[Half-Inch Stud]

Crud for thought:

Just maybe, if there is 1-hot CYL, then there is an exhaust valve not opening enough, meaning bad cam lobe and loose Rocker arm if PolyLocks were used. Rocker may show tight for factory rocker nut and Lifters that were not pumped up when tightened.

[alanmay0]

I will take temp of spark plugs when I run it again. thanks

[alanmay0]

I think it just started after the rebuild. did drive it from florida to texas but the temp gauge was broke so not sure what temp it was running at. thanks. I have given all the info i can think of if you need more just ask me. thanks

[alanmay0]

here is a picture of the spark plugs on the drivers side that hat the 290 degree temp on center exhaust ports. also a short video of the water in the radiator as it is running. Let me know if the bubbles you see could be a bad head gasket. thanks. Is there a way to upload a very small mp4 file?

[Half-Inch Stud]

Originally Posted by alanmay0

I think it just started after the rebuild. did drive it from florida to texas but the temp gauge was broke so not sure what temp it was running at.......thanks

Surely you opened the Secondaries at some point, if it didn't ping hard from FL-to-TX then all is indeed well.

[alanmay0]

That was before the engine rebuild a few weeks ago

[alanmay0]

could these be considered the type of bubbles in the radiator that would indicate a bad gasket?? I have a short video but guess cant upload video on this site.

[alanmay0]

spark plugs from driver side

[Joe's Garage]

That way, when you run the engine, any air will bleed of fairly quickly.

There should not be ANY bubbles circulating in the system when the water is full and it is at operating temperature. None.

Any bubbles, particularly a steady stream of little tiny bubbles indicate a leaking gasket. Not blown, just leaking.

I think your spark plug for #5 looks a little too clean compared to the others. That would be where I would look first.

Good luck!

[alanmay0]

would this cause the engine temp to go up to and past 250 degrees

[prostreet64]

you bet, super heated exhaust gas will heat up the coolant very fast, of course depending on how compromised the gasket turns out to be.

[Joe's Garage]

We had a 'leaker' that would fluctuate between 230 and 250* steadily up and down. Never overheated, just ran hot and fluctuated.

And there was always a steady stream of tiny bubbles in the coolant.

Gasoline's ignition/burn temp is 495*, and the temp inside the combustion chamber, with the gases burning under pressure, is around 2800* and can approach 4000* under certain circumstances.

So, YES, even a small amount of combustion gas will heat the coolant up really quickly.

[LPete]

Originally Posted by alanmay0

Even with the radiator cap off and the engine running it still climbs up to 250 just idling. does not take more that 10 minutes once thermostat opens.

You can have the radiator cap off when the gauge says 250? The gauge is lying if that’s true.

[alanmay0]

OK maybe 225 heading to 250 but I turned it off.

[LPete]

Your gauge said 225, you shut the engine off, still with the radiator cap off, and it didn’t blow coolant all over? 50/50 antifreeze/water boils at about 223, and I’d think it would have instantly boiled over if it was really that hot.

If your elevation is higher the boiling point will be lower. At 5000 ft our boiling point is 10 degrees or so lower.

["QUICK-SILVER"]

Originally Posted by 25stevem

I would bet that the bank of the motor who’s center exh ports read 295 has the bad head gasket ,

I would have to compare end exhaust port temps on opposite head to rule out carb adjustment or a vacuum leak.

Clay

[John V.]

You mentioned you are running 60:40 coolant to water mix?

That will raise the boiling point but generally, I believe water may provide a bit better heat transfer. And if you haven't tested the mix, maybe you are running an even higher concentration?

I suspect a mechanical issue but just suggesting something else to consider. I realize you are in Texas and perhaps 60:40 is common there because of high ambient temps. Worth checking perhaps.

Next, you mentioned the intake crossover was blocked which is a common practice especially since our old Pontiacs mostly aren't driven in winter cold.

But a '67 would have used a RH exhaust manifold Heat Riser Valve. Just curious if yours was eliminated. With a blocked crossover, a stuck closed HRV would be a big issue but I'm thinking a stuck partially closed HRV couldn't be good for engine performance generally and probably cause high temps.

Hopefully yours has been removed or permanently opened.

You confirmed that you have the 8 bolt style Flowkooler water pump and you used the early style two divider plate package. As others have stated, the rubber seals were not used with the 8 bolt and assume the Flowkooler wouldn't need them either.

I think lots of folks have used a Flowkooler pump so I assume no issues there. For stock engines and radiators I have always been a proponent of stock pumps as they were designed for a specific flow rate to give the coolant residence time through the radiator. Pumping through the radiator too fast would not allow time for the best heat transfer.

When my engine was rebuilt, we used lifters I had purchased in the early '90s. One of them never pumped up. On disassembly it was discovered the lifter had come apart. IIRC, I was told lifters from that era had issues. The fresh engine had only been run for some minutes but we decided to replace the cam along with the lifters rather than worry about a wiped lobe. But seems to me you would know if you had a lifter/cam issue at start up well before it got hot.

Some years ago, I remember a guy was overheating. His upper rad hose was too long and trapped air (think an upside down drain trap effect). IIRC, he shortened the hose so that it wasn't arched above the inlet. That seemed to cure his overheating as the air was no longer trapped. Since you aren't boiling coolant, I would be suspicious of a temp misread because of air in the system but based on what you've done, aside from the hose configuration, I doubt air is your problem and the coolant really is getting that hot.

Since you saw a 53 deg F difference in center exhaust port temp from RH to LH head, I'm with 25stevem about the head gasket on the LH side and also Joe's Garage who judged the no. 5 plug looking a bit too clean vs. 1, 3 , and 7.

Your engine builder should be able to test for a head gasket leak. Since he re-ringed the pistons, did he install new head gaskets?

[68WarDog]

What's the overbore with your 670 heads? Have you noticed any sounds of detonation ? Would you be able to run some 110 octane fuel?

[alanmay0]

Thanks for all of your information. Yes new head gaskets were installed. Again today I rented the tester for telling if exhaust gases were in the radiator. I checked and double checked with this tester and could not get the blue solution to turn yellow. I did test the solution buy holding it by the exhaust pipe and it did turn yellow. Yes the heat riser is frozen in the open position. Today after adjusting the carb. the 53 degree difference between exhaust sides seems to have corrected itself and they both pretty much read the same. So today i also checked the compression and all cylinders were between 145 and 150. So you know I have an aluminum radiator and two 12" fans from Butler Performance who stated that this combination would cool any car on the road today. Not Mine. When the thermostat opens you can see the water flowing and the heater blows very very hot air. So the pump is working. Is it working too good maybe. I can tell you that the temp, when taken with the laser temp gauges, at the thermostat housing and again taken at the water pump intake where the lower radiator hose connects to the water pump are basically the same. The guy at Butler told me that a radiator can take about 30 degrees out of the water temp from top to bottom. This is not happening with my engine. The temps are about the same. Meaning that not much heat loss through the radiator. Both 12" fans are on but not pulling enough heat, or pulling all they can. Like i mentioned in my earlier post I have tried a different radiator and i have tried using the 7 blade clutch fan with no changes what so ever. So any suggestions you may have would be appreciated. I was thinking of tomorrow removing the plates under the intake manifold so that the exhaust could flow through the intake, dont know if that would make a difference. I am aware of what you are talking about with the large top radiator hose. I have seen those. Don't think mine is that long. I have been told that I might have a air pocket but I have changed the radiators and anti freeze so many times and flushed the system that I find it hard to believe that an air pocket is possible. I could be wrong. Any help appreciated. Thanks

[alanmay0]

The cylinders were bored 30 over on a previous engine rebuild. This rebuild cylinders only honed. No detonation at all. Don't know if I could run 110 fuel because in Texas you can't get it. Remember before the recent rebuild, 150 miles ago, I drove this car from Florida to Texas with no problems. although the temp sending was not working I detected no overheating problems at all. So something changed with the rebuild, I used the same water pump because it was a good one and worked fine. Very very confusing. I can not think of any thing else to try. So any help appreciated.