Thermostat issues?

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?

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.

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!

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.

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.

1986F150Six wrote

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?!????

Some people say you should have a spring inside the lower radiator hose to keep the water pump from sucking it flat and stopping flow altogether.

I have a spring because my Gates hose came with one, but I have never seen it happen in a street driven vehicle.
After all, if there is 12-16 psi in the system how clogged would your radiator have to be, and how fast would you have to be turning the pump to defeat the bypass?

Interesting, thanks for that info. My lower hose is new and I have not notice it collapsing nor did I notice a spring in there...

What I did notice yesterday, as I had the Bronco on the driveway at idle as I was moving vehicles, after about 15-20 mins the needle got all the way to H on the gauge and I could hear a little radiator cap venting.

So I parked her and let her cool. I will change the thermostat out today and test the old one. I definitely have some issue here..

I checked the coolant level this morning and it was good. I have not checked the seep hole on the pump but I will get to that later too.

Yesterday was 94F so it was really hot out and bound to show any cooling issues...

Fun times...

Do you think 94F is "really hot"?

I mean, consider the delta.
The truck had no load on it and the fan should be pulling plenty of air through the radiator.

Do you have a good fan shroud?

I sweat at 88F!

Fan and shroud are in good shape. It was the first hot day of the year, i always find big temp deltas makes old trucks misbehave. I think it was 46F in the morning..

Hoping to finish work early enough tomorrow to deal with it

I've been working on new docks this week.
Beautiful views, but no a breeze has been brutal.

Just for S&G I brought my IR thermometer Tuesday, because I almost passed out from lack of electrolytes on Monday. (Had drank 7 liters of water, so I don't think I was too dehydrated)

Ipe deck boards were 152F, the black flotation tanks were over 200!
But I managed to pre drill and make my way through a couple of 25# tubs of 3" stainless screws.
I've no idea how hot the cleats and their 1/2 bolts were but their thermal mass was quite uncomfortable.
-Yes, I had it set on the correct emissivity-

Here's hoping you just have a sticky thermostat.
Be careful keeping it in place as you tighten up the housing.

Holy smokes! I would have wilted. I do great in the cold, practically thrive in it, but the heat makes me irrational.

Looks like I will have time today to pull the thermostat.

I have a new truck with similar issue. When I leave from work, it takes me about five minutes from startup to being on the freeway and if I have to floor it to get on the freeway, I see temps spike then settle down. Other than that the gauge is flat in the middle. My first idea is a sticky thermo. Once thats eliminated, troubleshooting can continue.

Sitting at idle will also cause higher than normal temps because theres no airflow and youre fan is running as slow as possible.
Stay cool!

This is why the Ford system has a thermal control valve that gives the distributor full manifold vacuum and steps up the idle if the coolant temperature rises too high.

A little spike when the engine is first being warmed up is not uncommon.
I find my truck runs right around the O in daily driving, but my instruments work differently than Bullnose.


.

ArdWrknTrk wrote

This is why the Ford system has a thermal control valve that gives the distributor full manifold vacuum and steps up the idle if the coolant temperature rises too high.

A little spike when the engine is first being warmed up is not uncommon.
I find my truck runs right around the O in daily driving, but my instruments work differently than Bullnose.


.

 Well, Jim, in that picture, the truck is certainly not idling!

No, but it's right on the 'O', where it always sits.  

That's dawn coming up behind me.
I guess I can't outrace the sun?