Morning. Car is running absolutely flawless. Rock solid and very pleased, but 3x after the car is fully warmed up I noticed during normal cruise the coolant temp drop into the 50s hang out for a few seconds and slowly climb back up into the 80s. Speaking °C. Did a couple pulls on I595 the other day to shake some dust off and it did it again after a pull.
Air pocket? Doubt it. I would think even if the sensor is dry for a few seconds it would be above 50°c. Possible?
Loose connector? Possibly. I do have a new connector I will swap.
Any other ideas what the most common issue is?

N-Flo, Upgraded water pump, new oem thermostat. All the sensors should be new unless the builder didn't swap them when he installed the new motor.

 

Was there another electrical load cycling at the time? I'm assuming possibly a wiring issue in term of movement or a poor ecu earth or another sensor pulling the 5V signal down. Is TPS doing anything funny?

IT is possible for a bit of a shock to happen if the thermostat is going from bypass to open on warmup if the fluid in the radiator is very cold but I wouldn't think it would happen more than once.

 

​​​​​​​No electrical load cycling that I am aware of. I will eventually be installing some id1700s in the secondary so it will be a good time for me to check the change the connector and the ground.​​​​​​​I am not sure if it actually does it more than once per drive. Something I can keep an eye on. It was only noticeable in the pfc not on the factory gauge. The factory gauge has no mods to it though and is still linear. It just stayed solid "warmed up)The ambient temp is still very warm as I am in the Ft. Lauderdale area. The temp stays below 90c, in the high 80s so the thermostat should have fully cycled a couple times. It runs around 87-88c normally. If it is hot out and in boost a lot will run 93-95max.

 

the factory gauge uses a different sender, so that would point to the bad/loose ground or maybe just a bad coolant temp sensor, they do that

 

First off, what are you reading your coolant temp from? Aftermarket gauge, PFC Commander, Haltech....?

What does the coolant temp gauge in the dash do when this happens?

Most likely a sensor or electrical problem. MAYBE with the cold temps we are having it could be when the thermostat opens it's dumping in very cold coolant from the radiator and dropping the temps.

Dale

 

Replace the sensor

 

This is a reading off the pfc. The factory gauge has no abnormal movement.

 

That's the 2-wire sensor in the back of the water pump housing with the green plug that feeds the water temp to the ECU.

Did your new thermostat have a jiggle pin? If not you may want to drill a small (like 1/8") hole at the top of the thermostat to let some coolant flow when the thermostat is closed.

It does almost sound like the radiator is full of cold coolant since I'm sure you are getting lower than normal air temps right now, especially highway driving. Engine coolant warms up, hits thermostat opening temp, opens it up and them gets hit with 40-50 degree coolant that's in the large aftermarket radiator. Temps drop, thermostat closes, temps work their way back up, repeat.

I would expect different behavior if the sensor was bad. Typically they either work or they don't.

One of the guys here blocks off half his radiator with a piece of cardboard in cooler weather. That gets the engine up to temp faster and doesn't over-cool the car.

Dale

 

ive seen a bunch that were broken such that they were intermittent. the funniest one would go both ways, so sometimes the car was dead cause the ecu thought it was 140c and the sometimes it would flood because the ecu thought it was -40c

 

Thx guys. That's the plug that looks a bit crappy. I will replace the sensor and the plug I guess. Cheap insurance. I could block the radiator a bit, but she does get up to temp, just takes awhile. Dale I don't remember if I drilled this thermostat or not. I could check it out.

 

This definitely sounds like a electrical issue, since it is not that realistic to have a 30°C fluid temperature swing in a couple of seconds under normal circumstances. I would check for bad sensor or wiring as mentioned above.

 

I have seen these sensors fail/go bad. If it's original, the sensor is suspect and should be replaced. If that doesn't change the observed behavior at least you know you have a good one.

 

That's exactly what used to happen on my old FC. I can't remember where the water temp. sensor was installed but essentially the car would heat up to the thermostats opening point, and then suddenly the temp. gauge would dip significantly as it opened up and the radiator became in-path. I'd say if this is only happening once after startup (and not intermittently during driving) and at a regular temperature, you can assume that's what is happening.

 

Thx guys I will keep you posted as I go fwd.... when I get a chance to get it back out.