Temperature reading high

On to the next problem. High cooling temp.
The water pump is 2 or 3 years old with less than 1000 miles. Previous owner installed it.
I have flushed the system, burped it twice now, new thermostat, new temperature sending unit, and cleaned my very dirty ground from the motor to the frame.
I took it on about a 2 hour drive where I flogged it pretty hard on some twisty roads. The temp stayed at 195 or a little above. Once I had to stop and sit a few times the temp got to the mark after 195. The fans would kick in and the temp would come down to almost the middle. The drive home it stayed closer to the mark after 195. Today with it sitting idling it got close to the top of the scale before the fans came on.
When I saw what it was doing I checked several spots with my IR thermometer. The highest reading I got was 198. I checked every where. The middle of the V, the bace of the heads, all the water pipes, even where the temp sensor is, nothing was near that hot.
At the radiator the inlet would be about 195 and the exit about 170. Once the temp at the sensor got to about 198 the fans would kick in.
I trust my IR readings. I don't think the car is getting hot.
One time I wiggled the wire attached to the temp sensor and the temp reading came down. One of the reasons I changed the sender.
when I had it apart I check the resistance on all the wires that run through the common plugs. I did this because the oil pressure gage is interment.
Next I will pull the instrument cluster and see what I find.
Does anyone know of a chart with the resistance at the sending unit?
I think I have a wiring problem.
Any help would be great.

sorry for the length.
Lee

 

The tachs are not very accurate, the speedometers are not very accurate, the oil pressure gauges are not very accurate. In my experience the water temp gauge you can pretty much bet your life on. Reading temps on the outside of the hose or casting isnt a worthless exercise but its the next best thing.

Two really bad things for an aluminum engine, overheating it and cronically almost overheating it. It will turn the aluminum soft and the motor will become garage art. You are getting it into the territory I tell my clients to pull over and park it.

My suggestion is stop driving it until its figured out and fixed. It will not fix itself.

 

Verify the connections (esp on the ground side) in the instrument cluster.

You can get feedback from a flaky gauge into another gauge, causing one gauge to read high, the other low.

Someone here described how they took the cluster out and resoldered a bunch of wires and everything worked well afterwards.

Doug

 

Not all temp sensors are equal. The OEM sensor is the way to go. The cheap ones, often cross refereneced to a Volkwagn application, are of dubious quality. I had replaced with a cheap one, and the fans did not come on til too hot. A new OEM one (actually old stock in the F yellow box), and all is as it should be again.

Also, put some Redline Water Wetter in the coolant. It really does work, takes the temp down a bit by increasing the heat transfer from coolant to the metal in the system.

 

Is the 195 hash (the middle of the gauge) not a proper operating temp for a warmed-up car? I assumed it was.

Check your coolant tank cap - if it's worn and not sealing properly, it can lead to an overheating car. If it's the lower-bar version, it might be worth replacing it with a fresh, higher-bar one. The caps do fail more often than you'd think, and if the system isn't holding proper pressure, it significantly affects cooling.

 

I would really be interested to hear a fact based engineering explanation of how "feedback" (and reciprocal feedback to boot) occurs from one gauge to another, even though they are on separate circuits. Most gauges are fed 12 and grounded via a variable resistor (aka the sender) to provide the calibrated resistance which registers on the calibrated gauge, so not sure what grounds you are referring to. Overall your assertion makes no sense to me, but I'm always happy to listen to verified factual information.

 

The gauges get their power from the same battery,and use the same ground, in that sense, they are on the same circuit. Without looking at a wiring diagram, i can't tell you if each small cluster gauge has its own circuit via a fuse in the fuse box, or they get their power from one positive wire feeding all of them directly behind the cluster, which i believe they do

These gauges are voltage compensated, other wise they would read higher or lower depending on line voltage, alternator running vs alt not running for example. There are two coils in each gauge, sensor and compensator. Some gauges may even have three from memory, i am NOT a gauge design expert. I do know the closer things are wired together, the more they interact due to less ohms in a short section of wire connecting them vs long section (this is also why one wire alternators, are NOT the way to go, even though people claim they are so great, a separate subject,,,)

Bad grounds can either be the sensor ground, or the ground for the compensator coil. Or one can have less than optimal power connection to the compensator coils also, I suppose.

Electricity will take the path of least resistance, ohms in parallel are decisive, two 10 ohm resistors in parallel is the same as one 5 ohm resistor for same amp flow .

Gauge coils are resistors, if one compensator coil out of two in parallel has a bad ground, it will have a higher resistance, causing that gauge to read higher or lower than it should, it also will affect the other gauge (If it is close enuf, wiring wise), making it read differently also.

Perhaps the best illustration of a bad ground situation some may have noticed (on no particular car) is when operating the turn signals make one or mare gauge deviate in synch with the turn signal, the turn signal provides an alternate ground, or higher voltage source (feed back), to the fluctuating gauge, depending on how the vehicle is wired.

Doug

 

BTW, all of the above is my recollection of 51 YO auto mechanics electrical class, and having worked with 65 YO and more American cars and wiring. Italian, and certainly Brit wiring harnesses/electrical flow, I have noticed, has some differences. The last gauges I took apart were sometimes in the late 1980s.

Doug

 

LE06 - I feel your pain; struggling with highly fluctuating temps.

Back up to the basics before getting buried in gauge signal crossover noise feedback. Which thermostat did you replace the old with ($300 or the $50 version)? Does it have a burp hole? If so, is it positioned at the top? Did you purge the air out of the radiator? Did you open the heater cores before bleeding? Replaced the expansion tank cap?

I highly suspect these inexpensive replacement thermostats out there are complete garbage and could contribute to such temperature variability. I'll admit it, I've gone with many "same spec" alternate parts which cost a small fraction of a factory parts only for them to bite me back.

BTW... I was curious, so dug through my 328 manuals. Nowhere could I find a "normal or optimal operating temperature" value. It seems by those here on this forum, 167-195F is a normal range. (My car stays within those values, but does go up to about 210F in stop-go-traffic. And that drives up my anxiety.) However, here's the really important bit I found: the owner operating manual states, "... max permitted temperature is 230-240F (110-115C). It is necessary to reduce immediately the engine RPM in case the temperature exceeds 240F (115C)." I personally would be more cautious and take rifledriver's advice to immediately pull over and shutdown well before reaching 240F.

Additionally, the operator manual gives specifications for radiator fans on/off temps (On @ 183F, then Off @ 167F) as well as a vague range of when the thermostat valve begins to open: "176-185F, 80-85C".

The Technical Specifications manual (for 328) agrees with the owner operator manual by simply stating, "Max. Operating Temperature 115C (239F)."

Good luck and keep us posted on what gremlins you uncover. It's helpful to us all.

 

@Rifledriver I agree the IR is second best. I will take your advice and not drive till I find the problem. It does have me scratching my head.

@moysiuan I ordered the temp sensor from AWI, I hope its a good sensor. I will add some Redline Water Wetter.

@ZikZak I have a new .9 bar cap but I do have a new 1.1 bar i can put on the car.

@rwbolt1 I have the $58 thermostat I could order another one and give it a try. It did have the hole in it, I feel sure it is at the top. I may double check. I did purge the all the air out and the heater valve was open when I refilled the system.

I went back in the records I have of the car. The water pump was replaced in 2021 and has 1000 miles on it. When I did the timing belts I checked it. It was not leaking and the bearings felt very good. Maybe the implementation is crusty and not pumping well. I may pull it off and check it. Also I will double check I have the weep hole at the top on the thermostat.
Once I check all the mechanical parts I am going to t check the readings at the sensor with my meter then pull the instrument cluster. I have to find my intermented oil pressure gage problem anyway.

This sure is a head scratcher.

Thank very much for the help.

 

If the pulley is still turning and water is not leaking the pump is fine. As far as the hole in the thermostat?????? Factory put them in every which way. It makes no difference. When it opens do you really think all that water cares where the hole is????? Come on.

 

Yea pulley is turning and not slipping I checked to make sure the belt is tensioned properly. I thought perhaps it was slipping causing the problem. As far as the hole, it’s Italian, it may care….. You are right once the thermostat opens the hole should not matter.
What are your thoughts on ordering another thermostat?
I have water flow I know because the radiator has hot water coming in and cooler water going out. Also the heater worked fine, so the heater cores have water cycling through them. Unless the flow is too slow or I got a crappy thermostat it should not be getting hot.

 

Manual recommends, couldn't hurt and makes sense looking at the angle the thermostat sits to help with bleeding air especially on a cold engine when the valve is closed.
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If the bleed hole is positioned on the top of the thermostat during install, it does let the air out during static, cold bleeding. If the vehicle is at operating temp, I see no difference in position.

Thats what i always have done, it just makes logical sense.