1972 chevy 1/2ton pickup overheating, not sure why?

[chevman51]

I just purchased my brothers 1972 chevy pickup that he was restoring. He put a brand new chevy 350 in it that's built pretty good with cam and so on. The pickup will overheat just sitting there idling in the driveway. I pulled the thermostat out and the gauge will stay down. I put a new thermostat in and the gauge just creeps back to the hot again. I looked at the water in the radiator with the truck running and it looks like its circulating so the water pump should be working, right? Where else do I go from here?

Thanks Tony

[cdowns]

have you taken the temp of the coolant with a know good thermometer??

old gauges aren't always a good read

you can get a cheap good thermometer in a grocery store

[Shyguy]

Does it have a fan clutch?

[cuda581]

Does it have a fan shroud?

[rsavage]

Is it a clean and and appropriately sized radiator that can handle a built motor? If just an original 2 core that is built up with decades of gunk, it won't work well. 4 core original type or a 3 core aluminum might be needed. Do you have a shroud? If not, you'll need one. If you have one, is your fan about 1/2 way inside at least? 160 degree stat will also help some. Are you running coolant? Do you have a good pressure cap 13-15lbs on a new radiator 7-9 on an older rad? Bottom line though, if you are sitting idling in your driveway for long periods of time in warmer weather, you are probably not moving enough coolant and air to keep it cool.

[Paul M]

also make sure the bottom hose isnt collapsing once it heats up. if it is need the spring in it to prevent that.

[chevman51]

no fan shroud or fan clutch. I will take the temp tonight and find out how hot its getting.

[GASoline71]

Prolly just an old radiator that needs to be either replaced or rodded out.

Is the T-stat installed upside down?

Gary

[LMN8UR]

It doesn't overheat without the thermostat? But with the thermostat installed it can't flow enough coolant.
So that tells me that the added restriction of an open thermostat causes it to overheat, which means the cooling system isn't flowing enough cooled coolant. (A. Water pump not pumping enough, B. Radiator to small or plugged, or C. Thermostat not properly installed)
How old is the radiator? Is it a 2,3, or 4 core. Rodding or flushing a 40 year old radiator will probably be a waste of time and or money.
If the radiator is a 2 core, replace it with a 3 or 4. (4 core requires different brackets!)
If you have access to an infrared thermometer check radiator for cool spots or signs that rows have been plugged.
Run some super flush through it (Don't be surprised if you open up some leaks!)
Get a high flow thermostat (Less restriction to coolant flow).
And if all else fails, Try some Water Wetter?

Good luck!

[joes50pu]

Is the carburetor adjusted so it's not running lean? Check your timing as well.

[mclairmo]

First, you really need a shroud to ensure all the air being pulled by the fan goes through the radiator core. Not only does the water pump need to circulate the water through the engine, you also need the radiator to efficiently transfer the heat out of that hot water. Also, use a hi-flow T-Stat and make sure it is opening at the correct temp by putting it in a pot of water on the stove. Use a meat thermometer to take the temp of the water. Also, make sure that your water pump pulley is noticeably smaller than your crank pulley. Otherwise, you will be spinning the water pump too slow and that could also cause a low speed/idle cooling issue. Make sure radiator is not clogged.

[dougminton]

You said it was a "new" 350 could it have a reverse rotation "new style" water pump that's being turned the wrong direction? Just something else to check.

[El Jay]

Are you getting an air lock in your water jacket when the thermostat's installed?

I always drill a couple holes in the T-stat flange to guarantee a water flow. (That's an old T-stat I had lying around)

[chevman51]

I checked the stat and it is a 180 degree. So should I get a high flow 160? The Cap is a 16lb, Should I also get a lower one? The radiator is a new 4 core, so that should eliminate that as a problem. How do you check the water pump to find out if it is turning in the wrong direction? I have never heard of that happening. When the truck is idling in the driveway and you pull the cap off you can see the water moving a little but when you rev it up it moves a lot more and you see bubbles. Is that normal? Thanks for everybody's advice.

[lovnthe70]

The air bubbles could be an indication of a head gasket leak, im in the middle of troubleshooting a similar problem myself, i just haven’t had time to do anything lately though. I would let the truck run for a while with the cap off so any excess air can get worked out of the system and then rent a pressure tester from autozone or somewhere and do a pressure test. I would also stick with the 180 t stat and get a new cap. good luck! and you also said you dont have a shroud? I would pick one up as they can make a big difference.

[bikertim]

Does it overheat when you drive it? That can tell alot --- if it only overheats when sitting at idle --- you really need a fan shroud and a good fan --- not one of those flexifans!

[chevman51]

I had started in the driveway and it was 40 degrees outside and the gauge was climbing. I drove it done the road and the gauge kept climbing so i shut the truck off and let it cool, turned around and went back home. Why would you stay with a 180 t stat? I'm getting a fan shroud but I have never had my other pickup without a shroud get this hot, so that makes me think there is more of a problem.

[joes50pu]

Bubbles in the water is a bad sign. Looks like you have a head gasket problem. To find out which cylinder is leaking into the water you pull the sparkplugs and apply air into the cylinder one at a time with tool designed to thread into the sparkplug and the other end hooks up to shop air. When you find the bad area, the bubbles will start appearing at the radiator cap area.

[lovnthe70]

If your gauge is climbing that quickly i doubt the shroud is your only culprit, i would still get one but it is not the only thing wrong. I would do like someone above posted and make sure your temp gauge is working (they have digital gauges you just point and click to verify the temp, check the temp in your block) if your gauge is wrong you might not have a problem at all. I would stick with the 180 t-stat because changing to a lower temp t-stat is not going to fix your problem and your engine needs to run at a higher temp to be efficient(you also live somewhere cold 40 deg!! ) I live in Arizona and we are at 105 some days and i still run a 180. Then cycle the air out of your system, get a new cap and a new t-stat and like the other guys said make sure it works before you put it in by testing it on your stove and drill holes in it. Then do a pressure test and verify that you are holding pressure.

[rsavage]

I would. Once you overheat a stat, it has been my experience that they no longer work as they should - it might be one of the reasons why with it out it doesn't overheat. If your radiator is new it should hold the pressure so I see no reason to get a lower pressure cap as that will only make it easier to boil. I would get a shroud, a new 160 stat, make sure the timing isn't too advanced, and not idle it in the driveway for long periods of time, as you are not going to move enough air to keep it cool.

[mrein3]

You're dealing with WAY too many variables here. This is what I would do in your situation.

#1 I'd get the proper shroud and a 7-blade factory fan and new fan clutch.
#2 I'd run a 192 degree thermostat.
#3 I'd change out that thermostat and burp the system. I would not start that engine again until I'm burping it with #1 and #2 complete.

To burp it fill the radiator to the brim, leave the cap off, put a catch pan under the cap area of the truck and start it. As the truck warms up you'll notice flow then no flow as cold antifreeze from the radiator is exchanged with hot from the engine. When you notice a good, constant flow, top it off and put the cap on.

The system is now burped - you removed all the air from the coolant system.

NOW if you overheat you need to worry because except for a new radiator, your truck is now functioning on the coolant front the way the General intended it to.

Let us know what it is doing after you get the right parts on there.

[mdwilf]

Lots of good input here. I would look down in the radiator, see if the ends of the cores are clean or crudy. If crudy, fill the rad with vinegar & let it set a few days.

Before I did too much work, I'd verify the gauge, sender & wire are good & that the gauge & sender are compatible. Shroud will make a huge difference, but I've run several without it.

When it starts showing hot, turn on your heat & see if it feels unusually hot. If you get caught out in an overheating vehicle, turn the heat on full blast, this may save your motor. You'd be surprised at how much you can cool a motor down this way.

Be wary of the cheap aftermarket temp gauges, I've had several that were inaccurate.

[mightyatom]

Did you replace the temperature sendor ? I had a similar issue after I replaced it with a new one from Kragen/O'reily's, the gauge kept saying it was overheating but it was not. Once I ordered an NOS temperature sendor from Classic Parts it fixed the issue. Below is the thread.

http://67-72chevytrucks.com/vboard/s...d.php?t=393670

Jay

[mclairmo]

Read the below that I found from Corvette Specialties of Maryland, Inc.

Can you repair my temperature gauge?

It reads high, but my 'Vette is not actually overheating.

COMMON CUSTOMER COMPLAINT: (Applies to all Corvette electrical temperature gauges from 1955 to approximately 1972.) Customer will usually add the following: I know it's not the sending unit. I've already replaced that.

REALITY: ALL, (I mean ALL), each and every new sending unit that is sold presently is wrong. I don't care what the parts guy tells you or what the parts manual says, they are wrong. There is an exception to this, which is to find a New Old Stock (NOS) part. To my knowledge, these parts have not been available for at least 20 years. Our testing of a known good original sending unit and the currently available part, shows that both units read nearly the same - until the water temperature reaches approximately 180 degrees. From that point and higher, the correct sending unit will maintain accuracy, but the replacement unit will give you a reading that is approximately 30 degrees higher than the actual temperature. Unfortunately, in our opinion, the addition of a resistor (to alter the reading of the replacement part) is inappropriate. The readings are not consistent throughout the normal temperature scale. They do not vary (enough to be a problem) until approximately 180 degrees. For those of you that have a car that rarely exceeds 180 degrees, you will not notice an inaccurate reading with the replacement sending unit.


SOLUTION: We currently have a GM licensed reproduction sending unit with correct calibration for $22.00 each. The appearance is like the original, including the wording "A.C.- Made in USA.-12 Volt". You may also replace the sending unit with an original type. It may sound difficult but through research, we have found that many GM products from the 50's and 60's used a sending unit that will work in your Corvette.

I also read another article that explains that the newer AC Delco G1852 water temp senders are the same as all the aftermarket one and are wrong. As such, if we are using these new aftermarket units, our guages will be wrong. I am going to buy the repro Corvetter one and see if that is accurate.

[GuyO]

Hi, I know this is an old thread but ... someone else may have what appears to be an unsolvable heating problem. I had something similar happen to me years ago and the normal fixes didn't work (e.g. radiator, thermostat, hoses, shroud, etc). What it turned out to be was a missing plate behind the water pump. When the water pump was replaced by a mechanic, the new pump didn't have the plate so the old one was discarded. Some 350's have a molded sheet steel plate that mounts to the block and the pump mounts to it. The plate helps the pump to build pressure and directs the coolant to circulate correctly.

It was very strange because some 350's had the plate, and apparently others did not because even the GMC dealer was in the dark. Once I found a plate at a junk yard and installed it, the problem was solved. Good luck! GuyO.