Why would temp gauge swing up then back down?

[TechnoLoGs]

Originally Posted By: OVERKILL
Originally Posted By: TechnoLoGs
Originally Posted By: demarpaint
My Aerostar had the exact same symptoms twice, both times I changed the thermostat and the problem was resolved. I found the thermostat would last between 4 or 5 years in that vehicle, and I learned to only use Motorcraft thermostats in it. I did not have an electric fan, mine was belt driven. YMMV


Sounds like another T0stat change is in order.

I am now alarmed, because this also was changed by the guy, and they had to re-do the VSS, and it works now.. Less jerky, but still suspect...

I wonder if he put it in backwards, it IS a fail-safe.

And just two weeks ago, the temp was in the normal range, and I asked why it fluxuates WITHIN the normal range. This is weird.


If the speedo is "bouncing", that's not the VSS and is the speedo cable "catching" in its lining. So you either need to replace the speedo cable, or fab up a way to lubricate it so that it smooths out. My '87 Mustang had this problem, I just replaced the cable. Problem solved.


Makes sense! That speedo cable has been put through Hades.

I also suspect stray voltage of some kind.. Almost like the car sometimes hesitates and labors, then runs fine. The alternator was putting out 14V even a few weeks ago.

Could it be time to replace the alternator? Especially if it contains my voltage regulators, and rectifiers?

This alt looks pretty original, and we took the original VSS off yesterday.. Starting to think maybe things are failing gradually..

(This just guesstimation, checking in with the experts. I know some of my theories draw gunfire.)

 

[armos]

Originally Posted By: TechnoLoGs
Originally Posted By: OVERKILL
Originally Posted By: TechnoLoGs
Mine stays down close to the bottom of the gauge for extended periods of time, and only sometimes rises to the middle of but not over the middle of the gauge, with no real common denominator from when it does that.

It MAY rise to the middle when on the highway but sometimes it doesn't even do that.

today it almost never got off the line on top of the C mark!


That sounds like the T-stat not working correctly.


I do agree with you, the only thing is that we just changed it a week ago and this symptom continues!

Is it at all possible that the cooling system is soo stopped up that nothing short of putting a garden hose in and running it until the water runs clear will help things?

A clogged up cooling system can't cause overcooling. But if you think it's gunked up then I'd still flush it out with a hose.

You might want to make sure the gauge works correctly. I don't know how Ford does it but the temperature sender probably works on resistance. There might be a chart somewhere showing how many ohms of resistance represents a given temperature. You can plug a resistor into the connector and make sure the gauge is responding correctly.
Look for some info about your car's coolant temperature sender to verify the pinout and how it works.
You'll also have to make sure you find the right connector - the sender for the dashboard gauge is probably not the same one that talks to the ECM.

 

[armos]

Originally Posted By: TechnoLoGs

I also suspect stray voltage of some kind.. Almost like the car sometimes hesitates and labors, then runs fine. The alternator was putting out 14V even a few weeks ago.

At least on older GM alternators, from what I recall they regulate their output at 14.3V while running, as measured at the alternator. It will be lower elsewhere.

You shouldn't see any "pulsing" headlights and gauges though. I can't remember if you said that was happening on your car or not, I just remember the subject coming up.

 

[TechnoLoGs]

Originally Posted By: armos
Originally Posted By: TechnoLoGs

I also suspect stray voltage of some kind.. Almost like the car sometimes hesitates and labors, then runs fine. The alternator was putting out 14V even a few weeks ago.

At least on older GM alternators, from what I recall they regulate their output at 14.3V while running, as measured at the alternator. It will be lower elsewhere.


I took my reading at the battery terminals with a digital multimeter.

The symptom I have is intermittent "wahwahwah"-ing of RPMs.. No real rhyme/reason.

It does so MUCH MUCH LESS NOW, with the new and proper VSS for an AX4N, not AX4s. But there is still some gremlin (graemlin?)

My alternator DOES charge,
My battery IS new,
it HAD 12.4V "resting" voltage"
.. It has been suggested that these are a touch on the low side, and, with all this heat.. maybe I should replace alternator. It looks original.

I cleaned the connector up yesterday, with Brake Parts Cleaner.

?

Quote:
You shouldn't see any "pulsing" headlights and gauges though. I can't remember if you said that was happening on your car or not, I just remember the subject coming up.


I have not dine the "poor man's crank test" But I can tell you that the starting system works well. No pulsing lights, AFAIK. DID have a starter replaced.. I am unsure if timing could have been affected, it runs really well.. Sometimes it starts faster than others, sometimes I can turn the key and it starts instantly, sometimes I hear 4 rapid revolutions THEN it starts, in the morning maybe 6 or so at most.. Very fast, starter is new.. But, the car is acting "better."

Thinking a work speedo cable cant cause what I am experiencing.

Also, there ARE some that feel this is/was a flood car, so if my alternator got flooded.. but then, how would it work at all?

So, I have suspicions, but nothing concrete. it runs pretty good, most the time. Only sometimes doe sit labor and hesitate.

 

[Quattro Pete]

Originally Posted By: armos
Originally Posted By: Quattro Pete
Originally Posted By: SteveSRT8
Typically you see swings on an otherwise healthy vehicle because the electric fans are doing their thing.

Yup, that's what I believe is happening on my car. When I gun it, the electric fan kicks in.


The swings you're seeing go well below the thermostat threshold though, unless your thermostat is a lot colder than usual. It looks more like a case of the thermostat not closing quickly under a WOT scenario.
If you were able to maintain WOT for much longer, it should ultimately stabilize back in the intended range after the thermostat has time to react.

It's a 97C thermostat. After I replaced it with a new one, the new one behaves exactly the same way as the old one did.

 

[Errtt]

All my vehicles with temp gauges come up to mid point and stay there. Only exceptions was a few vehicles back around mid 80s to earlier. One vehicle got a new water pump, thermostat, hoses, later a radiator and although it still ran up & down, one year I put on a new radiator cap and it suddenly was only half as bad.

Today I got caught in a little backed up traffic (3 car accident) and sat in triple digit temps for what seem about 15-20 minutes with AC on. This was after about a hour driving. The temp gauge never moved from mid point. Then got home only (few miles away) to see it was 109 temp out in backyard shade.