Wanted to get some thoughts on engine temperature issues I'm seeing. My water temp gauge gets extremely hot very fast (like buried into the orange zone within about 3-5 minutes of idle from a cold start), yet if I drive for 15+ miles my oil temp stays perfectly normal and below mid range of the gauge. Coolant reservoir is full, no steam coming from the engine, water pump is not leaking, fans and belts OK, hoses OK, overall runs fine, etc. It just does not seem water could heat up that fast and I do not see any side effects with engine overheating. I ordered a new temperature sending unit but it has not arrived yet. Any other thoughts on trouble shooting this?

 

Welcome first time poster! Do you happen to have one of those infrared digital temperature sensors that you can point to the thermostat housing after the gauge pegs? So you can see what the temperature is there? It might be that your water temp gauge is shot. What year is your car?

 

Thanks - it's an '81. I don't have an infrared sensor but think I can borrow one. I did notice the coolant reservoir stays at the "cold" fill line and does not really raise to the hot level. Could be that it's not circulating coolant. Maybe thermostat is stuck closed?

 

You shouldn't drive it until you figure out the problem. The infrared thermo is a good place to start. I would take out the thermostat and test in in a pan of hot water. Use a thermometer and bring the water up to the thermostat rating It should open. Have you done anything to the cooling system recently?

 

I haven't changed anything but I've only had the car for about a week. I thought it was a gauge issue, as the fuel sending unit also does not work and that needle is buried at a full tank (when I test drove and took it home the temp was as high as it would go). Think I will test the thermostat - and maybe just replace, as they are inexpensive. And I agree that holding off with driving is a safe idea until this is resolved.

 

You have a gauge problem would be my guess, if truly running that hot it would be puking out the overflow. A IR temp tester is cheap and a great tool for getting to the bottom of this issue.

 

You can test the gauge before pulling it out of the car... the lower picture below shows you the required inputs but you'd need an adjustable potentiometer to do this. If you don't have one you can use two old turn signal flashers in a series which usually will give you a reading of 50 ohms each (test before you do this). If you do use flashers and know the resistance of each (say 100) this should put your gauge close to the 200 degree mark. Using an adjustable pot is the best way because you just dial up the required ohms and test away.

But you can also test it without input ohms to the sender wire by following these simple instructions. (I know this isn't your gauge face but they all work on the same principle.

Pull the ohms wire from the sender and ground it out... turn the key on and your gauge should read like the picture in the upper left corner below.

Next, un-ground the wire and just let it hang. It should read like the gauge in the lower left picture.

If it works in this fashion the issue is the sending unit and not the gauge. If it fails this test you need a new gauge.

I have to say, I'm betting on the sender being the issue. The only issue this creates is that no replacement or reproduction sender sends the correct ohms to the dash unit. So if you replace the sender you might want to consider putting an adjustable resistor on the gauge and dial the gauge in to match the actual temperature of the car.






Here is a video link on how to install the adjustable resistor.


Willcox

 

Did he put tape or goop on the sender when he installed it? I would think that would just cause it to be off but not fluctuate you can try taking it out and see if anything is on it

when I bought my car it wasn’t working a d when I took the old one out I say tape and goop on it and I put a new sender In from zip with no problem and put a mr gasket radiator cap with a temp gauge on it to double check it

mine goes up to 180 and back down when the stat opens and fluctuates a bit around 190 when in traffic and cools down at higher speeds

 

Follow Willcox suggestions. Good info on the gauges. I'm sure that the gauge is not your problem. Either the sending unit is in error or the wire from the sending unit has "issues". I doubt that you will need to get into the gauge bezel area to successfully repair the real issues and get the temp and fuel gauges working properly.

 

You can also grab the upper radiator hose and see if it has pressure behind it. If the thermostat isn’t opening it’s not going to be that firm. The lower hose shouldn’t collapse at all due to it needing a spring internally to keep it from collapsing from the suction of the pump....it shouldn’t be going to over 280 degrees within 3 mins of starting without major issues so you probably are looking ata bad gauge...keep us updated