[Mrama004]

Noticed on the last 2 drives (40-50 degrees F ambient) that the car is struggling to get up to engine temp. I don’t think I ever saw it hit 190 or hear fan kick in.

suspecting tstat failed. With the car cold, I started it up and kept my hand the top radiator hose. It gradually warmed up along with the engine; I didn’t feel a sudden rush of heat. The aluminum radiator inlet was red hot too. After the hose was clearly hot I checked the temp gauge and it was hanging out in it’s new favorite spot right in the middle between 100 and 190.

while this feels like the telltale signs of a tstat stuck open, the service manual instructs to use the DRB scan tool if the temp guage is low.

question is, is an open tstat on a 2001 something that would really create a code? (Is this a dumb question given that the flipping SM implies it will? Yes, but whatever)

I’d like to confirm as much as possible its a failed tstat before I jump back into yet another spring season taking off the manifold and thermostat housing. So, if there is more confirmation to chase via diagnostic tool, that’d be good to know.

thanks dudes.

 

[GTS Dean]

With the engine idling in an open garage, it should get the T-stat opened and have the fan cycling. Pretty easy test to run without the DRB. If there is air trapped in the system, the thermostat will not work reliably.

 

[RobV]

on other cars t-stats fail in he closed position. They make fail safe t-stats that remain in the open positions. but as dean pointed out. also on a cold engine you will see when the t-stat opens for the first time.

 

[Mrama004]

With the engine idling in an open garage, it should get the T-stat opened and have the fan cycling. Pretty easy test to run without the DRB. If there is air trapped in the system, the thermostat will not work reliably.

aint doing that like it used to. I’m pretty confident tstat failed in open position, but for giggles I got an OBD scanner and will check for codes and check engine coolant temp.

will report back with fun stuff.

 

[85vett]

Based off your test I'm betting stuck stat as well. If you haven't flushed the system in 3 years (assuming stock green fluid), would be a good time to just change the fluid and check things over real good.

 

[GTS Dean]

I was out driving at lunch. I watched it warm up from cold start and there was no discernible change in climb rate until when it opened and the fan started cycling. Mine cycles between 190 and ~205F.

 

[Mrama004]

So…interesting stuff. I finally got around using the OBD reader.

1) no codes in the computer. I was expecting P0116 (engine coolant temp performance) or P0125 (engine coolant temp not reached).

2) I turned on the engine monitored coolant temp in real time on the OBD. After a few minutes idling, the fan kicked in when the temperature reached 98c/208F. Fan cycle brought the temp down to 92c/197F. Cycled that way 2-3 times then I shut down.

SM states stock thermostat starts to open at 195F and fully opens at 219F.

I don’t recall and can’t quickly find what temp the fan kicks on.

The numbers from the OBD reader look somewhat consistent with the SM.

First pic is what the gauge was reading when the OBD read 98c/208f. Second pic is the guage when the OBD reported 92c/197F. Whats the probability that this is a gauge problem vs. a failed tstat?

 

[GTS Dean]

Normally, I would suspect the sending unit to be faulty but your reader confirms the output readings are pretty close to spec. I would definitely investigate the gauge next. I don't know if the sender and gauge have a signal pairing requirement and perhaps someone else installed a non-OEM sensor in the head at some point previously.

 

[Mrama004]

glad to have your second opinions on the saga and REALLY glad it’s not looking like a failed Tstat given the OBD readouts.

Will next be working out guage situation.

 

[RobV]

The temperature sensor/sending unit is one unit but have 3 output pins.
Pin C to pcm thats what you are reading with your OBD
Pin B to gauge.
Pin A to lamp.

No signal pairing just that the sensor does put on a load onto the gauge so load pairing.