Engine Running Cold~30° F lower than normal.

[krispy97xlt]

2001 Sport Trac 4x4 Job 2 4.0 SOHC

All,

I recently had my timing chains changed on the front and rear of my engine by a shop. They removed and installed the engine and radiator during the process.

Since getting the car back I have noticed that the gauge runs colder longer and ultimately doesn't get back to the same normal operating temperature as it did before it went to the shop.

Before: Gauge in cluster running at approximately 50%
Temperature read by OBD ~192F +/- 5 deg

Now: Gauge in cluster running at ~30%-40%
Temperature read by OBD ~165 +/- 5 deg

So what could cause this? Did the shop leave out my thermostat?

Did they swap the connectors on my t-stat housing?

Was my cooling fan clutch damaged and now is running only at engine speed?

What things should I check, or is this just due to the change in the weather over the past few weeks?

Thanks for any insight y'all can give.

 

[DjDom]

Yeah, sounds like thermostat is stuck open or missing.
Had the same issue when mine was stuck open.

 

[2000StreetRod]

lower temperature thermostat

If your OBD-II data shows a rapid increase in the ECT after cold engine start and then levels off and stays around 165 degrees then I suspect a lower temperature thermostat was installed.

 

[colintrax]

Does engine temp drop sitting at redlights with the heater blowing? Or while coasting? If so the thermostat is bad. If it's staying at 165 (well close) then they installed a colder thermostat. I have a feeling yours is bad IMHO

 

[krispy97xlt]

I personally replaced the thermostat ~500 miles ago when I was chasing a coolant leak that ended up with me replacing the entire system short of the water pump. The t-stat I purchased was somewhat expensive ($16) but I don't recall the brand or if it was "fail safe"

I stopped by the shop yesterday and spoke with the person that did my timing chain R&R, he didn't remove the thermostat from the housing. They also think the thermostat had gone bad...

I have logged some data from OBD, I will try to graph it and share it with y'all

 

[colintrax]

No need to show us the data lol taking it farther than ya need to. Thermostats are cheap and easy, I say go ahead and replace it again. 99% sure it's bad and you're just wasting gas driving around with a bad stat

 

[krispy97xlt]

No need to show us the data lol taking it farther than ya need to. Thermostats are cheap and easy, I say go ahead and replace it again. 99% sure it's bad and you're just wasting gas driving around with a bad stat

Well after replacing my t-stat less than a month ago I was pretty sure it wasn't the thermostat.

I went ahead a sourced a replacement, pulled the old thermostat out and waited for my wife to leave the house.

Once she was gone I pulled out one of our nice kitchen pots filled it with water and placed both thermostats in the water and proceeded to heat up the water.

I monitored the water temp with a hand held IR thermometer...both thermostats opened up at the same time (+/- a few seconds) I pulled them out with some tongs and placed them in a bowl of cool water. They both closed.

Result: Inconclusive both appear to be functioning correctly.

Just for kicks I put the new thermostat back in the truck and buttoned her back up.

Wouldn't ya know it....with the new thermostat installed the truck climbed quickly to the correct operating temp, the thermostat opened, ECT dropped as it should and the process repeated.

I think both thermostat's were "good" however I think it might be possible that the previous thermostat was not sealed well in the housing and thereby leaking giving the indication of a thermostat that is failed "open".

At any rate thanks for all the help guys!