Summershandy

Straight 8 engine overheated at idle

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I'll give a little history. Year and a half ago, engine was flushed, distribution tube in great shape, hoses replaced, new thermostat and water pump and rad looks clean. Since I got my temp gauge rebuilt, while driving I can watch the needle get just past the halfway mark and see when the thermostat opens. The needle goes back down. I've been cruising like this for the past couple months. I entered my first car show of the year and had to crawl if not stop in a what seemed a quarter mile line for about 45 minutes. All the time watching the temp needle go up and up. The line kept moving so I couldn't turn the engine off so I would put it in neutral waiting the the thermostat to open and have the needle go down. It finally climbed to the top of the gauge before I could park. My heart sank. I turned it off and the rad boiled over. I didn't even want to tell anyone that in my glass bowl fuel filter it appeared the gas was literally boiling! What the hell?? I also grabbed a hold of the lower rad hose that was just a little warm. Do I have a thermostat issue? I nervously drove home after the show only to watch the thermostat open once again and keep the needle about half way on the gauge once again. I'm not planning on adding any electric fans or changing out the current fan with more blades. I know these engines run warm but just wondering what might have happened. 

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Perhaps you should have left it running for a while when you parked - to get it to cool down slowly. Shutting off a boiling engine is not good for it.

 

I drive city buses and it is common in the summer for them to get hot, especially climbing a hill. First piece of advice from the controller to non-mechanically-minded drivers is 'leave it idling when you stop'.

 

It is the winter here at present. Not that cold but still near freezing temperatures late at night. Leave the bus running at the end of a run to keep some temperature in the cabin heater and the engine temperature cools right off. Caught between a rock and a hard place.

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Interesting that you say the lower hose was only "warm" . Usually this would indicate that the radiator is doing its job quite well, if the rad is doing its job you should typically see a temp drop of 20 - 25 degrees F between the upper and lower hoses, perhaps this is something you could check with one of those infra red guns ?

 

Assuming this were the case, then maybe the thermostat isnt actually opening far enough to let full flow through the radiator at the extreme end of its scale ?

 

Having said this, straight 8s are notorious for heating up at the back of the block, maybe invest in an infra red gun and work your way around the engine with it to see if there are any hot spots, particularly at the back of the block.

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Posted (edited)

If it keeps cool at driving speed, probably more a air flow through the radiator issue. 

Edited by maok (see edit history)

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50 minutes ago, nzcarnerd said:

Shutting off a boiling engine is not good for it.

I agree but when do you shut it off? When it quits? I panicked somewhat.

38 minutes ago, hchris said:

Having said this, straight 8s are notorious for heating up at the back of the block

Interesting you should say that as that's where the temp probe is.

41 minutes ago, hchris said:

Interesting that you say the lower hose was only "warm" . Usually this would indicate that the radiator is doing its job quite well

But shouldn't that cooler coolant belong in the engine? Made me think the thermostat wasn't opening. Why did it not open?

 

30 minutes ago, maok said:

If it keeps cool at driving speed, probably more a air flow through the radiator issue. 

Agreed, I've been told to get a different size rad, electric fan or a fan with more blades. Just waiting to hear something different that may have happened. 

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A quick and simple test is run it without the thermostat and see if it stays cool or not.

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7 hours ago, Summershandy said:

I agree but when do you shut it off? When it quits? I panicked somewhat.

Interesting you should say that as that's where the temp probe is.

But shouldn't that cooler coolant belong in the engine? Made me think the thermostat wasn't opening. Why did it not open?

 

Agreed, I've been told to get a different size rad, electric fan or a fan with more blades. Just waiting to hear something different that may have happened. 

 

The coolant passing through the lower hose presumably is showing that the radiator is doing it's job, in your case the question is then, how much coolant is passing through the radiator  ?

 

Is the thermostat not opening enough or creating some other form of restriction to limit the volume of coolant passing through the radiator,  perhaps as someone has suggested, temporarily remove the thermostat completely and see what happens. 

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5 hours ago, hchris said:

Is the thermostat not opening enough or creating some other form of restriction to limit the volume of coolant passing through the radiator,  perhaps as someone has suggested, temporarily remove the thermostat completely and see what happens. 

 

I was just telling my wife, when I first got the car years ago I was unaware of CPR. I had picked up a new water pump off ebay and had difficulty finding a thermostat locally. My buddy at NAPA gave me one that was used in Chevy trucks. It "just" fit the large opening on the engine without falling through. I always had fit and operating concerns. I'm thinking the same, remove to test and inspect and while I'm at it, maybe get the correct one. 

Manual states, "six cylinder uses 151 degree and eight uses 160 degree. If permanent (ethyl-glycol) anti-freeze is used, a higher opening thermostat may be used." I pulled out my NAPA receipt and I see I'm running 180.  

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The Pontiac service manual makes notes of  testing 151 - 160 & 170 degree thermostats. CPR offers a 170. Wonder if I should step mine down 10 degrees. 

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Did you increase idle speed while you were sitting in traffic? Sometimes I find that putting it in neutral and increasing idle speed helps because it moves more air through the radiator and speeds its movement through the system. Not a whole lot faster than idle, but maybe 1500 RPM or thereabouts. The added airflow usually offsets the added heat from the faster operating speed. It's still not under load so it doesn't make much extra heat to spin it a little faster.

 

The fact that your lower hose was only warm puzzles me. I'm inclined to agree with your assertion that the thermostat might not be doing its job, or perhaps it's opening but not far enough for full flow at idle. At speed, there's more pressure to push the coolant past it, but at idle, maybe it's just too big a restriction. Changing it out for one that is known to be correct for that engine would be a good first step and see if things improve. A cooler thermostat won't help keep things cooler, it just opens earlier. Thermostats only set the MINIMUM operating temperature, but it's still up to the radiator to remove the heat.

 

Any car will heat up sitting still, so that's normal. The fact that it got that hot, however, suggests something might be amiss. Start with the thermostat, but if it happens again, experiment with keeping your foot on the pedal to bump up engine speed and see if it helps.

 

Keep us posted!

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3 hours ago, Summershandy said:

The Pontiac service manual makes notes of  testing 151 - 160 & 170 degree thermostats. CPR offers a 170. Wonder if I should step mine down 10 degrees. 

Changing the thermostat will have no effect on your overheating problem, UNLESS the thermostat is not opening properly. The temperature rating of the thermostat is the temperature at which it opens up and determines how fast the engine comes up to operating temperature, that’s all. I think you have a water circulation problem. You stated that the engine was boiling over and the lower hose was “just a little warm”. If the water in the engine is 212 degrees F the lower hose should be to hot to touch. You also stated the radiator “looks clean”, what does that mean? I’m leaning toward a bad radiator. 

 

Steve

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Posted (edited)
12 hours ago, Summershandy said:

 

I was just telling my wife, when I first got the car years ago I was unaware of CPR. I had picked up a new water pump off ebay and had difficulty finding a thermostat locally. My buddy at NAPA gave me one that was used in Chevy trucks. It "just" fit the large opening on the engine without falling through. I always had fit and operating concerns. I'm thinking the same, remove to test and inspect and while I'm at it, maybe get the correct one. 

Manual states, "six cylinder uses 151 degree and eight uses 160 degree. If permanent (ethyl-glycol) anti-freeze is used, a higher opening thermostat may be used." I pulled out my NAPA receipt and I see I'm running 180.  

 

Yes, removing the thermostat in itself is not a fix but will be interesting to see if it makes a difference. 

 

Whilst you have it out put in a pot of water and heat up to see how far it opens. If you suspect  a "fit" issue then that definitely needsto be sorted.

 

 

 

 

 

Edited by hchris
Word change (see edit history)

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Posted (edited)
On 7/27/2019 at 1:58 PM, Summershandy said:

I'll give a little history. Year and a half ago, engine was flushed, distribution tube in great shape, hoses replaced, new thermostat and water pump and rad looks clean. Since I got my temp gauge rebuilt, while driving I can watch the needle get just past the halfway mark and see when the thermostat opens. The needle goes back down. I've been cruising like this for the past couple months. I entered my first car show of the year and had to crawl if not stop in a what seemed a quarter mile line for about 45 minutes. All the time watching the temp needle go up and up.

 

This sounds fairly normal to me. Many old cars cannot do this trick very well. My 1936 6cyl runs 180-190 all the time, and doesn't even have a thermostat in it. It should have the 151F unit, and I have bought it one, but I don't expect it to change anything.

 

If the thermostat DIDN'T open, then it is defective, but I suspect you just exceeded the capacity of the cooling system, and so couldn't see when it opened. You could boil it in a pot, or just replace it. My six takes a thermostat that shoves up inside the thermostat housing, and is held in there with a retainer ring about an inch high. I thought all flathead Pontiacs had that setup. Does yours?

 

Everything is a tradeoff. Getting air through the radiator is the most important thing. At speed the fan is unnecessary, and just tends to block the radiator. If you add more blades, it would help at idle, but tend to block the radiator more at speed. More fan capacity also makes a bunch more noise at highway speed and eats horsepower. Pontiacs idle real slow. That doesn't help with slow speed cooling. Fan shrouds help a lot at low speeds, but tend to block part of the radiator. Some guys add an electric fan for stop/go traffic, but I suspect they are making things a lot worse at high speed. Most of the available fans are the photogenic ones with a bunch of tiny blades. Just look through one. It blocks almost the whole area it covers, and the fan wont help you at speed.

 

I took my six on a tour over a mountain in 106F, and got caught behind a couple of really slow(er) cars. It passed the 212 mark on the gauge, and eventually almost pegged. On the way back the same thing happened, and I was near pegged and not even halfway up the hill. I had to leave the group for a bit and go get some air through the radiator, and then come back. I never boiled or spilled any coolant, but it had to be right on the edge! Lots of the other cars in the group did boil that day.

 

On 7/27/2019 at 1:58 PM, Summershandy said:

The line kept moving so I couldn't turn the engine off so I would put it in neutral waiting the the thermostat to open and have the needle go down.

 

Yeah, that sucks. Revving it up while in neutral will make the fan do more.

 

On 7/27/2019 at 1:58 PM, Summershandy said:

It finally climbed to the top of the gauge before I could park. My heart sank. I turned it off and the rad boiled over.

 

As soon as the water pump stops turning, the coolant flow is drastically reduced. In my area, summers are HOT, and shutting off a hot car was always a no-no, unless you know it is broken and you know it isn't going to come back down. Assuming its still full of coolant, rev it up a little to circulate the coolant around before shutting it off. Even idling is better than shutting off, and would be fine on a car that isn't lacking fan capacity.

 

I seriously doubt you hurt anything. It didn't boil until you shut it off. It probably wasn't THAT hot.

 

On 7/27/2019 at 1:58 PM, Summershandy said:

I didn't even want to tell anyone that in my glass bowl fuel filter it appeared the gas was literally boiling! What the hell??

 

That isn't good, but if you didn't get sidelined with vapor-lock/percolation, then that is good. I hear the glass bowl fuel pumps are worse for it. I have not been sidelined yet, at least since returning the fuel system to stock, even in 106F, though one time it did start to run a little flaky for a block or so. Just enough you could tell the fuel system was way too hot.

 

On 7/27/2019 at 1:58 PM, Summershandy said:

I also grabbed a hold of the lower rad hose that was just a little warm. Do I have a thermostat issue?

 

Maybe. I would boil it or just replace it. I think the original has a bleed hole in it, and if the new one doesn't I would consider adding one.

 

14 hours ago, Summershandy said:

Manual states, "six cylinder uses 151 degree and eight uses 160 degree. If permanent (ethyl-glycol) anti-freeze is used, a higher opening thermostat may be used."

 

The lower temp thermostats were necessary for Alcohol antifreeze.

 

Edited by Bloo (see edit history)

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Posted (edited)

Early Times Chapter on the subject of engine temperature:

 

Quote

 Engine overheating tops our informal, non-scientific poll of concerns that keep ETC member cars close to home.  Whether your Pontiac simply registers a high temperature on the gauge under certain driving conditions, or if it actually “boils over” and leaves you stranded by the side of the road, this article should cool off both car and driver.  Unless your ETC era Pontiac is completely out-fitted with the taxi or police special equipment, it was never intended for “parade” use and will certainly register higher temperature in stop and go traffic, even it does not lose any coolant.  So our first issue is to determine how hot is too hot.

Maximum Safe Operating Temperature

  The maximum safe engine operating temperature is more dependent upon the type of anti-freeze and engine oil used, than the basic materials and construction of the engine.  Even as late as 1954, alcohol anti-freeze was still in common use; but alcohol has a boiling point lower than plain water and could not be used during summer months.  It also required lower thermostat operating temperature, a 151 degrees was standard, to prevent the alcohol from literally boiling off during normal driving.  I sincerely doubt any of us are still using alcohol anti-freeze today.
  Ethylene glycol (Prestone) was available in the mid-twenties, but it was more expensive than alcohol and also had a couple of unfortunate tendencies.  The first of these is that it is much more likely to leak through hose couplings and gaskets than an alcohol mixture.  The second issue is that it is more likely to loosen rust and scale in the cooling system and could lead to restricting the flow of coolant through out the entire system.
 Another unfortunate circumstance surrounding ethylene glycol was the way it was often marketed; since it had a much higher boiling point, it could be left in the cooling system year around, hence the term “permanent” anti-freeze.  Unfortunately, because of its higher cost, early motorists would have it installed and never change it again, mistakenly believing it was “permanent”.  I recall older customers coming into my father’s service station to have their car winterized and readily accepting any ethylene glycol anti-freeze except Prestone because they had, or knew someone who had, a bad experience due to “Prestone” that was never changed and rusted out the cooling system!
  I believe it is safe to assume that all of us who use anti-freeze in our car use ethylene glycol in a 50-50 mixture.  This solution raises the boiling point above that of plain water; none of us has to worry about “boiling-over” when running as high as 220 degrees.  If you also run a pressurized radiator cap, which the majority of our Pontiacs’ featured as standard equipment, the boiling point is even higher.  A high temperature reading on the gauge deserves to be watched closely; but if there are no other symptoms of overheating, and if it appears you will soon be moving again at even low speed, you are better off continuing to drive with the expectation the temperature will drop back to normal readings with normal driving.  If you come upon an unavoidable situation in completely stopped traffic, you may have no option but to pull over and shut off the engine until the flow of traffic resumes again.  This would not have been considered “abnormal” even in the fifties; and it does not represent a failure on the part of your vintage Pontiac.  Our Chieftain is good for about 90 minutes in seriously heavy stop and go traffic; the temperature gauge running dead on HOT for the final 15 minutes without any boil-over.  I leaned this by unfortunate experience, but you could certainly idle your car around your own neighborhood on a hot summer day and learn how much is too much without being stranded far from home.

 

More Here: https://web.archive.org/web/20171010103648/http://www.earlytimeschapter.org/coolingsystem.html

Edited by Bloo (see edit history)

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Thanks for that article. When I got the car it had an aftermarket temp gauge where as it could see the actual engine temp on the gauge. Providing it was correct. My new rebuild is original and was calibrated to be 180-190 halfway. Hard to say what the "hot" mark would actually be. I did put the car in neutral every stop and picked up the idle to get things flowing. Maybe it helped, maybe it didn't. The thermostat placement is pretty basic. No retainer ring unless I'm missing it. I flushed my rad when I had it out. It ran clean and visually looking from the top looks in good shape. Not to say something's plugged where I can't see. 

What does the bleeder hole in the thermostat accomplish? I've read of guys actually adding one. I also understand the purpose of thermostats and that changing operating temp doesn't change any over/under heating issues. 

Just a note that I was not the only one overheating that day. Mind you, the cars that did had performance engines in muscle cars and that's a different animal. I'm still going to open things up when my new thermostat comes in. Thanks for your comments gang! Very informative.

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9 hours ago, Bloo said:

retainer ring about an inch high.

Hey Bloo! Looking at the CPR catalog they list a stainless retainer ring for 1933-54 pontiacs. Guess I should order one and take if from there. 

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28 minutes ago, Summershandy said:

Thanks for that article. When I got the car it had an aftermarket temp gauge where as it could see the actual engine temp on the gauge. Providing it was correct. My new rebuild is original and was calibrated to be 180-190 halfway. Hard to say what the "hot" mark would actually be. I did put the car in neutral every stop and picked up the idle to get things flowing. Maybe it helped, maybe it didn't. The thermostat placement is pretty basic. No retainer ring unless I'm missing it. I flushed my rad when I had it out. It ran clean and visually looking from the top looks in good shape. Not to say something's plugged where I can't see. 

What does the bleeder hole in the thermostat accomplish? I've read of guys actually adding one. I also understand the purpose of thermostats and that changing operating temp doesn't change any over/under heating issues. 

Just a note that I was not the only one overheating that day. Mind you, the cars that did had performance engines in muscle cars and that's a different animal. I'm still going to open things up when my new thermostat comes in. Thanks for your comments gang! Very informative.

 

Drilling a hole in it allows air pockets to move past the thermostat even when it's closed. Sometimes you'd get a big air pocket that would never get hot enough to open the thermostat even though the coolant behind it was boiling. Air is a notoriously poor conductor of heat (which is why it's the best insulator). Just a small 1/16" hole is all you need to let air pass the thermostat when it's closed.

 

I'm still puzzled about the cool lower hose and I'm still leaning towards thermostat. If the car otherwise operates properly and to the point where you can see the thermostat opening and closing, then the radiator must be rejecting plenty of heat. It's a little strange that idling would not allow the thermostat to open, but I think you're on the right track so it's good to start there--at least it's easy to reach!

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1 hour ago, Matt Harwood said:

I'm still puzzled about the cool lower hose and I'm still leaning towards thermostat.

So am I. I would have thought after a couple of cycles of the thermostat, that lower hose would be much hotter than it was. Even if an engine was operating correctly, hoses should be hot to the touch. I could grab on to it and hold it with no discomfort. 

And yes, this thermostat is the most easiest to work on!

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CPR informs me that they carry the thermostat retainer but it's a bit too long and has to be trimmed down. That's interesting. They also have NOS 160 degree thermostats that apparently allow more coolant to pass through them. I told them to ship them. We're only talking 10 degrees either way. 

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5 hours ago, Summershandy said:

Hey Bloo! Looking at the CPR catalog they list a stainless retainer ring for 1933-54 pontiacs. Guess I should order one and take if from there. 

 

Stainless sounds like a good idea.

 

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The thermostat crams up inside the housing, and you need the ring to hold it in. That confused me at first because there was no "shelf" at the flange like you usually see. The thermostat in the pics is almost certainly aftermarket, but I have seen an original Harrison one out of a 37 Buick Roadmaster and it looked nearly identical. It had a bleed hole just like this one does.

 

I doubt it is necessary to have the original type, this one just happens to be. EIther way, make sure the temperature sensing element (the bellows on this, or the copper pellet on a modern stat) is pointed to the hot water.

 

 

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Found these pics and this is what I should be getting. My housing doesn't look like this but is only for example. I see now where it needs to be cut. 

 

 

 

 

 

 

s-l1600.jpg

s-l1600 (1).jpg

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I have a 1953 Pontiac 8. I drive it all the time in nice weather. I use it when it's 20 degrees and I use it when it's 95 degrees. The temp gauge needle in the summer will stay around the halfway mark in normal driving. If it's stop & go or I park it and then restart the car the needle will go slightly above halfway. When I get moving again it goes back down to half. In cold weather it's about at the 1/4 to 1/3 area. I just returned home from a 10 mile trip. It's 92 degrees here now. I cannot touch the lower hose with my hand for more than a second as it's too hot. I have never used it in a parade or for a long time in stop & go driving but I think the needle would go closer to H if I did. The gauge has never been on H or overheated since I've owned the car the last 8 years. I THINK there's a 180 thermostat in it.  Just relating my experiences, hope this helps somehow!

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1 hour ago, Summershandy said:

My housing doesn't look like this but is only for example

My apologies, I raised my hood to show my wife about the thermostat and was pleasantly surprised to see this IS my housing. My current thermostat sits below in the block and not so much in the housing. I'm looking forward to getting this right.

1 hour ago, The 55er said:

Just relating my experiences, hope this helps somehow!

Every bit helps! Thanks 55er much appreciated. Without stories such as yours I wouldn't have a clue! 

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Your thermostat wouldn't be sitting in the block, the cylinder head yes, the engine block no.

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Yes, head not block. Goes to show I haven't done an engine rebuild yet! Did I make your head shake a bit Charles? LOL!

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