If you have a 3.90, 4.10 or 4.33:1 rear gear ratio, a Pontiac engine will overheat if you drive it on the street and there is nothing you can do about it. Especially if you have a 455 engine.

Those gear ratios are for “acceleration contests” only according to the Pontiac Zone Office Representative in charge of vehicle warranties. I had the same problem with a new 1969 Firebird 400 with a 4.33:1 Saf-T-Track.

 

Gee , that's funny , as the o.p. stated , it worked fine until the repair shop overheated it ....

 

This thing wont lie. You will let the car run until it warms up without the cap on it. Make sure your coolant level is low enough that it doesn't flow over. If its real bad you wont even need the tool, you will see bubbles before the car even warms up.
https://www.napaonline.com/en/p/BK_...BRBpEiwA31VZj0wXSsHDUw0wmPWjs9fJWY3HaGRTKimCZ7KA2DguzdsSB93XjsyNlRoCTWIQAvD_BwE

Oops just saw the last line...
Make sure you are using it correctly.

 

A cracked head, just by the fact it is cracked, won't make an engine run hot.

It has to be cracked to the point it is either leaking water or pushing combustion into the waterjacket to effect engine temperature.

Based off the fact the engine isn't eating water and appears to have no signs of combustion leaks that would eliminate a head crack being a problem.

Same info above would also apply to cracked block...if it isn't leaking water or combustion it isn't the issue.

I don't have another answer for you, but think you need to look elsewhere beside banking on a head being cracked.

Cooling at idle but not under load or out on the road at cruise speaks to either water flow rate/volume or system volume capacity insufficient.
The info that one side is 20° hotter also points to a pump/divider plate/flow type of issue.

I do however, agree with Excellenceautosoluti, you need to do a real combustion leak test to truly eliminate that possibility.

Insufficient ignition timing will drive temps up too.
Are you using a vacuum advance??

Any chance you've talked to a Pontiac specialist like Butler Performance??

 

To the o.p. could the heads or block be cracked .........Yep !

 

Overheating a Pontiac engine is not uncommon due the faster piston speed which is a result of the longer stroke. Cooling Pontiac racing engines has always been a problem and can be made worse by other problems such as timing, radiator air flow, under hood baffling, etc.

Starting in the late 1960s, raising the back of the hood three inches was a way to increase air flow through the radiator.

If everything else is the same, and as a result of slower piston speed, a Chevrolet 350 will run cooler than a Pontiac 350 at the same RPM.

 

Theres a 73-4 400 block in my garage I can take pictures of. I drove it about 80,000 miles. It was an old rebuild when I got it.

It had been bored .060. Was always tough to keep cool. Started pushing coolant out two states from home but I limped it back at night. Three holes on the right bank had obviously started to wear through on the thrust side of the bores. Patches of porosity are visible.

When I had my first 400, a '75, rebuilt, I had them stop boring at .040 and sleeve the worst hole.

I have had a 72 big car 455 in my 69 GP for 11 years and it was built (.030 over) about 15 years prior to that. I just drove it twenty miles across town in 90°+ heat with an original clutch fan setup and brass / copper 4 row radiator. Might have got up to 205.

Never entered the aluminum world, never was a mechanic, and even now I am just a bodyman. Who drives only Pontiacs. All that to say that my questions to the OP are...

How much has the block been bored? Any sleeves? Early or late casting? I don't know where to point you but this iron head era dude says hey... careful with them Pontiac blocks. They can be mighty fragile at this point in time.

 

Thanks for all the quick feedback. I tried to do a leak detection/block test but the bulb had a really hard time pulling anything though it. When I thought that maybe the bulb was just really cheap and couldn't create enough suction I rigged up a hand pump to draw air through it. Eventually it just started pulling coolant into the test and I had to redo it. I thought I had the coolant level low enough to perform the test. It's worth another try I guess.

Think I have the gears at 3.42:1. I forgot to say that it does have an aggressive cam. But again I had it running cool prior to it sitting for a few months and then making all of the coolant system upgrades. I kept thinking eventually I'd find the problem and with all the upgrades overheating would never be a concern again.

I've run two hoods on this car. One with a cowl and now with a hood scoop that I made. It also has no inner fenders in the front so I feel like it gets plenty of air.

Recently I have been throwing belts and seeing lots of belt dust. It looks like all the pulleys are in line and I have the proper spacers for the power steering pump. There's a very slight shifting motion (forward and back) to the power steering pump pulley.

I don't know if the block has been bored out at all. I haven't done anything to it. I added a windage tray when I had the engine out since that was missing. Really thought I found my issue when I found the crap in the motor when I pulled the freeze plugs but still gets hot.

Could there be an issue with the Mallory distributor? It has an electric module in it instead of weights and springs.

 

Hello,
Welcome aboard...
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Friend of mine back in the day had a '68 GTO 400" 4 speed with the then popular 4.33 rear... it never overheated and was his daily driver... it did always seem like it needed one more gear to shift up into, though... LOL!

Did you use a High Flow thermostat?

Did you do a compression check on all 8 cylinders looking for warped/overheated valves?

Overheating may have damaged an EFI sensor or injector and causing a lean or rich condition, do you have an Air Fuel ratio A/F meter?

Could there be an issue with the Mallory distributor? It has an electric module in it instead of weights and springs.

Does the timing look like it's doing what it should be doing when watching it with a timing light?
.

 

Yes...vacuum advance on the distributor.

 

I believe I have a high flow thermostat laying around that I tried once. I have a standard 180 thermostat in there right now. I'll find it and put it back in. I have a brand new AutoMeter gauge that I trust more than the Fitech reading. They each have their own sensor on either side of the thermostat housing. The Fitect reads lower than the AutoMeter gauge which goes along with what I'm reading on the IR gun. Autometer sensor is on the driver side showing it's hotter and the Fitech sensor is on the passenger side showing it's a little cooler.

The radiator hose gets pretty close to the top of the top of the AutoMeter sensor. I doubt that would have that big of an effect though. The hose runs out of the thermostat housing at a 45 degree angle instead of up and over like it was originally designed to do. It's the same hose that was on it when I bought the car 7 years ago. I replaced the thermostat housing only to find out the hose should be going up and over instead of out at an angle. Guess the previous owner cut the turn down on the hose off and had it run out at an angle. But I keep coming back to the fact that regardless of that it was running cool. I tested the mechanical gauge that was in there before I replaced it to see if it was accurate and it seemed to be pretty accurate.

 

I'm located in Bluffton, SC. That's on the coast near Savannah, GA or Hilton Head Island, SC.

I have not done a compression check on the cylinders.

The EFI is basically an electronically controlled carb and I added it after the overheating issues started. There were some missing linkages on the Edelbrock and a buddy talked me into getting the Fitech system.

I'm pretty sure the Fitech will give the Air/Fuel ratio. It has a little handheld display that gives that information.

Yeah the timing acts normally when I'm checking it with the timing light. I didn't use the vacuum gauge when I set the timing. Have one just didn't use it. Really just went with sound.

 

I was stationed at Hunter Army Airfield in Savannah in 1970 while in the Army... it really does rain every night in Georgia... LOL!

Ignition timing looks weird with the vacuum advance connected, did you time it with the vacuum advance disconnected? Does it connect to the EFI throttle body or to the intake manifold?

An oil cooler may help... if oil gets too hot, then the coolant also starts overheating...
.

 

If you happen to have a laser IR temperature gun, shoot the radiator tank right next to the inlet and outlet.
Do it at idle after it warms up, maybe again after it has idled for a20 minutes and starts to get hot like you've mentioned, and if you can drive it until it gets hotter than you like and check it again....see what the temp drop across the radiator core is.
This might give you some clues.

 

So I just scrolled through the whole thread. And maybe I just missed it. What temperature are you running, that seems too hot? Some guys don't like 2:10 or 2:15, but sometimes they run good at that temperature. It's when you start getting up there past that is when you have to worry...

 

BuzzLOL Yeah lots of rain especially during the warmer months. Its raining now actually haha. I did set the timing with the vacuum advance disconnected. I plugged the vacuum line coming from the EFI throttle body when I did it. I'll look into the oil coolers but was hoping it would be something I didn't have to throw more parts at.

ericnova72 I haven't gone that route yet. I've used the IR gun to look for dead spots in the radiator but haven't monitored the inlet and outlet temps at different stages yet. That's a good idea.

Excellanceautosoluti I've been cutting the car off when it gets to 210-215. I guess I thought with everything that I've done that I could keep the temp down more than that. Anything higher, like you said, gets me worried. I assumed it would keep going up if I didn't cut it off.

This weekend I have a few things I can try then. I'll put that high flow thermostat back in. I'll check the timing again and use the vacuum gauge. I'll try the block tester again, maybe dropping the coolant level more when I try it. I may also pull the water pump off and make sure I don't have something blocked off that I shouldn't have. I'll try and get my hands on a compression tester too and test the cylinders.

 

I'll look into the oil coolers but was hoping it would be something I didn't have to throw more parts at.

Excellanceautosoluti I've been cutting the car off when it gets to 210-215. I guess I thought with everything that I've done that I could keep the temp down more than that. Anything higher, like you said, gets me worried. I assumed it would keep going up if I didn't cut it off.

I may also pull the water pump off and make sure I don't have something blocked off that I shouldn't have.

I'll try and get my hands on a compression tester too and test the cylinders.

There are thermostatically controlled oil coolers that divert the oil flow to cooler or not depending on oil temp... if all else fails...

https://www.hotrod.com/articles/engine-oil-temperature

As Excellence says, we usually don't get too excited if it never actually boils over...

Don't think Pontiac engines were around long enough to get into reverse rotation water pumps for serpentine belt systems, so that shouldn't be a problem... unless the aftermarket created some...

Compression testing can discover or rule out a world of problems...
.

 

You say you had it running at 195 degrees back a few months ago.Is the ambient temperature (outdoor temperature ) the same now as it was then.

215 degrees is not overheating 240 is getting hot and leaning on scary.

Have you checked to see just how hot it will get? Like has it gotten to 225-230?

Why not carefully see what temp it will run at , or see how long it rubs before it gets kinda scary like 230 ish. Maybe it will max out at 220?
Just a thought.
About all I can think of is the water pump impeller may have come loose (stamped steel) .

Also, I know you have a 68.Is it an 8 bolt water pump or 11 bolt?

 

About all I can think of is the water pump impeller may have come loose (stamped steel)

Maybe check the amount of clearance between the water pump impeller and the rear housing... make sure it's the correct impeller...

 

I'm kinda wondering if like the parking lot attendents in Farris Bueller's Day Off if the jockies at the shop took it for a joy ride and did more than forget to turn the cooling fans on.

Bogie

 

One of the things a compression check would prolly reveal...

 

The 1973 and later Pontiac blocks are thin wall castings compared to 1955-1972 blocks.
They will run hotter than normal with a .030” over size bore and those blocks should not be bored .060” oversize.

You should use a pre-1973 block for boring oversize, if you can find a good one. They are getting scarce today.

 

The Pontiac block to use is a 1964-1972 block. The 1963 and earlier blocks have starter and flywheel gear issues to overcome.

 

Thanks for all the input. Life happened this weekend and I had to take care of some other things before I could turn my attention to the car. My plan is to work on it today and try/check on some of the things that were suggested.

I haven't noticed a drop in coolant. I've pressurized the cooling system before but haven't left it pressurized for more than an hour. I plan on checking the timing again. Then I plan on pulling the water pump to check the impeller and bushings. I'll spend a little more time monitoring the heat with the IR temp gun when I'm checking everything out. I don't think it's the temp gauge since it's new but if I'm still getting a high number on the temp gauge I'll switch sides of the thermostat housing with the two temp sensors to see how they change. Again I was getting a lower number from the passenger side with the Fitech sensor.

Could an old set of worn out headers add heat to the heads? When I put the motor back in I used the thin header gaskets that came with the gasket set. I have some leaks around the header to head connection and I've welded up several pin holes in the headers as well. They were wrapped when I first had the car but I can't tell you exactly when I cut that stuff off (years ago). I've noticed some discoloration in the fresh paint on the heads but I thought that'd be the only problem I would have because of the leaks until I got new gaskets. Again, I don't have inner fenders so I feel like air moves pretty freely through there.

Appreciate all the help. I'll keep you updated.

 

Could an old set of worn out headers add heat to the heads?

Actually, headers help remove heat from the engine/heads... if there's a free flowing exhaust system behind them...

 

Just a thought, I see you have your antifreeze/coolant at an 80:20 mix. That’s not typically a mix to be used in warmer climates. It is a ratio that’s used in colder climates as it can take your coolant freezing levels to -70F or so but doesn’t do a lot for cooling. Before I started doing all the high priced things I’d go buy some new antifreeze, drain the system and start over whit new coolant mixed at a 50:50 mix. Let it circulate really good then top off as necessary to assure you have all the air out of the system. While you’re at the auto parts store buy a coolant test gauge ($10 or less) to help you check for the right ratio.

 

I did not see the 80/20 mentioned. Good lookin out .

Gawd Im a getting old. LOL

 

crackedheads

it is easy to check with a block test kit. you can probably get it at a parts store. Basically you are checking for combustion chamber gasses in the cooling system. Another telltale sign is a white cream in your valve covers or in the bottom of the oil fill cap.

 

Coolant mix

Here is Queensland Australia, I get my customers to use only Anti Corrosion mix ,not Anti Freeze. Cars will run a lot hotter with too much anti freeze and in your area I would also suggest using a Anti Corrosion fluid too. A lot of the stuff i work on are older Mercedes and the factory recommendations for coolant ratios are really for Cold Snow bound Europe,Not sub tropical Australia.
If you can,try another radiator Cap. If the cap is at all faulty(CCP made stuff really is crap) the pressure in the system is too low and the temp will rise accordingly ,especially under any sort of load.

 

If you're running an automatic transmission have you considered the possibility that as the tranny fluid heats up it rises your engine temperature? You mentioned that you installed a new radiator and fans but how about a transmission cooler ?

 

Distributor was my problem. I ran across a thread on here and Progression Ignition was mentioned. LOVE IT! You make the timing curve w/ your phone, easily. Don’t know if helps but helped me. Good luck

 

That was my question also. Years ago we had 400 4bbl TH400 in Pontiac Lemans. They had big radiators AND a added transmission cooler. They also had ps coolers. They generally only ran hot when idling with high electrical loads for a half hour or more. Sometimes though there was an impressive geyser, usually from a hose bulge and blow. His heat zone gets humid, so probably just plain water with anticorrosive and pump lubricants added. Maybe hook up a windshield washer pump to a spray bar in front of the radiator. Something like a derale thermostat controlled oil cooler? Maybe he had one and I missed it...Power/reverse flush the block? Pull and have the block boiled to remove flakes and deposits? I haven't read the thread all the way through yet. Thermostat gasket maybe blocking some flow? One side running hotter still nags me. I know two things for sure: I'd make sure at least one electric fan is thermostat controlled...second that the shop pays its share.