Thermostat issues?

[Gsmblue]

An odd one has occurred the last few days. Espy has been driving really well, but this strange phenomenon has occurred.

When I start her, I let her warm for a few mins before driving. Then when I am a few miles in I can see the temp gauge moving right. It will get almost to the H and then suddenly start moving back to the left to end up in the middle where it usually is. It may do this again once or twice. I have never noticed the needle getting so far to the right before.

Is this a sign of a failing thermostat?

[Gary Lewis]

What gauge is doing this? Stock or aftermarket? I ask because the stock gauges are very slow to react as they are damped significantly due to the way they work. So I would be surprised if a stock gauge would "suddenly" move in any direction.

But aftermarket gauges can do that as they usually don't have any damping. And in my experience you can usually watch the thermostat open and close on one of them, especially a mechanical gauge with a 270 degree sweep. So you may be seeing the engine warming up and then the 'stat opening.

If a factory gauge, you could also be having some issues with the instrument cluster voltage regulator - ICVR. It controls the fuel gauge, temp gauge, and oil pressure gauge. So watch all three of those to see if they are doing similar things. If so, the ICVR is glitching.

But, you may also be having a thermostat problem. Let's see what your answers to those questions are before we go there though.

[Gsmblue]

What gauge is doing this? Stock or aftermarket? I ask because the stock gauges are very slow to react as they are damped significantly due to the way they work. So I would be surprised if a stock gauge would "suddenly" move in any direction.

But aftermarket gauges can do that as they usually don't have any damping. And in my experience you can usually watch the thermostat open and close on one of them, especially a mechanical gauge with a 270 degree sweep. So you may be seeing the engine warming up and then the 'stat opening.

If a factory gauge, you could also be having some issues with the instrument cluster voltage regulator - ICVR. It controls the fuel gauge, temp gauge, and oil pressure gauge. So watch all three of those to see if they are doing similar things. If so, the ICVR is glitching.

But, you may also be having a thermostat problem. Let's see what your answers to those questions are before we go there though.

This is the stock gauge, and suddenly is a relative term! It is not instantaneous by any means.

All the other gauges are performing normally.

[Gary Lewis]

This is the stock gauge, and suddenly is a relative term! It is not instantaneous by any means.

All the other gauges are performing normally.

Then it may be a thermostat issue. As easy as they are to change I think I would if this trend continues.

But, is the radiator full? Obviously don't open the cap when the engine is even warm, but make sure that the radiator is full and that the overflow reservoir has coolant in it and that the hose is to the bottom. If not then you may have a bubble of air and that can cause swings in the gauge.

Getting air out of a cooling system can be done in a variety of ways. The fastest is to open the system at its highest point and bleed the air out. And the highest point on yours is probably the heater core. So to do that you'd pull a heater hose off the core and then fill through the hose until coolant comes out the top of the radiator and/or the heater core. Then re-install the heater hose w/o losing much coolant. But getting a heater hose off the core w/o damaging the core can sometimes be difficult.

Otherwise it is an iterative process of running the engine until it is fully warm and letting it cool, thereby pushing out the air while hot and sucking in coolant as it cools. But the radiator cap has to be up to snuff and the overflow hose has to always be down into coolant for this to work.

[Gsmblue]

Then it may be a thermostat issue. As easy as they are to change I think I would if this trend continues.

But, is the radiator full? Obviously don't open the cap when the engine is even warm, but make sure that the radiator is full and that the overflow reservoir has coolant in it and that the hose is to the bottom. If not then you may have a bubble of air and that can cause swings in the gauge.

Getting air out of a cooling system can be done in a variety of ways. The fastest is to open the system at its highest point and bleed the air out. And the highest point on yours is probably the heater core. So to do that you'd pull a heater hose off the core and then fill through the hose until coolant comes out the top of the radiator and/or the heater core. Then re-install the heater hose w/o losing much coolant. But getting a heater hose off the core w/o damaging the core can sometimes be difficult.

Otherwise it is an iterative process of running the engine until it is fully warm and letting it cool, thereby pushing out the air while hot and sucking in coolant as it cools. But the radiator cap has to be up to snuff and the overflow hose has to always be down into coolant for this to work.

Thanks Gary.

I checked the coolant yesterday, it is full in the radiator.

I will pick up a thermostat today and try and change it over the weekend. Hopefully it is straight forward, or that sailors language may make an appearance!

[1986F150Six]

Thanks Gary.

I checked the coolant yesterday, it is full in the radiator.

I will pick up a thermostat today and try and change it over the weekend. Hopefully it is straight forward, or that sailors language may make an appearance!

Is the temperature swing while driving at higher speeds? Have you replaced the lower radiator hose and did the replacement hose come with an internal spring?

[grumpin]

Is the temperature swing while driving at higher speeds? Have you replaced the lower radiator hose and did the replacement hose come with an internal spring?

I have watched my stock gauge go high and the aftermarket gauge stay at the same temperature.

[Machspeed]

This is the stock gauge, and suddenly is a relative term! It is not instantaneous by any means.

All the other gauges are performing normally.

Sorry to divert the topic, but I am curious about this ICVR you mentioned, Gary. My fuel gauge (I have dual tanks) is not working and my temp gauge, in the recent past, has reacted somewhat like the OP's. I noted a couple of weeks ago that it has now quit working. My oil pressure gauge does however work. Could this be the ICVR you mentioned?

 

 

[Gary Lewis]

Sorry to divert the topic, but I am curious about this ICVR you mentioned, Gary. My fuel gauge (I have dual tanks) is not working and my temp gauge, in the recent past, has reacted somewhat like the OP's. I noted a couple of weeks ago that it has now quit working. My oil pressure gauge does however work. Could this be the ICVR you mentioned?

 

If your oil pressure gauge works it isn't the ICVR as it feeds all three gauges. However, if you are curious about that you can read about it here: Documentation/Electrical/ICVR.

The page here tells how to test your gauges: Documentation/Electrical/Gauges and then the Troubleshooting tab.

It sounds as if you have two separate problems since the gauges quit at different times.

[Gsmblue]

Is the temperature swing while driving at higher speeds? Have you replaced the lower radiator hose and did the replacement hose come with an internal spring?

Yes i have, and what spring?!????