Difference in water temp(pfc vs stock gauge)
 

My pfc is acting really weird. I get readings of 88 87c when idling and when driving the temp will stay around normal but a few times when i speed up the pfc temp will drop like 20c to like 77c to 67c and then back to 88c when i slow down. I was driving on the highway and my pfc said 77c to 88c but my stock gauge went up past the middle towards the H and then back to normal. This gauge usually stays 1/4 the way. My water level is still full and i never lose any after shutdown. Is maybe the sensor for the pfc going bad? I have my fans set to come on at 89c.

That's odd. The PFC uses the green ECU water temp sensor for the display, which is typically fairly sturdy and long-lasting.

I have seen cars with colder thermostats get *too* cold on freeway driving with all the extra airflow through the nose of the car, so that is a possiblity.

Might need to go into the PFC's sensor check and see what the sensor is putting out. But, I would have a tendency to believe the PFC more than I would the stock gauge.

Dale

Im pretty sure the stock gauge gets its reading from the spade connector to the right of the oil pressure sending unit

I believe the pfc gives a reading from the water thermosensor which is the top green plug behind the waterpump housing. The plug under that is the fan thermoswitch.

So it sounds like you are having a problem with both of those sensors? maybe theres a bad connection

The PFC gauge is connected to the green connector and senses coolant temps coming out of the block.

The stock gauge is connected to a sensor that senses the temperature of the block, not the coolant.

I saw something similar to what you're seeing: the PFC temperature is stable yet the stock gauge moved up to H. A few weeks later, coolant o-ring seals failure.

Guys the Water Thermoswitch in the filler neck is a 108 deg C on/off switch for coolant fan relay No 3. Above it is the PCM water temp sensor..this is what the PFC reads. The water temp sensor in the side of the block also reads water temp in the blocks water jacket and feeds to the stock gauge.

If readings are true, suggests the t-stat doesn't close properly, and rad cap is leaking internally and losing pressure .... boiling at combustion chambers and spiking stock gauge.


pomanferrari: "The PFC gauge is connected to the green connector and senses coolant temps coming out of the block"

I've never had wp housing off, so not sure if 2 sensors there sense the block exit flow, or wp discharge. know for sure it's block exit?

I have had the WP housing (the one w/o the impeller) off and that is what it looks like, water coming out of the block up to boss portion for the sensors than into the water pump.

Well i hope it is not anything with the coolant o ring seals, This engine was just rebuilt by pineapple and has upgraded coolant seals. I put in a new thermostat when i put the engine back in the car. Its a 180 degree one. It just started to do this after i changed the coolant again and put in some water wetter. The stock gauge only moves when i am going up a hill. Just driving around and at idle it's fine. So could i buy a new cap as long as its the same psi right?