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Overheat issue with a 1998 neon SOHC auto.

Posted: Sat Jul 07, 2012 7:59 pm
by dani9678
I've been working on a friend's 1998 Neon that originally had a blown head gasket that I replaced. I checked to see if the head was warped and it was within specs. I used a multi-layered gasket and new head bolts to install. I replaced the thermostat, both upper and lower hoses and just replaced the radiator yesterday which seemed to have prolonged the time needed for it to overheat. I used a cleaner to run through the coolant system with water to remove the oil that coated the inside of the block and radiator a week before changing the radiator. I was told that the previous owner replaced the water pump less than a year ago. I have noticed that the cooling fans seem to be erratic. After the engine reaches 201 degrees, the fans would come on and stay until it got down to 190. Then they wouldn't cycle back on again until I turned the switch to A/C. By then the temp was up to around 220. They stayed on until it got down to 201 and not cycle back on until it reached 212. I don't know why they came on the first time but not cycle on again until the A/C switch was on. From that point on, it cycled on at 212 and off at 201. I drove the car around and maintained 50 mph in which the temp stayed at 198. When I would come to a light, the hottest it got to was 204 after idling for 2 minutes, it then went back down to 198. This was all done last night. I believe the outside temp was at 87 degrees. Today the car ran fine until this afternoon around 1pm. The outside temp was 94 I think. I got a phone call stating the car was running hot again. I don't know what to do at this point. I've just about run out of ideas. The thermostat is set to open at180 degrees.

Matt

Posted: Sat Jul 07, 2012 8:45 pm
by srt4eh
Bad temp sensor?

Posted: Sat Jul 07, 2012 9:41 pm
by dani9678
Do the cooling fans share the temp sensor with the ECU or do they have their own sensor?

Posted: Sun Jul 08, 2012 2:36 pm
by dani9678
How do I bypass the fan relay so that the fans come on as soon as the key is turned? I want to see if the temps stay down as long as the fans are running.

Thanks
Matt

Posted: Mon Jul 09, 2012 8:00 am
by srt4eh
The ECU triggers the fans to come on so they technically share the sensor. You can get one of those relay jumper wires...I don't know which spots on the relay you plug into though

Posted: Wed Jul 11, 2012 12:15 am
by dani9678
What is the normal operating temp of the coolant for these cars? I was averaging 212 at 40mph with an outside temp of 96 degrees.

Posted: Wed Jul 11, 2012 12:23 pm
by 1genRTturbo
195-210 is about average. my 2.4 swap runs a bit cooler right now, also cause im running redline water wetter and have a 180 thermo. but the 2.0 with cams i ran was average low 200's. you cant really bypass the fan relay. its hooked to constant power. i odnt think anyways.

Posted: Wed Jul 11, 2012 1:32 pm
by dani9678
Do you know if the power feed to the relay is hot at all times? I know with other cars the ECU uses the ground wire to the various sensors and relays as a way of turning them on and off instead of a power feed. Do you know if this is the case with the Neons? I was going to say that if the power feed to the relay is switched on and off by the ECU instead of the ground then what I would do is run a jumper from a switched power source at the engine fuse panel to the relay and tied in to the power feed that is fed from the ECU and use a diode so that the power wouldn't back feed to the ECU and the ECU in turn wouldn't throw a CEL because I removed it from the relay. Otherwise if it uses a switched ground then it's going to be a little more difficult to find another switched ground to pull from because I think only the ECU would have switched grounds. That is if this ECU uses that same principle.

Let me know
Thanks,
Matt