1988 Plymouth Reliant - thermostat?

I had trouble with my 1988 Plymouth Reliant overheating in the spring. Replaced the thermostat and the problem went away. It was fine until the weather here started to get cold again and then it started acting up. When the weather is good the temperature gauge showed a normal temperature, when it gets really cold outside, it seems that the thermostat starts to stick.

I'm figuring I've got a faulty thermostat and need to just replace it. The symptons are exactly the same as the last time I was having this trouble and a new thermostat fixed the problem.

I checked the anti-freeze level and it's good and it looks clean also. The rad fan is functioning and the oil is clean, so no anti-freeze leaking into that or anything. Not sure if there's anything else that I need to check.

Has anyone heard of this problem before? I thought that if a thermostat was faulty, it would give you grief in the hot weather, not the other way around???

Rob.

First, lets recap what a thermostat does, so we can all start with the same understanding. This device is a valve that opens and closes based on the temperature of the coolant. When functioning correctly it is closed when below the preset temperature and open at or above the preset temperture. Therefore, below the preset temperature, the closed thermostat prevents water circulation in the cooling system. Above the preset temperature, the open thermostat allows water circulation. (I'm sure someone out there can describe in detail just how this device opens over a range of temperatures, but I am trying to keep this simple.)

Now, the thermostat has TWO modes of failure. One mode is that it sticks closed and fails to open. The other is that it sticks open and fails to close. When the thermostat fails closed, your engine will overheat, pegging to full H within the first few miles of operation. When the thermostat fails open, your engine will not warm up and your temperature gauge stay at or near C.

I have experienced both types of thermostat failures during my history of car ownership. I have also experienced other overheating conditions that appeared at first to be a bad thermostat, but turned out to be something else. I suspect the latter may be what you are experiencing.

Now, we need to know just what your temperature gauge is doing. I assume that it starts out at C when you first start the car. What does it do after that? Once I know how your cooling system temperature varies, I can better understand what is going on inside your engine. Please reply back with this information.

When I start the engine to drive to work the temperature gauge starts off at cold and it slowly warms up. This is all normal. Then after driving for almost 15 minutes (this is all city driving) instead of the temperature gauge staying in position at about 1/4 of the way up, the gauge will continue to climb until the time I get to work and shut the engine off at which point today it was about 3/4 of the way up.

I also took it for a little drive during a lunch break to get some gas. Drove to the gas station and everything was okay. Left the gas station to drive back to work and I gunned it a little to see what would happen. The temperature gauge climbed more rapidly and I had my heat on and it was blowing cool air even though the temperature gauge was about 3/4 of the way up. Arrived at work, left the engine running and popped the hood. The rad fan wasn't turning, although at this point I don't feel that's the problem. I'm pretty sure the rad fan works. The engine felt cool to touch. The antifreeze level in the overflow was fine and it looked clean.

The only reason I believe it could be the thermostat is because I was having the same symptons back in the spring, but then again, logically I believe the engine should be hot and it wasn't. Maybe the sensor???

Thanks,
Rob.

When I start the engine to drive to work the temperature gauge starts off at cold and it slowly warms up. This is all normal. Then after driving for almost 15 minutes (this is all city driving) instead of the temperature gauge staying in position at about 1/4 of the way up, the gauge will continue to climb until the time I get to work and shut the engine off at which point today it was about 3/4 of the way up.

I also took it for a little drive during a lunch break to get some gas. Drove to the gas station and everything was okay. Left the gas station to drive back to work and I gunned it a little to see what would happen. The temperature gauge climbed more rapidly and I had my heat on and it was blowing cool air even though the temperature gauge was about 3/4 of the way up. Arrived at work, left the engine running and popped the hood. The rad fan wasn't turning, although at this point I don't feel that's the problem. I'm pretty sure the rad fan works. The engine felt cool to touch. The antifreeze level in the overflow was fine and it looked clean.

The only reason I believe it could be the thermostat is because I was having the same symptons back in the spring, but then again, logically I believe the engine should be hot and it wasn't. Maybe the sensor???

Thanks,
Rob.

I would put in a new thermostat to be on the safe side.
But one thing to consider is when the air cond/defrost is on the rad fan will run all of the time and the engine should hold the thermostat tempt.
With just the heater or heater /ac off the engine will get up to around 225 degrees before the fan kicks on.
Turn the air cond or defrost on and see if the rad fans runs and see what the heat gauge does.
Also pull the rad cap and make sure the rad is also full of coolant.
The over flow could have coolant and the rad could be low if rad cap is not working good.
With ac off warm the engine up good to around 3/4 tempt gauge and speed engine up over 1000 rpm and make sure the rad fan kicks on at around 225 degrees.

An update ...

Was driving home last night in the snow and -10C temperatures - so as you may imagine the traffic was slow, which unnerved me slightly.

Noticed the temperature gauge slowly climbing and not dropping at all. Also noticed that the heat from the vents was not as hot as it should be. It was as if everything in the car was fine except for the reading on the temperature gauge. Was caught on a busy road and the temperature gauge climbed to the top. Pulled over at the first opportunity and left the car running and popped the hood to see what was going on, when, before I got out of the car the temperature gauge slowly dropped down back to its normal temperature.

I still checked out under the hood and the engine was cool, the tube carrying the antifreeze from the engine through the rad felt hot, but not so hot that I couldn't touch it. The rad felt cool. The antifreeze overflow level was about an inch and a half over the max line - this was the only thing I found a little odd. Maybe it was always like that.

Anyway, I got back in the car and drove the almost 10 minutes it took to get home and the temperature gauge was normal and regulated the rest of the way. Got home, popped the hood and everything still felt cool and the rad fan was on - fresh confirmation that that works.

Drove to work this morning and the temperature gauge was completely normal. The car has driven fine the whole time ... the only issue is the temperature gauge and today it stayed down in the normal range.

Could the thermostat be fine and the problem (I did replace it in the spring) causing me this grief be a blockage somewhere? If so, would a rad flush solve the problem or indicate to me whether something causing a blockage?

Thanks for the responses!
Rob.

An update ...

Was driving home last night in the snow and -10C temperatures - so as you may imagine the traffic was slow, which unnerved me slightly.

Noticed the temperature gauge slowly climbing and not dropping at all. Also noticed that the heat from the vents was not as hot as it should be. It was as if everything in the car was fine except for the reading on the temperature gauge. Was caught on a busy road and the temperature gauge climbed to the top. Pulled over at the first opportunity and left the car running and popped the hood to see what was going on, when, before I got out of the car the temperature gauge slowly dropped down back to its normal temperature.

I still checked out under the hood and the engine was cool, the tube carrying the antifreeze from the engine through the rad felt hot, but not so hot that I couldn't touch it. The rad felt cool. The antifreeze overflow level was about an inch and a half over the max line - this was the only thing I found a little odd. Maybe it was always like that.

Anyway, I got back in the car and drove the almost 10 minutes it took to get home and the temperature gauge was normal and regulated the rest of the way. Got home, popped the hood and everything still felt cool and the rad fan was on - fresh confirmation that that works.

Drove to work this morning and the temperature gauge was completely normal. The car has driven fine the whole time ... the only issue is the temperature gauge and today it stayed down in the normal range.

Could the thermostat be fine and the problem (I did replace it in the spring) causing me this grief be a blockage somewhere? If so, would a rad flush solve the problem or indicate to me whether something causing a blockage?

Thanks for the responses!
Rob.

I would put in another stat to start with.
MT

Thanks for the advice. My gut feeling was telling me to replace the thermostat to see if that fixes the problem, just checking to see if that seemed like a reasonable thing to start off with considering the symptons.

Seeing as I unfortunate to not have a garage and it's very cold and we're in the middle of a snowstorm here, I'll have to hold off for a bit or borrow someone's garage to do the job. I have the part though!

I'll let you know how I get on.

Thanks again for the reassurance and advice!
Rob.

Thanks for the advice. My gut feeling was telling me to replace the thermostat to see if that fixes the problem, just checking to see if that seemed like a reasonable thing to start off with considering the symptons.

Seeing as I unfortunate to not have a garage and it's very cold and we're in the middle of a snowstorm here, I'll have to hold off for a bit or borrow someone's garage to do the job. I have the part though!

I'll let you know how I get on.

Thanks again for the reassurance and advice!
Rob.


10-4 even a brand new stat can be bad.
You might try another brand or a major brand stat.
OEM or gate's are good ones most of the time.
Let us know how it goes.
MT

True ... I'll keep you posted. Hopefully I'll be able to change it out pretty quick (weather permitting). Thanks again.

Rob.

True ... I'll keep you posted. Hopefully I'll be able to change it out pretty quick (weather permitting). Thanks again.

Rob.

Here is a good tool to make sure your tempt gauge is working right.
http://www.calright.com/_coreModules/common/category
Detail.aspx?entityType=6&categoryID=66&gclid=CMrT9Lqk6ogCFRieWAodkzhWpA

When your tempt gauge reaches 195-200 degrees your thermostat should open and upper rad hose and rad should be hot to the touch and about the same tempt.
Then when it reaches around 200-225 degrees the rad fan should kick on and cool it back down to fan shut off temp around 200 degrees.
Or with ac on the rad fan should run when ac is on and hold tempt around 195-200 degrees.
Good luck and let us know how it goes.
MT

Here is one scenario that might be happening in your engine. This has happened to me in my 1991 Dodge Shadow 2.5L Turbo with 116,000 miles.

Last winter, the temperature gauge in my Shadow climbed to full Hot within three miles of leaving my house. I was on the freeway at speed when I noticed this and shut down the engine when I crested a small hill. Once I coasted safely to the side of the road and turned the key back on, the temperature gauge was reading normal again. This scenario played out two more times until I was able to stop the car, open the hood and feel the upper radiator hose while the gauge was still pegged on Hot. The hose was cold, indicating my thermostat was shut. I replaced the thermostat, even though it was only one year old.

After thermostat replacement, the scenario continued. Now, I know that the thermostats will fail to open if there is an air bubble behind it. This usually occurs only when refilling the system and not bleeding the air out properly before start up. But I bled my system correctly and drove the car without incident before this happened again. Thinking that somehow an air bubble was forming behind my thermostat, I removed it and drilled a small weep hole in the housing to allow for air release at start up. This trick cured this symptom and the strange overheat scenario has not returned.

In the subsequent weeks though, I began to notice a strong smell of antifreeze at times when the car was warm. But I could not find any leaks. After smelling the antifreeze again one day when I returned home, I kept the car idling in the driveway and opened the hood to see if there were any signs of leaks with the system hot and under pressure. I saw no leaks, but I did notice air bubbles erupting from the bottom of my overflow tank. When I removed the radiator cap, I saw the bubbles coming up from inside the radiator. Topping off the radiator and raising the engine RPM's caused the coolant to flow out of the radiator opening and it appeared to be mixed with small bubbles, like a carbonated soda.

I went down to my local independent (not a chain) auto parts store and asked if they had any way of testing the coolant for exhaust gas infiltration. They sold me a test kit called a "Universal Block Tester". This kit consists of a glass tube with rubber stoppers that you insert into the radiator cap opening, a suction bulb to allow you to draw air through the tube, and a bottle of blue test fluid that you pour into the tube to the preset level line. The tube has a sintered metal filter at the bottom to allow the passage of air through the fluid but restrict the flow of the blue fluid into the radiator. With the engine hot, the engine idling and the radiator cap off, you stick the tube in the radiator opening. You fill the tube with blue fluid to the line. Then, you either use the bulb to draw fumes from the radiator through the fluid in the tube, or just let the air pass up through the fluid by itself. If the fluid turns from blue to yellow within one minute of adding to the tube, then you have a combustion gas leak into the cooling system. Such leaks are caused by either a bad head gasket, a cracked head or a cracked block. When I tested my Shadow, the fluid turned yellow every time.

Here is what I suggest you do (Hopefully, you are a do-it-yourselfer, like me).

Remove your thermostat and drill a small weep hole in the metal plate. Any size from 1/16" to 3/32" will suffice. Then put it back in.

Next, warm up your car to normal operating temperature and see if you notice bubbles in the overflow tank. If you do, go to the auto parts store and buy a "Universal Block Tester". Follow the directions to see if you have a combustion leak, and if so, follow the detailed directions to determine which cylinder is the culprit.

Give this a try and let me know what you find. I think your problem may be a combustion leak, but you need to test this to verify. If this is not the case, we will have to think about this a little more.

It turned out, for me, that I had cracked exhaust valve seats on all four cylinders. I have since reworked the head on the Shadow, but I still haven't completely put it back together. Good luck with your car and let us know what happens.

Here is one scenario that might be happening in your engine. This has happened to me in my 1991 Dodge Shadow 2.5L Turbo with 116,000 miles.

Last winter, the temperature gauge in my Shadow climbed to full Hot within three miles of leaving my house. I was on the freeway at speed when I noticed this and shut down the engine when I crested a small hill. Once I coasted safely to the side of the road and turned the key back on, the temperature gauge was reading normal again. This scenario played out two more times until I was able to stop the car, open the hood and feel the upper radiator hose while the gauge was still pegged on Hot. The hose was cold, indicating my thermostat was shut. I replaced the thermostat, even though it was only one year old.

After thermostat replacement, the scenario continued. Now, I know that the thermostats will fail to open if there is an air bubble behind it. This usually occurs only when refilling the system and not bleeding the air out properly before start up. But I bled my system correctly and drove the car without incident before this happened again. Thinking that somehow an air bubble was forming behind my thermostat, I removed it and drilled a small weep hole in the housing to allow for air release at start up. This trick cured this symptom and the strange overheat scenario has not returned.

In the subsequent weeks though, I began to notice a strong smell of antifreeze at times when the car was warm. But I could not find any leaks. After smelling the antifreeze again one day when I returned home, I kept the car idling in the driveway and opened the hood to see if there were any signs of leaks with the system hot and under pressure. I saw no leaks, but I did notice air bubbles erupting from the bottom of my overflow tank. When I removed the radiator cap, I saw the bubbles coming up from inside the radiator. Topping off the radiator and raising the engine RPM's caused the coolant to flow out of the radiator opening and it appeared to be mixed with small bubbles, like a carbonated soda.

I went down to my local independent (not a chain) auto parts store and asked if they had any way of testing the coolant for exhaust gas infiltration. They sold me a test kit called a "Universal Block Tester". This kit consists of a glass tube with rubber stoppers that you insert into the radiator cap opening, a suction bulb to allow you to draw air through the tube, and a bottle of blue test fluid that you pour into the tube to the preset level line. The tube has a sintered metal filter at the bottom to allow the passage of air through the fluid but restrict the flow of the blue fluid into the radiator. With the engine hot, the engine idling and the radiator cap off, you stick the tube in the radiator opening. You fill the tube with blue fluid to the line. Then, you either use the bulb to draw fumes from the radiator through the fluid in the tube, or just let the air pass up through the fluid by itself. If the fluid turns from blue to yellow within one minute of adding to the tube, then you have a combustion gas leak into the cooling system. Such leaks are caused by either a bad head gasket, a cracked head or a cracked block. When I tested my Shadow, the fluid turned yellow every time.

Here is what I suggest you do (Hopefully, you are a do-it-yourselfer, like me).

Remove your thermostat and drill a small weep hole in the metal plate. Any size from 1/16" to 3/32" will suffice. Then put it back in.

Next, warm up your car to normal operating temperature and see if you notice bubbles in the overflow tank. If you do, go to the auto parts store and buy a "Universal Block Tester". Follow the directions to see if you have a combustion leak, and if so, follow the detailed directions to determine which cylinder is the culprit.

Give this a try and let me know what you find. I think your problem may be a combustion leak, but you need to test this to verify. If this is not the case, we will have to think about this a little more.

It turned out, for me, that I had cracked exhaust valve seats on all four cylinders. I have since reworked the head on the Shadow, but I still haven't completely put it back together. Good luck with your car and let us know what happens.

10-4 KManiac
Good idea.
I wondered about that when he said the heat quit on acceleration.
Another sign of head gasket leakage is heating up fast on heavy acceleration.
The old block/head gasket test would be a good test to run on it.:grinyes:
MT