that way about 2 miles and then rapidly drops back and holds the normal mark. Now I plan to replace the thermostat and see if that helps but could there be somethign wrong with my gauge? I mean it says its overheating but when I turn the heat on all it does is blows cold air and then when the gauge goes back to normal I get nice warm air (which right now in Philly is a good thing) . I understand the risk of running an overheating car and know Im risking my head gasket and damage internally, but I really don't know that the car is overheating. Could I have somehow bumped the temp sensor and made it off or is there air somewhere in my cooling system. Also when I squeeze the top hose at normal operating temp its not hot and there is no surging feel to it. but the car runs fine, no noticeable knock or fuel consumption I don't have any new oil leaks. I'm so confused, but like I said I plan to replace the thermostat, and I take it in wed to have the EGR solenoid replaced so I was planning on having them do a full cooling system check and flush while they're at it. Any help would be much appreciated.

[pr240sx]

I am sure that your thermostat is working just fine.You have a air in your system!!To purge, try this:Raise the front of the car as high as you can (or use a steep incline)car cool, engine cool (not warm or slightly warm, COOL!!) remove the air bleeder screw, near the top radiator hose connector in the engine (10 mm bolt and DO NOT loose the washer!!)Open the radiator cap, check level, add if necessary. Keep adding until you see coolant bleeding from the air relief plug. Install screw (helps if you install the screw with coolant bleeding out the hole)move the AC temp to heat (full blast) no need to turn on the fan.Start engine and check coolant level. keep adding SLOWLY until completly full. If the car all of the sudden burps air (like a cofee machine) shut down the car, and wait until it cools down again.It helps if you squeeze the top rad hose from time to time to help the air to get out.

Hope this helps!!

[Touchdown038]

I would say thermostat since the top rad. hose is not hot... but it could be air too. Do what pr240sx said and make sure there's no air in it, and if it still does it then the thermostat needs replacement.

[LasVegas240sx]

I had the same f*ing problem. It turned out to be air in the system, I filled the motor up first via the top radiator hose connecting to the block. Filled it until it spilled out. Attached it all out, ran it with the radiator top off for a few minutes.

It did it to me like 3 times, but what my problem was is that my WHOLE system was failed. The previous owner (I have owned the car two months now) had JB Welded the thermostat housing because somehow he broke chunks off of the lip. It was rediculous. He JB Welded the thermostat to the block. Whatever he could have done wrong he did.

Long story short, my entire coolant system is brand new, down to the fan blade (that was what we call a "my bad "

I'd say you can find out the problem yourself, don't even waste your money on the shop. It is a frustrating subject for me to this day

[frapjap]

pr240sx has it exactly right. Follow his instructions. They're damn near what I was going to post.

The only difference is when I fill and have the bleeder screw off, I let the car run until nothing but coolant comes out of the bleed hole, then I cap it.

[Chaotic_Warlord]

Ok problem is fixed, just had the mechanic totally fluch my cooling system while it was in the shop getting the EGR solenoid replaced...just need to get that new valve cover gasket on change the plugs and wires and install the upgraded brakes I have and Ill be good to go , until it gets warm everything else is oon hold.

[ddgsxr504]

To anyone else that reads this thread let it be known that another common cause of overheating is caused by a faulty radiator cap. So before you start replacing the water pump/thermostat ect.... Check this first.

[streetracer]

Don't forget to check your belts to see if they are loose. If the one is loose that goes around the water pump that could couse a over heating problem due to the fact your pump won't move much if the belt is slipping.