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I'm about out of ideas for things that can cause this overheating issue. I know the motor is still tight from the rebuild. New radiator, thermostat, 7 bladed fan, clutch. Shroud is new too. No - i dont have all the
seals on it but I dont think they really contribute much sitting still in my driveway. Sealing up between the radiator and shroud as well as fan placement in the shroud seems to be more critical to me.
Heck - i read some back posts here that 350 cars didn't even have shrouds from the factory.
Yeah my 70 cooled fine with no shroud, 4 blade fan and a 2 core copper brass rad. That is why I asked about the pistons. Someone could have used the Speedpro forged pistons and didn't add extra clearance.
Have you tried applying manifold vacuum to the distributor?
Yes - tried that. I didn't help.
We tried to richen up the fuel mix a little but didn't help. No vacuum leaks - everything was checked and rechecked. Timing also.
New aluminum radiator, high flow water pump, high flow thermostat, new 7 blade fan (18"). Nothing will make this engine run cool at idle. It is better than before though. It used to take 10 mins to overheat, but now its about 20-25. I'm wondering if all the extra cooling stuff is masking some problem that we just don't know what it is. Its only about 50-60 miles after a rebuild so it could be just that its tight.
Compression is about 130-135 psi on all cylinders. Pistons are .030 over. Not sure what cam it has - paper work was lost. Was told it was a mild upgrade when it
was rebuilt. I didn't do it. Engine really runs nice.
With all plugs removed, it takes about 35 ft-lbs to rotate crank. Might be on the higher side, but doesn't seem unreasonable. Can any of you Olds
experts think of anything else in that engine that could be causing this hot idle?
As soon as the car gets on the road, temps go right back down to 180. No issues there. Still scratching my head.
Yeah my 70 cooled fine with no shroud, 4 blade fan and a 2 core copper brass rad. That is why I asked about the pistons. Someone could have used the Speedpro forged pistons and didn't add extra clearance.
Is there a way to identify these possibly with a bore gage? We did put a bore gage in the spark plug hole and verify that they're 030 over.
Would this cause an issue only at idle - or all the time?
Last edited by Sierra442; Feb 27, 2024 at 05:23 PM.
100% the problem is airflow. Think about this intuitively. You've proven the radiator is more than capable of rejecting enough heat at speed, where's there is plenty of airflow and the engine is creating substantially more heat than it does at idle. You mention the seals around the radiator are not in place but you "feel" like they are not needed. Please consider whether your "feel" for what's needed is more accurate than what the Oldsmobile engineers decided was needed in 1970? Do you think they incurred the additional manufacturing cost associated with these seals if they were not necessary? You, giving it 10 minute consideration, know better than say 3-5 engineers working full time on the cooling system for maybe 1-2 years? Without the seals, the fan will suck some % of air AROUND the radiator instead of through it. If it takes 10-20 minutes to overheat, this difference in airflow could easily be the difference in heat dissipation you need to stay at a stable temp.
You should also verify the heat rejection capacity of your new radiator is more than what your stock radiator would have been new. Its not just about aluminum versus brass (fins per inch, # of rows, tank versus core size, etc). Usually with stubborn problems like this - its because of some previous assumption that was made that was incorrect.
Last edited by getmygoat; Feb 27, 2024 at 08:16 PM.
Yeah my 70 cooled fine with no shroud, 4 blade fan and a 2 core copper brass rad. That is why I asked about the pistons. Someone could have used the Speedpro forged pistons and didn't add extra clearance.
That's an interesting possibility. I don't think its the forged pistons that have the problem - but the hypereutectic? (The top ring land is thin so it positions the top ring closer to the combustion and less shielded from its heat). I had a motor built wrong with those pistons. The real threat is you can get a piston to seize in the bore and it blows the top of the piston off. Bye bye motor. Luckily in my case I reviewed the spec sheet and was like WTF?
100% the problem is airflow. Think about this intuitively. You've proven the radiator is more than capable of rejecting enough heat at speed, where's there is plenty of airflow and the engine is creating substantially more heat than it does at idle. You mention the seals around the radiator are not in place but you "feel" like they are not needed. Please consider whether your "feel" for what's needed is more accurate than what the Oldsmobile engineers decided was needed in 1970? Do you think they incurred the additional manufacturing cost associated with these seals if they were not necessary? You, giving it 10 minute consideration, know better than say 3-5 engineers working full time on the cooling system for maybe 1-2 years? Without the seals, the fan will suck some % of air AROUND the radiator instead of through it. If it takes 10-20 minutes to overheat, this difference in airflow could easily be the difference in heat dissipation you need to stay at a stable temp.
You should also verify the heat rejection capacity of your new radiator is more than what your stock radiator would have been new. Its not just about aluminum versus brass (fins per inch, # of rows, tank versus core size, etc). Usually with stubborn problems like this - its because of some previous assumption that was made that was incorrect.
I've given this problem about 6 months of consideration. I am an engineer yes, but not an automotive engineer. I appreciate your comments and I do have those front radiator seals on order.
I plugged up those holes temporarily and it did nothing. In looking closely, those seals close off the incoming air as they are in front of the radiator. I could see this having an effect while driving, but
sitting still just idling, they don't do anything really for making the air go thru the radiator. I do have the side rubber seals installed and everything needed to seal off the air on the shroud side of the radiator, essentially making sure that the fan is pulling air thru the radiator. I agree that all the leak paths around the shroud and radiator need to be sealed.
Also, i have read comments (above) some saying this car should be fine with an old 4 blade fan and no shroud. This is why I ask.
Was there an air dam along the bottom of the rad from factory that is present? I know air can be sucked from below also - and those lower dams can make a difference.
This is a little bit of a long shot - but those side openings could cause the fan to suck hot air from behind the radiator back through the radiator instead of forcing the air to come through the grills. Also - the partial vacuum created by the fan will be filled in the easiest way possible (conservation of energy). If its 2X easier to suck air through the side, you will get 2X as much air through that space as you will through an equivalent size grill opening. Thus, anything that prevents sucking air through the grills could have an outsized effect.
Last edited by getmygoat; Feb 27, 2024 at 08:41 PM.
That's an interesting possibility. I don't think its the forged pistons that have the problem - but the hypereutectic? (The top ring land is thin so it positions the top ring closer to the combustion and less shielded from its heat). I had a motor built wrong with those pistons. The real threat is you can get a piston to seize in the bore and it blows the top of the piston off. Bye bye motor. Luckily in my case I reviewed the spec sheet and was like WTF?
This is what worries me. The motor was rebuilt by a shop that went out of biz during covid. I have literally no information about the build details. The motor went to the shop without pistons or rods.
Long story. Didn't make the best choice of shop to work on this car in the beginning. Believe me, if I told you the story of what I've been thru to get this car restored and the $$ I've put into it, you would not believe it. I just have a thing for cutlasses.
Compression check seems ok - maybe a little low if anything. And the crank torque wasn't way high either.
Was thinking of a smaller diameter water pump pulley. Would help increase fan and pump speed which would help.
Was there an air dam along the bottom of the rad from factory that is present? I know air can be sucked from below also - and those lower dams can make a difference.
This is a little bit of a long shot - but those side openings could cause the fan to suck hot air from behind the radiator back through the radiator instead of forcing the air to come through the grills. Also - the partial vacuum created by the fan will be filled in the easiest way possible (conservation of energy). Thus, anything that prevents sucking air through the grills could have an outsized effect.
I hear what you're saying about hot air recirculating hot air back around to the front. The correct seals will be put on later this week.
Even with the hood up sitting still, it heats up to over 230.
I dont think there is an air dam under radiator front. A pic of what this looks like would be helpful. I will look into it more. Thanks...
Also used a thermal camera to see how the radiator was working. It was dropping the coolant temp by about 30 degrees from the inlet to outlet. So that seemed to be doing its job.
The front lower air dam is effective when the vehicle is moving - it creates a high pressure area to direct airflow into the radiator. It doesn’t really do anything when the vehicle is stationary.
The problem with the Speedpro pistons is the box says .001" clearance, the instructions say .002" and most say they should actually have .0045" clearance. It sounds like the big dish cast pistons were used especially if you have a stock replacement camshaft and low cranking compression. But you would think that it would run hot everywhere, if it was a piston issue. I had tons of running hot issues on my 88 Cutlass Supreme Classic Brougham. I tried different fans, thermostats and radiators. Bad parts like the Mr Gasket no flow thermostat and shitty fan controllers were frustrating. Getting rid of the under drive pulleys fixed the low speed/idling hot issues. If the seals don't fix it, try the pulleys I mentioned. What you running for timing and vacuum advance? You can get pretty aggressive with timing which might help a bit and make it more responsive.
The less coolant compared to water, the better the heat transfer; but, the coolant is needed to prevent corrosion and freezing. I'd first confirm the ratio by using a coolant tester and backing into the mix ratio needed to achieve the measured freeze protection.
WaterWetter may be used with or without coolant but it offers no freeze protection. It improves the ability of the liquid to transfer heat.
Another dumb test could be to just put a plug-in fan in front of the radiator on low speed and confirm temp stays down.
Easy enough to try i guess. Are you thinking this would this prove it to be an airflow issue? Its hard to distinguish between an airflow issue or coolant flow.
I wish I could decouple these problems to better diagnose.
I mean - i can really feel the current fan pulling air thru the radiator. I did put on an 18", 7 blade fan to improve airflow from the old 4 blade 18".
Easy enough to try i guess. Are you thinking this would this prove it to be an airflow issue? Its hard to distinguish between an airflow issue or coolant flow.
I wish I could decouple these problems to better diagnose.
".
I'm not sure it would prove anything if the temps dropped, why wouldn't they. If the temp didn't drop, that would be surprising and might be a clue.
Regarding the lack of spring in the lower hose, you'd want to verify no collapsing is occurring even at idle. The spring is there so the suction of the water pump doesn't reduce diameter of hose.
Return from heater core or transmission cooling, depending on where it comes from (if comes from firewall its heater core. If it runs down below engine to trans - well, then its trans cooling)
Sorry if my question(s) seem frivolous (perhaps meaningless). Do you ever experience ANY outflow from the radiator into the overflow tank when engine is idling? Either directly after shutting down after driving or while the engine is sitting at idle for an extended period of time? I suspect if there is never any coolant from the radiator into the overflow tank you have a minimum of 33% coolant w/ a (minimum) 4 psi radiator cap. You (should) most likely have a 15 psi radiator cap (you said earlier you think you have a 50% mixture). It doesn't hurt to ask whether your system is puking since I haven't seen it addressed in earlier posts. If, by chance, you are puking then refilling each time, it's a never ending battle which will continue. Just trying to garner a further understanding.
Sorry if my question(s) seem frivolous (perhaps meaningless). Do you ever experience ANY outflow from the radiator into the overflow tank when engine is idling? Either directly after shutting down after driving or while the engine is sitting at idle for an extended period of time? I suspect if there is never any coolant from the radiator into the overflow tank you have a minimum of 33% coolant w/ a (minimum) 4 psi radiator cap. You (should) most likely have a 15 psi radiator cap(you said earlier you think you have a 50% mixture). It doesn't hurt to ask whether your system is puking since I haven't seen it addressed in earlier posts. If, by chance, you are puking then refilling each time, it's a never ending battle which will continue. Just trying to garner a further understanding.
Sorry if my question(s) seem frivolous (perhaps meaningless). Do you ever experience ANY outflow from the radiator into the overflow tank when engine is idling? Either directly after shutting down after driving or while the engine is sitting at idle for an extended period of time? I suspect if there is never any coolant from the radiator into the overflow tank you have a minimum of 33% coolant w/ a (minimum) 4 psi radiator cap. You (should) most likely have a 15 psi radiator cap (you said earlier you think you have a 50% mixture). It doesn't hurt to ask whether your system is puking since I haven't seen it addressed in earlier posts. If, by chance, you are puking then refilling each time, it's a never ending battle which will continue. Just trying to garner a further understanding.
At first when after we started to run the motor after the rebuild (all old cooling equipment), it did spit back out of the radiator. Little did I know what the issues were gonna be, I added the overflow tank and adjusted the timing better, sealed all the vacuum leaks.
It had many issues at first. Also, i didnt have a temp gage back them so I had no idea what temp it was running besides monitoring with an IR sensor.
After I put in the new radiator, water pump, thermostat and fine tuned the timing - it has not spit back. It just slowly creeps up to 230° after about 15-20 minutes of idling. It used to be 5-10 mins, so we have made some improvements.
What I cant figure out is why this is still running hot after idling. As soon as I drive, temps come right back down to normal.
Was thinking about a smaller diameter pully on the water pump. This would both increase coolant and air flow which might be enough to get over the hump.
Any comments or suggestions appreciated on this strange issue. It only has about 50 miles on it after engine rebuild.
It was doing the same thing before without the clutch. Original config was no- clutch and 4 blade fan. Changed that all out to a
7 blade (same O.D. of 18") with clutch. Added the clutch because I accidentally bought the fan for a clutch application.
Oldsmobile has many different water pump pulleys depending on the year, engine and options such as AC, PS and HD cooling.
According to the 1972 PIM the correct pulleys for a 72 with a 350, no AC and PS are one of two following depending if you have HD cooling or not.
As you can see below the pulley size varies substantially.
Great info thanks. I believe I have a KN now (its a 2 groove), although i thought it was a 6". Will have to remeasure.
Going to a small diameter may help with this issue as long as 2 of the grooves line up.
If your PS pump is original, take a look at the code on that pulley. If it's a KG (possibly a single groove) or a KH (maybe a double groove) that could narrow down which water pump pulley your car originally had.
I simply measured the pulleys outside diameter.
If your PS pump is original, take a look at the code on that pulley. If it's a KG (possibly a single groove) or a KH (maybe a double groove) that could narrow down which water pump pulley your car originally had.
I simply measured the pulleys outside diameter.
I dont know originality of the pump. I do know that its a 2 groove pulley. Will look for a code on it.
