Looks like they’ve already confirmed the temp via two different senders, and are on the second radiator with electric fans
@ZooMad75 are the heads on this 327 heads, or from something else?
CK5
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Old School 327 running hot
- Thread starter ZooMad75
- Start date
@ZooMad75 are the heads on this 327 heads, or from something else?
From my experience the cold case fans are not even close to what they are rated for airflow. The one time I used their fans I had to replace them, I kept the shroud and radiator, those seemed like decent pieces.
Go back to basics, is the radiator hot or just the engine? If you have a 30 degree temperature drop through the radiator and the engine is overheating I would suspect waterflow. But if you only have a small temp drop through the radiator and everything is overheating I would suspect airflow. Obviously they are exceptions to this but it helps point to what to look at first.
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It’s got a single triangle casting mark on the end of the head I can see. If my google-fu is accurate it comes back to a ‘69-70 300hp 350 head though I did not confirm if it has a 041 casting number.
One more reason for the temp gun.
We can see good flow with the cap off the radiator. But without knowing temp differences it’s just what we can see.
, I’m in for the temp gun results. Also a plus 1 for a good water pump, went to a high flow Proform unit a few years ago and although it never overheated prior it’s not heat soaking as much, evidence by higher oil pressure at warm idle (same weight oil etc, no oil temp gauge to confirm), coolant temp is mechanical in the driver side of the block. The thermostat(195F) cycle shows on the gauge on even the warmest days. The 160F might not be allowing enough dwell time in the radiator?
You’re probably thinking about my thread with the overheating issues on my 97 BBC suburban. Ended up being a faulty water pump (new) that would cause it to overheat at idle.
Yep, I just wasn't positive if it was you.
Hey @ZooMad75 !! Any results yet??
We all be anxious to hear what you are finding!
We need and emoji that's eating donuts instead of popcorn to use in the mornings.
I was thinking a similar thought yesterday, how could it overheat just by making the iron cylinder thinner? The cooling passages have not changed. The only potential answer I could think of is if the cylinder was so thin it flexed and produced a lot of blowby, which could let a lot of heat into the oil and crankcase and not out the exhaust pipe. Now is .015" more per side enough to flip this switch?....seems doubtful, but plausible I guess.
I agree he likely has something else going on, weak cooling fans or faulty water pump or both combined.
I just reread @ZooMad75 original post, about the one side being hotter than the other, if this is true, I would change the water pump and/or do a compression and leak down to rule out some machining/mechanical assembly error if I didn't build it myself. I really like the Edelbrock water pumps because they are aluminum and made in the USA. Or stewart warner for iron pumps. I've had cheap pumps go out on me pretty fast, I stopped using cheap parts store pumps 15 or 20 years ago. If it's a stock driver I'll get a GM or Delco premium line pump. Pumping water with the cap open is a little easier than pumping water when the whole system is pressurized, not much, because it only needs a differential pressure, but still.
Another thing, how are the cooling fans wired? Its critical the fan (or each fan) has a good relay and a solid power and ground in at least 10 or 12 awg depending on the current draw of the fan. And if it has a weak circuit breaker or weak relay are you sure its not shutting back off after it has ran for a bit? Then resetting? Is the fan still running when the engine is hot in traffic? You should be able to use the fan wire from the EFI to trigger the relay, its more reliable than the little pieces you stick in the fins, I don't trust those. I use a a thread in thermal switch in the head or intake if I don't have EFI to turn it on.
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Didn’t bring the temp gun until today. So we’ll run it today and find out.
Here’s my thought on having a thinner cylinder wall. Mind you this is rooted in the idea that big overbores on a 327 is not recommended by the old farts I’ve known all my life. If the cylinder walls are thinner, the block isn’t holding onto as much of the heat and because of that the water/coolant is getting more heat pushed into it sooner and allowing the temp to rise.
Case in point this thing gets up to operating temp on the gauge in 5 minutes. Thats going from a dead cold start to hot at the upper hose and at or near thermostat temp in five minutes. Seems a little unnatural to us.
I spoke to the owner again yesterday and he still hasn’t got any call back from the engine builder. I guess the shop that built the car and the engine guy got sideways during the build and the engine guy is still holding a grudge or something. We may not get a true answer on the bore spec at all.
I am interested to monitor temps as it warms up at different spots on the block per side and the inlet and outlet of the radiator. I’m curious to shoot at the individual exhaust ports to see if the temps across from port to port line up or we have any significant outliers high or low to give an indication of how the fuel trim is.
Here’s my thought on having a thinner cylinder wall. Mind you this is rooted in the idea that big overbores on a 327 is not recommended by the old farts I’ve known all my life. If the cylinder walls are thinner, the block isn’t holding onto as much of the heat and because of that the water/coolant is getting more heat pushed into it sooner and allowing the temp to rise.
Case in point this thing gets up to operating temp on the gauge in 5 minutes. Thats going from a dead cold start to hot at the upper hose and at or near thermostat temp in five minutes. Seems a little unnatural to us.
I spoke to the owner again yesterday and he still hasn’t got any call back from the engine builder. I guess the shop that built the car and the engine guy got sideways during the build and the engine guy is still holding a grudge or something. We may not get a true answer on the bore spec at all.
I am interested to monitor temps as it warms up at different spots on the block per side and the inlet and outlet of the radiator. I’m curious to shoot at the individual exhaust ports to see if the temps across from port to port line up or we have any significant outliers high or low to give an indication of how the fuel trim is.
I've heard it mentioned many times through the years that boring an engine will cause it to overheat. Its always a conversation between a bunch of old guys drinking coffee....It does seem odd thought, unless less iron to absorb the heat before the water absorbs it? Agree though if .015" is making or breaking you, you might have bigger issues.
I still think it’s the pump
That said, the nerd-do-math part of me sees the overbore as an algebraic function in a scientific experiment. The removal of material does in fact change the thermal coefficient. We don’t know at what point we are on that function as to determine exactly how much .015” relates to that change
That said, the nerd-do-math part of me sees the overbore as an algebraic function in a scientific experiment. The removal of material does in fact change the thermal coefficient. We don’t know at what point we are on that function as to determine exactly how much .015” relates to that change
Honestly I hope it’s the pump. It would make things easy without major tear down. I’m not up for the math problem though. I’m sure there is something to it though. My thought is more material acts as a buffer to heat transfer. As it takes longer to heat up a thicker material before heat is transferred to the opposite side of the material and into the coolant. Thinner then would take less time as it heats up quicker.
I checked and the accessory drive system is from CVF and uses a standard rotation long water pump which we can get from anywhere. So if we need to get one we don’t have to get it from CVF.
The block will definitely have less thermal load capacity to store heat, simply because it has less mass or iron. However, the amount of material removed vs the total mass of the block seems like a very small percentage.
The thermal conductivity of the iron did not change at 200 degrees, that number can drop with with increased temperature of the iron, but that is minimal within the engine operating temperature. So it can only carry the heat away so fast no matter what.
The heat transfer coefficient of the coolant did not change with the overbore.
The surface area and finish of the coolant passages did not change where the coolant contacts the block during the overbore.
Now, perhaps if you go more localized, it is plausible that if the cylinder wall is so thin, the iron can't transfer the heat to the coolant or thicker parts of the block fast enough to keep that small portion of the cylinder cool enough to not boil the coolant, then you would have issues. But how thin is too thin, seems like .015" per side is minimal unless some of these older blocks had very thin cylinder walls.
I agree, I think its the water pump 1st since 1 side is hotter than the other, then the cooling fans, or both.
There also could be a mechanical issue with the engine.
Sounds like you already checked the timing. Engines run a lot cooler at idle if the vacuum advance can is connected to full manifold vacuum, not ported. If EFI is controlling the timing then this is done in the timing MAP, but many EFI base tunes don't have this in the idle timing, the tuner has to do it. I think this goes back to the old myth that you have to hook up the vacuum can to ported vacuum which was strictly for emissions and made the engine burn hotter at idle.
The thermal conductivity of the iron did not change at 200 degrees, that number can drop with with increased temperature of the iron, but that is minimal within the engine operating temperature. So it can only carry the heat away so fast no matter what.
The heat transfer coefficient of the coolant did not change with the overbore.
The surface area and finish of the coolant passages did not change where the coolant contacts the block during the overbore.
Now, perhaps if you go more localized, it is plausible that if the cylinder wall is so thin, the iron can't transfer the heat to the coolant or thicker parts of the block fast enough to keep that small portion of the cylinder cool enough to not boil the coolant, then you would have issues. But how thin is too thin, seems like .015" per side is minimal unless some of these older blocks had very thin cylinder walls.
I agree, I think its the water pump 1st since 1 side is hotter than the other, then the cooling fans, or both.
There also could be a mechanical issue with the engine.
Sounds like you already checked the timing. Engines run a lot cooler at idle if the vacuum advance can is connected to full manifold vacuum, not ported. If EFI is controlling the timing then this is done in the timing MAP, but many EFI base tunes don't have this in the idle timing, the tuner has to do it. I think this goes back to the old myth that you have to hook up the vacuum can to ported vacuum which was strictly for emissions and made the engine burn hotter at idle.
If that were to be the case, a higher flow water pump to carry heat away faster, or a higher pressure radiator cap could both help the situation. If the cap vents at too low of pressure, then the water boils at a lower temp and then you immediately have a problem. At 20 psig the boiling point of water is up to almost 260 degrees. But at 0 psig it's only 212 of course, so you can interpolate what happens if the cap is opening at only 5 or 8 psi or something. So the cap is another thing to try if you haven't.
If the engine doesn't start to boil over then the cap is likely not the cause.
If the engine doesn't start to boil over then the cap is likely not the cause.
Here’s another thought as part of your scientific experiment that has to be accepted:
When a 327 block is bored out, all other changes that are made to that rebuilt engine would have to be eliminated as a cause for the overheating: changing compression, changing cam, changing timing, any changes in friction coefficient. This also would imply that in factory bore configuration, these engines are borderline overheating. therein allowing the overbore to create the thermal problem.
When a 327 block is bored out, all other changes that are made to that rebuilt engine would have to be eliminated as a cause for the overheating: changing compression, changing cam, changing timing, any changes in friction coefficient. This also would imply that in factory bore configuration, these engines are borderline overheating. therein allowing the overbore to create the thermal problem.
Good points. We know nothing of the actual compression ratio, cam specs or if it’s installed “dot to dot” advanced or retarded. We can feel the engine has a little lope but nothing huge or causing low vacuum at idle. I’m guessing CR is reasonable because he didn’t mention having to run 100+ octane fuel. He might run 91 octane but it sounds tame enough to run our normal 85 or 87 octane swill we get in Colorado.
We also don’t know if the block or heads got a shave to clean up.
I recall cars seemed to always have more problem with overheating than the trucks. The space available for radiator and fan is I'm sure where that problem is rooted.
While the potential difference in head temp seems odd, overheating in traffic screams fans to me. The aftermarket fans, in the past anyway, were never enough. The ratings always seem faked, and cars predominantly seemed to have problems with overheating when aftermarket fans were used.
I don't see why one head running hot would make the whole engine overheat. The engine doesn't rely on the heads to shed heat. The heat input to the cooling system remains the same. Localized boiling can increase metal temps, so it's possible that's what is being seen. Not sure how, since that would require flow issues to that specific head, but who knows.
I'm not a fan of lower temp thermostats as a band aid for bad cooling. ALL it does is allow a larger margin (vs 195*) before the engine overheats. Thermostat governs the maximum engine temp. If it overheats with 195*, it will overheat no matter what lower temp thermostat is run, it will just take that much longer to overheat. Unless it's a very brief period that the extra ~30* of capacity would mask, applicability is minimal.
There is no such thing as moving coolant too fast, unless the pump cavitates or you somehow disrupt intended flow patterns within the block. A colder fluid ALWAYS absorbs more heat in the same amount of time vs. a higher fluid temp. Slow moving coolant (and low pressure) will exhibit localized boiling and will thus increase cylinder temps. The radiators ability to shed heat doesn't change, but moving coolant through it faster is akin to using a larger radiator as you are exposing more coolant to the same surface area in the same amount of time.
Even some cooling system component manufacturers can't get theory right.
While the potential difference in head temp seems odd, overheating in traffic screams fans to me. The aftermarket fans, in the past anyway, were never enough. The ratings always seem faked, and cars predominantly seemed to have problems with overheating when aftermarket fans were used.
I don't see why one head running hot would make the whole engine overheat. The engine doesn't rely on the heads to shed heat. The heat input to the cooling system remains the same. Localized boiling can increase metal temps, so it's possible that's what is being seen. Not sure how, since that would require flow issues to that specific head, but who knows.
I'm not a fan of lower temp thermostats as a band aid for bad cooling. ALL it does is allow a larger margin (vs 195*) before the engine overheats. Thermostat governs the maximum engine temp. If it overheats with 195*, it will overheat no matter what lower temp thermostat is run, it will just take that much longer to overheat. Unless it's a very brief period that the extra ~30* of capacity would mask, applicability is minimal.
There is no such thing as moving coolant too fast, unless the pump cavitates or you somehow disrupt intended flow patterns within the block. A colder fluid ALWAYS absorbs more heat in the same amount of time vs. a higher fluid temp. Slow moving coolant (and low pressure) will exhibit localized boiling and will thus increase cylinder temps. The radiators ability to shed heat doesn't change, but moving coolant through it faster is akin to using a larger radiator as you are exposing more coolant to the same surface area in the same amount of time.
Even some cooling system component manufacturers can't get theory right.
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I agree, the only caveat I'll add is the thermostat doesn't open instantly at it's setting, it opens completely over a range of temperature. So at 200 degrees a 180 thermostat should be open more than a 195 would be, this is one of the reasons why engines frequently run 10 - 30 degrees warmer than the thermostat setting.
I typically run 195 only in stock engines that had it from the factory.
I run 180 in my toys that have a heater for winter.
I run 160 (or no thermostat) in my toys for summer only.
The engine doesn't need to have any coolant restrictions more than necessary, we aren't trying to win a cup race or pass government regulations for the life of the vehicle. And for straight line performance without constant high speed airflow, you want hot oil and cool coolant, not hot everything so the fuel and air ends up hotter too before it finally gets burned.
For water pump vs fans causing the issue, I'll refer back to the differential temp in the engine block vs the radiator.
I am not a fan of the weak cold case fans, however, I don't see weak fans allowing part of the engine to get hotter than the rest, I feel like that points more toward a low water flow issue not evening it out. Or a mechanical or tuning issue causing that side to run hotter.
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