Temperature Sendor Replaced but running hot

[mightyatom]

Hi All,
This is my first post on the site although I have been reading up on a lot of the older posts since I got my 72 Chevy C10 (350ci) a week ago. My first job was to replace the water temperature sender (Autozone part) which got my temperature gauge working although at normal running temperature it is very near the top of the gauge (80% towards the top). I ran the car and made sure there was no air in the system and topped it up as it cooled so think air in system is not an issue.
It seems like the water pump is working as the car never maxes out the temperature gauge so I was thinking it may be the thermostat and plan on replacing it next. Is there anything else I am missing which would bring the temperature down to mid-range on the gauge or did these old trucks always run hot on the gauge ?

Thanks Jay

[ChevLoRay]

to the board!

If you have not replaced the thermostat, by all means, do so. There are cheap ones and there are good ones. Go for the good one.

After that, if you still think it is running hot, invest in a mechanical guage, if for no other reason than for your own peace of mind.

[Classic Heartbeat]

You can replace the thermostat, but I would find someone with a temprature gun to read the actual heat of your engine first. If your truck was overheating I would tend to think that the thermostat was the problem, but it doesn't sound like it is. It is just running hot, or at least you suspect it is. Your gauge is most likely the problem, or the wire leading to it. This is why I would get a real reading from a gun. WES

[neba]

the old guages are not real accurate.sounds like where mine reads.

[jim zag]

I had the same problem. I put a mechanical gauge in mine and the engine temperature was normal so I then put a new gauge in the dash and now it reads just fine.

[fdbdw]

I had the same issue, changed the sending unit and it pegged the gauge and everything was still cool to the touch, I changed the thermastat just to be sure and it still pegged, turns out the new sending unit was a different resistance. I found a NOS sending unit and everything was fine. Could be your issue

[Security guy]

Don't forget if you haven't already, flush out your cooling system as well. It needs to be cleaned from time to time anyways, and put a 50/50 mix of water and antifreeze. Don't run straight water because the antifreeze helps in keeping your motor cool as well as keeping it from freezing. I see alot of people run water and have heating problems.

[BLACK AND BLUE 67-72]

I have ran into the same problem, with my old sender my guage ran on the first mark past cold, except when pulling a load and then it might get a needle's width past that mark. I had to change the sender because the center actually popped out of the housing, I got the new sender in and now the guage reads about 1 needle's width from the mark before hot!! So I really think that the sender is the problem, wrong resistance causing the guage to read wrong.

[mightyatom]

Many thanks for all the replies.

1. I noticed the the braided earth strap on the bulkhead is not connected. Should this go somewhere to the block and could it cause an issue.
2. What does NOS mean. Is this a manufacturer ? I was dubious of the Autozone temperature sender I put in but thought what could go wrong !
I will order and NOS sender so I can change it the same time as the thermostat.
3. I did flush the radiator but not the system. Have not done that before so good thing to learn.
4. If all the above fails I guess I will move on to the temperature gauge itself.

Again, many thanks for the replies. For use newbie mechanics its a lifeline.

Jay

[OilDrum68]

NOS = New Old Stock

So it was an original part that happened to never have gotten used. Usually also highly desirable in an era where the knockoffs keep getting more cheaply made every year.

[chipflyer]

I had the same issue after buying a sender at Orelly auto. A week later I stopped at Classic parts in KC and picked up a new one from them and the needle is exactly where it should be now. Before I would change anything else I would get another new sender, I don't believe most of the cheap ones are calibrated correctly, I have seen this same issue from others here more than a few times.

Jeff

[VetteVet]

In order for the sender to work properly it has to have a good ground to the engine block and to the negative battery post The block is grounded if the starter works and the alternator charges OK. If you used any sealant on the new sender when you installed it then it may not be grounding as well as it should . this will result in higher temperature readings on the gauge.

[mightyatom]

I did not use any sealant but there was some teflon tape on it out of the box which I did not remove. Should the braided ground strap on the bulkhead behind the engine attach to the block or should it go somewhere else ?
Currently it is just tucked up behind some small tubes going down the bulkhead. Seems like I should fix this before anything else.
I have a 1972 shop manual on order but until it arrives I am a bit stuck on where the disconnected wires need to hook physically hook up to.

Thanks
Jay

[PowerPro]

Connect the ground wire to the closest available clean bolt on the block. (clean the area where it will contact the block first)

I'd suggest pulling the sender back out, removing the tape and re-installing. Usually they have a tapered thread that seals them plenty. If it leaks, find a liquid thread sealant designed for conductivity.

[mightyatom]

Well I feel a bit foolish as I think I took a step backwards yesterday. I connected the ground cable from the bulkhead to the block. I drained the radiator, removed the teflon tape from the temperature sender and replaced the thermostat (190 degrees). When I removed the thermostat housing which was a bit stuck the old thermostat fell out before I had a chance to see how it was installed. I took a look in the Haynes book and it was with the spring to the block so I installed it that way. I then parked the truck facing uphill and filled with water.
I went for a drive and the temperture went straight to the top of the gauge. I checked the radiator hoses and bottom one was very hot, top one was cold which suggests the thermostat is not opening.

1. Can someone confirm that I mounted the thermostat the correct way ?
2. If its right, why is it not working now - bad thermostat, water not up to temperature, other ?

Jay

[PowerPro]

Did you pull the radiator cap back off to check to make sure you re-filled the coolant after all the air-bubbles worked out? Those symptoms sound like a not completely filled coolant system.

BTW, yes, that sounds right for the thermostat install.

[67chevemall]

When it opens the gauge should stop moving up and even move down a little bit.
Get the colder one which means it opens up sooner.

I fought with my gauge for days but the oposite reason. It takes almost 30minutes for the gauge to move at all....I changed and tested parts till I gave up.....then sure enough when I went for a LONG crusie one day 30 minutes or so into it the gauge went up and I was like your kidding me!!! lol

[neba]

why not take the thermostat out and see what happens.my guage also shows hot when i know it isnt. im going to try another sending unit. you can also put thermostat in a pot of water on the stove. water boils at 212. you shoud see it open before that.
there is a small recess where theromostat(spring down) goes in. make sure you install thermo before gasket or it can get off-center. it can crack housing if this happens

[mightyatom]

Finally got it running yesterday with the temperature gauge in the middle. I ran the engine a while to get out any air bubbles, topped it up as it cooled but still had the issue with thermostat not opening. So I drained everything and removed the thermostat, stuck it in a pan with the original and boiled them up. Both opened about the same temperature (190 degrees). So I decided to take the new (190) thermostat back and exchange it for a lower temperature (160). I also picked up a new radiator cap while I was there as they are cheep.
I hooked it all back up again, running and filling and facing uphill on my drive. This time the water started circulating and temperature settled around mid-level on the gauge. I went for a 10 minute drive and temperature did not budge.
I know the 160 thermostat is too low and means my engine is probably not running very efficiently but at this stage I willing to put up with that until I drain the system again in the future. So my conclusions are:

1. Difficult to get air out the system -> Fill radiator and run a while, let it cool and top up. Parking on an uphill slope may also help.
2. 190 degree thermostat not opening -> may have been due to air in system. The original was the same and worked when I got the truck.
3. 160 degree thermostat working -> opening due to the lower temperature and water is circulating. May have done a better job at getting air out of the system. Downside is engine will run less efficiently.
4. Temperature sender -> still not sure on this. With 160 degree thermostat it pegs it in the middle of the gauge when water is flowing through the system. With the 190 degree thermostat, the water originally flowed before I removed the sender to get rid of the teflon tape. At this time the gauge needle was up to around 85% at normal running.

So I am thinking it is still really related to the sender. When I can I will try and get a new sender, preferably NOS and try it out with the 190 degree thermostat. But for now, at least I can move forward.

Many thanks to everyone who posted. Lots of great suggestions and a whole lot of help. Job 1 of 200 now 80% complete.

Jay

[neba]

just got a new sender and installed without tape.temp guage now reading about center of dial.

[mightyatom]

Arrrrggggghhhhh,
My overheating problem looks to have come back to haunt me. I changed the engine mounts over the weekend so took it for a run after and temperature gauge went straight to the top. It came down a little but stayed up around 90%.
When I had it running mid-gauge last week after changing the thermostat it did run high for a little while, at that time there was a slight grinding noise coming from the area of the water pump. After a while the sound went away which conincided with the temperature coming back down to mid-gauge. I may have an problem with the water pump which may not be pushing the water around correctly. I will change it out tonight and hope it fixes the issue.

Jay

[mightyatom]

<<< Neba >>>
Where did you get your new temperature sendor ?
Is it an NOS part ?

I still need to get a new sendor so as you have yours tried and tested I will try and get the same one. Let me know.

Jay

[mightyatom]

Yesterday I replaced the water pump and still had the same issue with water not moving around the cooling system as I guess the thermostat had not opened. I therefore decided to remove the thermostat completely and give it a run. This time the temperature gauge only went up 30% from bottom. I took the 160 degree thermostat and put it in hot water on the stove and it opened correctly. So I added it back in and same issue, temperature gauge went right to the top and water was not circulating.
So I can only reason that the reason the thermostat is not opening and allowing the water to circulate is that it is not getting to 160 degrees so engine is still cool, but sensor maxes out on the gauge. So it must be the sensor which I will now replace once I order a new one from a classic parts website.

I am beginning to dislike cooling systems, however basic. They don't play nice.

Jay

[mightyatom]

I got another temperature sensor from Kragen (WT203) to see if the first one was faulty but it has the same issue. I made sure there was no air in the system and the pointer goes off the end of the temperature gauge still. I was convinced it was not running hot so left it running a while and the thermostat does open and water circulates but the gauge does not budge.
I have therefore ordered an NOS temperature sender online which should arrive in a few days. If that does not work, not sure what to do next. I will update after it arrives.

[mightyatom]

I got the NOS temperature sender from American Classics. I took it for a 10 minute run on the backroads after instalation and it did not go above half way up the gauge so I thought it was the cause of my problems.
Over the weekend I had to take some concrete to the dump, was heading up the expressway and temperature kept going all the way to the top. I did see it drop a little but stayed b/w 80-95% . I checked and both upper/lower hoses were too hot to hold so coolant was going around the system.

So needless to say I am pretty stuck. I was thinking that backflushing the system may be a good thing to do so bought a kit. Currently the heater does not work in the truck and as the kit hooks up the heater hoses I was wondering if I can still do this if I do not have power to the heater?

Any help would be appreciated .

Summary of thing tried:
1. 3 temperature senders (2 Kragen and 1 NOS from American Classic)
2. new 160 degree thermostat and water pump

Jay