I'm still having a problem with my gauge showing a hot condition at certain times. I posted about this before and we decided it was probably a ground problem.

What's happening is the temp gauge will go up very high (like 230 and it's actually pegged a couple times) then it will show that it is cooling down rapidly (like the thermostat just opened). This will happen under any conditions (recently started, ran for 2 hours, slow speed, idle, highway speed). The engine does seem hotter but it's never actually boiled over or steamed from under the hood when it shows it's hot. It has spit out a small amount of coolant. After it cools down it only takes a couple ounces to fill. So I'm not sure if it's really getting hot or just the gauge is showing it is getting hot.

Here's what I've done so far:
- Changed thermostat twice
- new fan clutch
- cleaned all grounds
- added 6 new ground wires and straps
- new sending unit

All components are brand new so there's nothing dirty.

I am missing the expansion tank and the foam around the radiator. The problem did not exist hen I first got the car so I've been ignoring those possibilities.

So, any ideas on what could be happening here?
My sending unit is located under the drivers side exhaust manifold, is that correct?

Thanks!!

 

Water pump??? Clogged radiator???

 

You need to find a shop with a IR, (Infra Red) gun and find out the actual operating temperature of your engine.

 

That's right your sending unit is on the driver's side below manifold. In additon to what Aaron added, did you check you hoses, make sure that they are not collapsing inside, try flushing your rad as well. You should get that foam back on as it will keep the air going through the rad instead of over/around it.

 

My car is doing something similar. Whenever I start my car, no matter how long it has been sitting, within 1/2 mile, no matter what speed or ambient temp, the guage swings up into the red, stays there for about 5-10 seconds, then falls to below 200, where it now stays.

When I first bought the car a few weeks ago, It seemed to run in the 220-240 range all the way down I95 from Boston to Fort Myers, FL. I checked for the foam around the radiator and it seems to all be in place. I replaced the T-stat and then flushed the system and replaced the 50/50 mix. Since then I haven't been out on the interstate, but around town it seems to stay around 195-200.

Current electrical stuff: I fixed a wiring problem to the alternator, not sure if it is ground or not. On top of the alt where the double connector plugs in, the brown wire had broken off.
At the moment, all my dash lights are out, but the guages (except the clock) all work. At the suggestion of some of the other members, I am going to get some alternative temp guage in place to check the accuracy of the one in the dash.

I bought an owner's manual that says not to do anything unless the guage reads 250 :rolleyes:

Don't know how much this helps, but I guess misery loves company. If I make any progress I'll let ya know.

 

Larry,
From what I've read, the replacement sending units are not calibrated the same as the OEM units 30+ years ago, and ALWAYS read hotter than correct temp. I've heard some are off 40 degrees. If that is the case, your thermostat might be opening at the correct temp, but the gauge is pegged too high "thinking" it is in the mid 200's.
Just a thought.

 

Hey Larry,
For a quick check I used a small digital thermometer in the expansion tank and watched the gauge. It was right on with the gauge, I then checked it with a calibrated thermometer from work and that was the same. With a 180* t stat the gauge stays on the first small line in front of the 210*. Does the car over heat in traffic,on the highway, or at idle? Did you change the carb or rejet it? I went through everything and found my carb was way too lean- the plugs were white.
good luck,
Gary :cheers:

 

Thanks for the help guys!

I just went out and flushed out the radiator, engine and heater core. They are all new and I didn't see anything even slightly off colored come out. That's good I guess!

I filled with straight water for right now (I've bought many gallons of coolant lately). I'll add some when I know I don't have to empty it again.

I let the car run and heat up with the radiator cap off. After the thermostat opened (160 deg but opened at 210 on my gauge) and I filled the rad, I watched the water shoot out of the radiator. So I'm thinking the pump must be pumping. It also doesn't leak like most of the bad ones I've had before.

I took it for a test ride and of course the same thing happened. I'm hoping the sending unit calibration / faulty reading theory is correct. I will take the advice and get an accurate reading on my temps. I wonder how much those infared things cost. That would be a cool addition to my tool box!

Thanks!

 

Hey Gary!

Nope, no real changes from stock. Possibly the timing could be off a little.
I havent really considered a carb factor.

The strange part is that it will happen under just about any conditions. Idle or at speed. It's just really strange!

Thanks!

 

Spoken like a true tool guy! :lol: :cheers:

 

In regards to the laser temp.---
I saw in Mid-Americas catalog they were $99 for a cheepee. That means about $75 in real world price :D

 

Ok, went and bought a Raytek infrared unit for under 100 bucks. It works great. I've taken all my employees outside body temp now. The ones I thought would be a little hotter actually were!!

Anyway, depending where you point the beam, it appears the gage is reading accurately. Of course I was unable to get the car hot this morning so I still don't know for sure. I'm going to carry the tester with me so when it shows hot next time I can jump out and test it.

I'm going to put the expansion tank from the 71 on the 69 to see if it helps. The fact that I can't get it to get hot this morning makes me think it has something to do with refilling the radiator last night. Possibly it does not have to be very low to cause an intermittent problem??

 

This excerpt from your post speaks volumes. I think you may have the sending unit problem mentioned here by Shoptek. Good luck! :cheers:

 

When I bought a new sender for my ZZ4 from NAPA it read off by 50 degrees. I found this out by watching the gauge and placing a thermometer in the expansion tank. My gauge was reading 230 degrees and the thermometer read 160. When my guage pegged out around 250-260 the thermometer only read 180. I eventually just placed the old sender back in and my gauge has worked perfectly since then.

Mark B.

 

Larry - When does it give a high temp reading? High speed driving or stoped?

 

It will do it at any speed under any conditions. That's why it has me stumped.
I put a new water pump on last night but haven't tested it yet.
Hopefully....

Larry

 

What you might have is an air pocket in the engine block.This happens alot when draining and filling small block chevies.The best way to fill small block is remove the t-stat and fill the block so that t stat housing if full of water.Then reinstall t stat and fill radiator the rest of the way up.
I had my 89 L98 flushed and dang if it didnt get an air pocket and ran hot till I did the above with it.

 

I hope you mean shoot out of the radiator fins into the expansion tank...

It the water actually came out of the filler cap you have a problem!

 

isosceles

If the gauge was accurate and you got to 250, by that time the oil is 300+ and braking down, and the tranny is cooking. That's my .02

 

Yep get to a radiator shop and have them use the temp gun on the T-stat housing and the radiator inlet and the back of the intake manifold to see what your water temp is at idle and actually coming out of the engine. Also, check the lower hose to see what is going back in the engine. You need at least a 30 degree drop to cool the block.

As far as checking it out on the road, do you have the temp sender in the block on the passenger side for emisssions? If yes, use that one for a mechanical gauge. If not you could remove the sender for the gauge temporarily and install a mechanical temp gauge, run the line inside the car to verify the engines temp range. They are about $15 and about a $1 for the adaptor fitting. Then you will know the temp when running.

The temp guns are as low as $69 in the auto stores now and it is well spent. I have had one for several years and use it on all the cars around the house, the BBQ grill, the oven etc. The uses are many.