Hello everyone, I've been plagued with engine overheating for the past million years it feels like, and I'm trying to get to the heart of the problem. Things I have done:
- Coolant Flush
- EWP (the summit racing one)
- New WP temp sensor
- Manual fan switch (high only)
- New T-stat (fully opens around 200°)

Everything has helped, but the simple issue is that the water pump sensor reads independently of the sensor in the driver side head.



I thought maybe the sensor in the driver side cylinder head is bad, but when the temp hits ~250° the coolant boils over as it should!

I should note that this only happens after the engine has been idling after a while, or on hot days. Otherwise the temps match up and fans kick in as they should.

My last idea is that maybe I'm just not bleeding the system properly. Any advice would be appreciated. I'm not against drilling & tapping the heads to relocate the WP temp sensor, but it just seems extreme and doesn't solve the problem of WHY the WP sensor is getting stuck.

 

What year and transmission? Not a lot of differences year-to-year, but useful info.

Have you verified the accuracy (resistance vs. temperature) for both the old 2-wire water pump sensor and the replacement? Have you verified the reference voltage from the PCM to the water pump sensor?

Ditto with the 1-wire head sensor - accuracy and reference voltage from gauge circuit?

Test procedure:

4th Gen LT1 F-body Tech Articles

You indicate you added a fan switch. Did you wire it correctly? (this is where year of vehicle makes a difference)

http://shbox.com/1/fan_sw_diagram1.jpg

http://shbox.com/1/fan_sw_diagram2.jpg

And from your description, the fans do not turn on only when idling, except with the switch?

Have you checked the radiator cap pressure?

Drain/Refill procedure:

http://shbox.com/1/4th_gen_tech2.html#radflush

 

My bad, it's the 1995 LT1 with the 4L60-E.

I did the coolant flush and fan switch according to shbox's guides (although I did not force water with a garden hose though the whole thing). I have not done any testing besides the new thermostat, since the 2 wire sensor and radiator cap are basically new. I was also hoping there was a quick obvious fix I was missing. I will test all these hopefully today.

This is the funny part and why I didn't bother testing voltages and resistance before, because everything always works in cold weather! The 1 wire and 2 wire sensor always reasonably match up, and the fan always comes on automatically. I only have problems in the summer after the engine has idled for a while, or coming to a stop after a long drive. The 2 wire sensor gets stuck below the fan-triggering threshold and all the coolant boils out if I don't manually activate the fan.

 

if you have the hoses near the filler nick on the wrong ports, this is what will happen. Check to make sure that your reservoir tank hose is going to the right port.
http://shbox.com/1/95-97_hoses.jpg