Effects of thermostat stuck open?

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What are the long term effects of driving a vehicle that has the thermostat stuck open? Does this contribute to sludge due to a cold engine?
 
I changed my oil and ran about a half quart of MMO for about 500 miles. I received the Auto-Rx that I ordered, so I drained my oil and it was very black, which leads me to believe there is a lot of sludge in the engine. Since adding the Auto-Rx (along with changing the pvc, and thermostat), fuel economy seems to have increased.
 
"I have a 1991 Pontiac Sunbird LE (2.0). Neighbor purchased it when it had about 8k miles and it has only been driving in town. It has averaged about 4k miles per year over the past 19 years. I am averaging about 1k miles per month, so it sees a lot more driving. It currently has about 83500 miles.

When I purchased it a couple of months ago, the air filter was very clogged and dirty. I changed air filter, pvc valve, thermostat (which had been stuck open for who knows how long), oil filter etc... I added Auto-Rx and am about 1500 miles into a cleaning cycle. I drive six miles one way to work and average about 25 miles per day by the time I come home for lunch, run errands, etc.. I was averaging about 22 MPG for starters. Now, I am getting 25-27 MPG. Is it possible that the Auto-Rx is is cleaning the engine up and increasing fuel economy?
_________________________
Larry "

After knowing thermostat was stuck open, I would have done two or three less than 1K oil changes before starting the Auto-Rx.
To late now. Go with it!
Run it hard. Heat it up!
 
Originally Posted By: tomcat27
sludge, decreased gas mileage, increased engine wear.


I bought a V-8 Holden once, and diagnosed a stuck thermostat. Couldn't have been wronger, as a previous owner told me he threw the thermostat out as soon as the warranty was over.

45,000 miles later, the ridges on the front two cylinders were insane, and the valve guides stuffed.

Always run a thermostat that functions properly.
 
I had a car with a stuck-open thermostat for awhile; when conditions were cool enough it would keep the lockup torque converter from locking up. It was noticeable because right upon reaching highway speed, I'd feel it "downshift" and see a corresponding bump in RPMs on the tach. Too bad I didn't have a scan tool at the time, I'd like to know how cool the car was really running. 160 perhaps? I don't know.
 
Originally Posted By: tomcat27
sludge, decreased gas mileage, increased engine wear.


+1 and little to no heat in the winter. Change it, others might disagree, but if I were the OP I would get an OEM thermostat. I've had too many problems over the years with aftermarket thermostats. I only buy OEM when it comes to thermostats. JMO
 
Better stuck open than shut. This is why many thermostats default to open, if they puke.
But your coolant sensor will read cold, and run rich. Fuel wash in the cylinders will wear them, and the rings/pistons. Fuel will be wasted, of course.
This is the main bad thing. There are others.
 
The Jetta has an open thermostat from what i can tell. Runs pretty cold in the winter. This fall will be water pump and thermostat change for sure.
 
The t-stat stuck open on my 4.0 Explorer. It wouldn't get up to full operating temp, and the fuel economy sucked, but drivability was fine.
 
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