1984 Gt Vert. Overheat

[Tcapper]

Hi, I had an unusual problem last night. I was out for a ride and almost home I looked down and the temp, gauge was pinned to hot. Stopped the the car immediately and checked under the hood. Nothing seemed overly hot. Babied it home by coasting and it seemed to go to normal a couple of times. I'm going to flush the system and replace the antifreeze. I bought the car about a month ago and it appears to have a new water pump and now wondering if it has an air lock or a faulty temp. sending unit (which I don't think is the case). Now a couple of questions, has this happened to anybody before and when checking, I noticed the overflow tube at the top of the rad filler seems to go into the washer fluid reservoir, is this normal. Any pics I've checked out all seem to be the same as mine. Any suggestions would be greatly appreciated. Thanks, Troy.

[vintageracer]

First off did the car overheat?

A "New" water pump is a possible indication that the previous owner may have experienced cooling issues.

Does the car still have the original copper core radiator?

Is the temp sending unit original or a replaced with a new one?

Try removing a heater hose and see if you can back fill the cooling system with any additional coolant.

Buy a hand held infrared temp gauge to see if your car is truly running hot.

With a little investigation on your part you should be able to determine the problem rather quickly with help here on the site rather than just blindly changing parts.

[Tcapper]

Don't know what was replaced before I bought the car, except the water pump looks new. I'll do a little more investigation and see what turns up. Thanks.

[JacksAO]

Did you noticed if the oil pressure and fuel gauges went to full scale reading also? If so the problem could be in the instrument voltage regulator mounted behind the instrument panel.

[Tcapper]

All gauges normal. I guess it'll be step by step. It will be figured out.

[Mgino757]

I used to have the same problem with my '85. Turns out, the wiring to the sender was not getting a good signal.

[Tcapper]

I have just topped up all fluids and cleaned all electrical connections with HFE electronics cleaner. Ran the car at just idle for about 1/2 hour( haven't taken it out yet) and kept checking levels, temp. etc., the gauge just sat at the low end of the normal scale. I've worked on a ton of cars in my life and have never seen this before, I don't believe that the car actually overheated, but going flush the rad and change oil for the sake of it.

[Mgino757]

I have just topped up all fluids and cleaned all electrical connections with HFE electronics cleaner. Ran the car at just idle for about 1/2 hour( haven't taken it out yet) and kept checking levels, temp. etc., the gauge just sat at the low end of the normal scale. I've worked on a ton of cars in my life and have never seen this before, I don't believe that the car actually overheated, but going flush the rad and change oil for the sake of it.

Sometimes all it is is a bad electrical connection. Good call, preventative maintenance is always a good idea.

[homer302]

These cars did that when relatively new. That is why someone above asked about the other gauges. Usually when the issue occurs, the fuel gauge and possibly others will peg for a couple minutes, then drop to normal. It sounds like you saw it "bouncing" because you said you thought it went back to normal a few times. It is impossible it could cool down that fast, suggesting an electrical/gauge issue. It may go months without doing it based on my experience and then do it often for a week and then quit again. Safest option is to get a REAL temp gauge just temporarily hooked up long enough for the OEM gauge to peg and then see what is REALLY going on. You are probably just fine.

[Matt J]

I always recommend a cheap $20 mechanical temp gauge that you can buy from any local parts store. Screw in the new sender in place of the old one (keep it so you can put it back in later if you want) and run the wire through existing holes in your firewall. Clip the gauge itself to the bottom of the passenger side dashboard (I used a big alligator-style paper clip). You can see the true temp of the car while you're running it, and you can see when it goes up and down and gives you a real reading of the internal temp of the car. The stock temp gauges are notoriously inaccurate. If you prefer the look of the original gauge, once you're comfortable that you have the temp situation under control you can simply hook up the old sender and move along!

[Tcapper]

Worth a try, I still haven't been able to take it out yet, but a buddy of mine had the exact problem with his Dodge Ram and after a pressure test which I haven't done yet, it proved out to be his water pump, but I am leading it to the gauge as is there were no visible signs of an overheat.

[slow84lx]

It may not really be overheating as already mentioned. A couple of things to check that could cause the erratic gauge reading that you are seeing.

1. Teflon tape wrapped on the threads of the sender. Use a paste sealant instead.
2. Check the wire to the sender well. The wiring on our cars was marginal when new and in most cases hasn't aged well. Cracks in the insulation grounding to the intake could cause the problem.

[Tcapper]

Finally got a good hot day 87 degrees to test. Bought an infrared thermometer and a coolant pressure test kit, no leaks, temperature remained constant at the center of the gauge (didn't take an actual reading). It seems that the last owner who owned the car replaced the water pump and didn't burp the cooling system properly. Rookie mistake, had air bubbles in the system. All good now. Thanks for all the help.

[mikestang63]

not to hijack but experiencing something similar
bought the car last month temp gauge didnt work and the fuel gauge didnt work
grounded out the sending wire on the temp gauge and it pegged to hot
replaced the temp sending unit and then driving the car the gauge went H within minutes
Reburbed the system again with a Lisle funnel- no air bubbles
replaced the temp gauge and also noticed the gauge ribbon not fully engaged in the electrical connections.
Now the fuel gauge works properly however after a few days of the temp gauge seeming to work fine it will creep up to H
car is not displaying any signs of overheating- even have a radiator cap with the thermostat built in . the temperature on the cap reads 170 with the gauge nearly pegged H. The car would be puking coolant and running poorly if the gauge was accurate.

Think I will just install a set of electric autometer water temp, oil pressure, and volt gauges and mount them in the car display area under the radio. LMR sells a 3 gauge holder for around $40 and be done with it.

[Matt J]

I like those things because they give you a good reading while you're in the car. I like the infrared thermometers, but you have to stop the car and get out of it to read it, the replacement gauge is in the car so you can see it in real time. Also, once you're comfortable that the car is running correctly, you can simply reconnect the old gauges and you know what "normal" is for your car. They used the same gauge package for many years with cars running different motors and thermostats. The "normal" that the temp gauge reads is going to be different for different setups.