[allenga]

Guys, can you let me know your thoughts. I want to take this car on a road trip after I have been working on it for 10 months.

On today's 45 min drive, temp gauge was planted between the 220 mark and the next highest mark when going up hills or stopping.

65-70mph
All Highway
A/C On Max
96 degrees F
New cooling system (aluminum radiator, stock fan clutch, 180 thermostat, stock water pump, new hoses, belts, heater core).

Car ran fine, no smells.

Thoughts?

[Grand73Am]

First thing I'd do is use one of those infrared thermometers to aim at the radiator tank and see if it's really that hot. It's probably not, since you'd hear some boiling noises in the radiator.

You could also buy an inexpensive mechanical temp gauge from the parts store and install it and be able to see what the temperature really is too.

If you had a good spare original dash gauge, you could temporarily connect it to the temp sender wiring to see if the problem is your dash gauge or not. Or, of course, it could be an inaccurate sender unit too.

[goatless]

FWIW, my '79 TA sets pretty steady on the 220 mark on the factory gauge. I found it a little disconcerting when I first got the car, as I prefer to run quite a bit cooler than that. While I have never checked the factory gauges accuracy, I now assume that it reads high, based on experience and complete lack of issues- even when driven hard.

[TAKerry]

My 77 runs a bit on the high side as well, but its usually under 220. On one drive it spiked all the way and I had that moment of shear panick. I pulled over and did a visual inspection and the motor looked and sounded fine, and did not seem to be overly hot. So I took it easy on my way home. The next day I took it out and the gauge has been reading fine ever since. I marked it down as it being a 40 yo gauge that may be nearing its life span.

[77 TRASHCAN]

The infrared gun should tell you everything you need to know. I replaced my original water pump at about 50,000 preventatively. That was a mistake. With the stock water pump, the temp never got over 180. I had minor issues with it getting a little warmer with second pump, maybe 10 degrees warmer. I worked in a parts store. We got a new line of water pumps in. The Pontiac version was aluminum, cool, right? It didn't last too long, the bearings were cheap.
THEN, I read about the separator plate modification. Bought a new AC Delco pump (it does have the undesirable stamped impeller, though) it has been on engine for about 15 years now, and cools like the original, thankfully.
I believe your car is low miles and original. I wonder about the condition of your coolant? Cooling system may need flushed?

[allenga]

Originally Posted by Grand73Am

First thing I'd do is use one of those infrared thermometers to aim at the radiator tank and see if it's really that hot. It's probably not, since you'd hear some boiling noises in the radiator.

You could also buy an inexpensive mechanical temp gauge from the parts store and install it and be able to see what the temperature really is too.

If you had a good spare original dash gauge, you could temporarily connect it to the temp sender wiring to see if the problem is your dash gauge or not. Or, of course, it could be an inaccurate sender unit too.

Thanks Guys. Can I install a new aftermarket temp gauge to the stock sending unit, so have two temp gauges on the same sending unit? I replaced the stock sending unit by the way. No change in how the stock gauge reads.

[Grand73Am]

Originally Posted by allenga

Thanks Guys. Can I install a new aftermarket temp gauge to the stock sending unit, so have two temp gauges on the same sending unit? I replaced the stock sending unit by the way. No change in how the stock gauge reads.

The one I suggested to get is a mechanical gauge. So no, with a mechanical gauge. The thing I like about a mechanical gauge is there's no electrical to go wrong, since it works like a thermometer. You'd take out your sender unit. The mechanical gauge should come with a brass bushing to screw into the sender hole, and then the bulb end of the temp gauge tubing will screw into the bushing. If you don't want to go to the trouble of routing the gauge tubing and gauge face to the interior, you could secure it under the hood and after heating the engine up as before, you could pop the hood and see what the temp really is.

[allenga]

Originally Posted by Grand73Am

The one I suggested to get is a mechanical gauge. So no, with a mechanical gauge. The thing I like about a mechanical gauge is there's no electrical to go wrong, since it works like a thermometer. You'd take out your sender unit. The mechanical gauge should come with a brass bushing to screw into the sender hole, and then the bulb end of the temp gauge tubing will screw into the bushing. If you don't want to go to the trouble of routing the gauge tubing and gauge face to the interior, you could secure it under the hood and after heating the engine up as before, you could pop the hood and see what the temp really is.

Thanks Steve. I wish there was another port on the motor and I could leave the stock system in place.

[Grand73Am]

That's a good idea, so you can see both temps at once. Your temp sensor is in the head isn't it? Driver side probably?

There should also be the same hole for some kind of thermal sensor on the other head toward the rear. You could use that hole for the mechanical gauge.

[goatless]

You can add extra gauges if you want, but it would be a lot cheaper, quicker and easier to use an infrared thermometer like was mentioned by 77 Trashcan. You can check the temp at several points in the cooling system with pretty good accuracy without having to do anything more than point it and pull the trigger. Even the cheap ones from Harbor Freight are pretty accurate.
https://www.harborfreight.com/121-in...ter-63985.html

[tom s]

I check it at the tank where the water goes in from the engine and out to the engine to see what kind of temp drop your getting.I always look at it at the X over on each side of the head and also where the thermostat is.Tom

[allenga]

Some test results.

I live in the southwest. Lots of mountains and elevation changes.

If I drive on the highway with no elevation changes, 70mph, AC on, 88 degrees outside, etc., the car can remain cool according to the gauge, south of the 220 mark.

When I drive up in elevation, example from 1000ft to 2100 feet in elevation, the gauge goes north of the 220 mark, and when I get off the ramp and stop it goes higher.

I did the infrared temp gun measurements. When the gauge in the car was slightly north of 220, the temp on the temp sending unit was 230. The temp on the thermostat housing was 243. The radiator temp near the upper hose was 195.

I will run another test today.

[Peter Serio]

This is a very common problem with both the temperature gauge and the oil pressure gauges in 1960s as well as 1970s GM cars.


When GM made these gauges there is s small air space inside of the Nylon former. Inside of the air space at the very center of the nylon former (sealed inside of a lint, dust and dirt free chamber) rotates a small disc magnet. The pointer is connected to the disc via a very tiny shaft. Around the outside of the nylon former there is several 100 feet of small gauge wire wrapped in 2 directions; thus forms a 12 volt electro-magnet. The wire winding gives magnetic energy to move to the disc magnet in an arc. One winding tugs gently on the gauge pointer to move counter-clockwise and the other winding is wired into the car's harness and out to the sender. The sender string is connected from the #2 winding which causes these gauge to show increase. Be that either temperature and/or pressure. GM car gauges take advantage of the fact that electrical current will always seek the path of least resistance.

What I suspect has happened to your car is the air space inside of the nylon former; which was filled with a small amount of buffering fluid when it was made. (The fluid serves two purposes, one to give the pointer a smooth and steady reading and Two to act as a lubricant.) Over many years (seasons summers & winters) this fluid will eventually escape. It is designed to last the normal "life" of the car but it will not stay inside of the gauge forever. All older GM car gauges are subject to failure if the car is kept in running condition many years past it's first "lifetime."

Once your buffering fluid is gone, every time you start your car the pointer violently over-reacts due to the fact that these gauges are wired directly to 12 volts. Once this happens it is not reversible by a simple cure. At this point the gauge basically beats itself to death. The electrical part of the gauge is still working 100% however the pointer is no longer "indexed" correctly to the disc magnet. At first this will cause the gauge to read inaccurately. Over time it gets worse until finally the pointer simply falls off.

The electrical sender for a GM car (coolant temperature) with factory in dash gauges is a thermister. It is a 100% sealed unit and it is non-adjustable. There are no moving parts inside one of these temperature senders so there is nothing that can ever "wear out." Those will last for 50 or 75 years, or longer. If you have the factory original AC delco sender on your engine there is no reason that one of those should ever need replaced. With the exception that you have one that is not correct for the year of your car, meaning the gauge. Often engine re-builders love to install a new modern replacement aftermarket temperature sender. Warning!!!!!!!!!! : many of these type parts are NO LONGER made to GMs original specifications.

The cure for your issue is going to be that you will need to replace the gauges: Your temperature gauge and oil pressure are made as one assembly.

It is also very possible that your gauges can be repaired. I work on older GM car gauges every day. You can always PM me for more info.

[allenga]

Originally Posted by Peter Serio

This is a very common problem with both the temperature gauge and the oil pressure gauges in 1960s as well as 1970s GM cars.


When GM made these gauges there is s small air space inside of the Nylon former. Inside of the air space at the very center of the nylon former (sealed inside of a lint, dust and dirt free chamber) rotates a small disc magnet. The pointer is connected to the disc via a very tiny shaft. Around the outside of the nylon former there is several 100 feet of small gauge wire wrapped in 2 directions; thus forms a 12 volt electro-magnet. The wire winding gives magnetic energy to move to the disc magnet in an arc. One winding tugs gently on the gauge pointer to move counter-clockwise and the other winding is wired into the car's harness and out to the sender. The sender string is connected from the #2 winding which causes these gauge to show increase. Be that either temperature and/or pressure. GM car gauges take advantage of the fact that electrical current will always seek the path of least resistance.

What I suspect has happened to your car is the air space inside of the nylon former; which was filled with a small amount of buffering fluid when it was made. (The fluid serves two purposes, one to give the pointer a smooth and steady reading and Two to act as a lubricant.) Over many years (seasons summers & winters) this fluid will eventually escape. It is designed to last the normal "life" of the car but it will not stay inside of the gauge forever. All older GM car gauges are subject to failure if the car is kept in running condition many years past it's first "lifetime."

Once your buffering fluid is gone, every time you start your car the pointer violently over-reacts due to the fact that these gauges are wired directly to 12 volts. Once this happens it is not reversible by a simple cure. At this point the gauge basically beats itself to death. The electrical part of the gauge is still working 100% however the pointer is no longer "indexed" correctly to the disc magnet. At first this will cause the gauge to read inaccurately. Over time it gets worse until finally the pointer simply falls off.

The electrical sender for a GM car (coolant temperature) with factory in dash gauges is a thermister. It is a 100% sealed unit and it is non-adjustable. There are no moving parts inside one of these temperature senders so there is nothing that can ever "wear out." Those will last for 50 or 75 years, or longer. If you have the factory original AC delco sender on your engine there is no reason that one of those should ever need replaced. With the exception that you have one that is not correct for the year of your car, meaning the gauge. Often engine re-builders love to install a new modern replacement aftermarket temperature sender. Warning!!!!!!!!!! : many of these type parts are NO LONGER made to GMs original specifications.

The cure for your issue is going to be that you will need to replace the gauges: Your temperature gauge and oil pressure are made as one assembly.

It is also very possible that your gauges can be repaired. I work on older GM car gauges every day. You can always PM me for more info.

Thanks Peter. I am sure my gauge is off but based on my test it seems my car can't handle going up long grades.

[allenga]

Today's drive.

65 MPH
98 degrees F outside air
Flat road
Some stop and go.

Temp gauge 220+ indicated.

Temp Gun Test:

Upper Radiator 145F
Lower Radiator 185F
Thermostat Housing 235F
Temp Sending Unit 213F


I hit stop and go and the temp was nearly pegged. Should I replace the temp gauge or upgrade water pump.

[allenga]

Today I installed a mechanical temp gauge and surprisingly, the stock gauge is pretty accurate.

I drove for one hour, city and highway, with the AC on and off. The car ran between 200 and 234 degrees F.
On the highway, flat road with AC, car ran between 200-220.
On a steady grade, car got up to 230 on the freeway. When I stoped at the exit ramp, temp continued to rise up to 232 F.
Sitting in McDonalds Drive through, car got up to 234 F.

For running in the desert, is this car running hot in your view. Should I do anything about this.

I have no other symptoms. Car runs great.

Thank you!

[Grand73Am]

I'm very surprised at the high temps you're running. My opinion is there's something wrong. With the 180* t-stat that you have, I'd expect temps to be below 200* when warmed up at all times. 220-230's would not be acceptable to me, so I'd start looking for for reasons why it gets so hot.

I haven't experienced that problem, but have read about others who have. I remember a couple of fixes that was said to work. A common one is clearancing the water pump fan with the plate that mounts behind it to minimize the gap between the two. Also, in the same area, there are supposed to be 2 water pump sleeves. Photo below. Are you sure they were installed? If not, that would cause a big problem. The other was sealing the space around the fan shroud where it meets the radiator, so the fan pulls air better thru the radiator. They used some foam rubber type of weatherstrip to fill the gaps. Are you running a 7 blade factory fan?

s-l1600 by grand73am, on Flickr

[allenga]

Originally Posted by Grand73Am

I'm very surprised at the high temps you're running. My opinion is there's something wrong. With the 180* t-stat that you have, I'd expect temps to be below 200* when warmed up at all times. 220-230's would not be acceptable to me, so I'd start looking for for reasons why it gets so hot.

I haven't experienced that problem, but have read about others who have. I remember a couple of fixes that was said to work. A common one is clearancing the water pump fan with the plate that mounts behind it to minimize the gap between the two. Also, in the same area, there are supposed to be 2 water pump sleeves. Photo below. Are you sure they were installed? If not, that would cause a big problem. The other was sealing the space around the fan shroud where it meets the radiator, so the fan pulls air better thru the radiator. They used some foam rubber type of weatherstrip to fill the gaps. Are you running a 7 blade factory fan?

s-l1600 by grand73am, on Flickr

Thanks Steve. You know the water pump is the only thing I did not replace myself. I had a shop do it cause I was in a hurry so I don't know about the points you mentioned. I guess I will be taking it apart now.

[Grand73Am]

If you're not familiar with what "water pump to divider plate clearance" is, you can do a search for that phrase and there are many threads about it. Then see if any of them relate to your problem. It's one of the possibilities for improved cooling. I've never had to do it, but mine aren't higher performance engines that run hotter.

[Old Goat 67]

Originally Posted by allenga

Today I installed a mechanical temp gauge and surprisingly, the stock gauge is pretty accurate.

I drove for one hour, city and highway, with the AC on and off. The car ran between 200 and 234 degrees F.
On the highway, flat road with AC, car ran between 200-220.
On a steady grade, car got up to 230 on the freeway. When I stoped at the exit ramp, temp continued to rise up to 232 F.
Sitting in McDonalds Drive through, car got up to 234 F.

For running in the desert, is this car running hot in your view. Should I do anything about this.

I have no other symptoms. Car runs great.

Thank you!

IF THAT GAUGE IS ACCURATE also.

Sorry if this disturbs anyone, but that temp is borderline big time trouble!
180° thermostat, AC on in 95° temp, CORRECT water pump (no plate bending), CALIBRATED gauge and sender, highway or city, my car never gets over 187°.

Charles