rhodyrocket2

Hey all


Been dealing with this issue for a year, but no improvements. 180 degree thermostat, 6 pound radiator cap. Fan and clutch seem fine. Had the radiator flow tested, fine. Removed AC "radiator" in case it blocked airflow. Engine not a rebuild, maybe over 100k miles? I had changed water pump 10 years ago.


Car runs fine, set to factory specs. It used to puke coolant when shut down after a medium drive (20 miles) for years. I just added coolant, but suspected some problem. I added a puke tank and a gauge about a year ago. Now I see what happens and I made those changes in previous paragraph.


When I drive it goes up to 180 for about 20-30 minutes, then climbs. Generally up to 200, sometimes 220. It doesn't boil over, but I don't drive long distances. When shut down, it has puked a little into tank (pint?) and then it pukes about a quart into the tank. It seems that highway driving speeds makes this happen. I can let it sit at idle for about 45 minutes and it stays at 180-190. I rarely drive more than 30-40 minutes. I checked the gauge, it is accurate. And it doesn't get above 90 degrees out here. So I am generally driving in weather 70-85 summer weather. I do think it would boil over on a long trip or in hot weather.


This all makes me nervous driving, watching the gauge. I seem to have run out of ideas. I do not want to rebuild the engine for a possible head gasket, its an $$ option.


I was thinking of a 160 degree thermostat and new cast steel water pump and possible add a electric push fan to go on when it is over 180 degrees. It does have a more powerful alternator. But keep the stock fan too. But technically I doubt a fan will really help at highway speeds anyways. There should be enough airflow without a fan.


So any advice, thoughts would be helpful!

oldcutlass

It sounds like a tuning issue, possible timing chain, or maybe a bad head gasket.

Gary M

Check tuning

Check compression in each cylinder to check for head gasket blown.

Do you have the fan shroud on and is the fan located at the edge closest to the motor?

Do you have a spring in the bottom radiator hose to keep it from sucking shut? Squeeze the hose while motor is cool, if it squeezes easy probably has no spring

^^^^^^^ definitely do this one^^^^^

Fun71

It could simply be your engine is generating more heat at highway speeds. My car runs all day at 180º in 110+ summer temps with the AC on, but if I drive on the highway at 70 mph the temps climb up into the 210+ range. This is due to the elevated RPM during highway driving (3200-3400 RPM) generating more heat. If I slow down to ~2800 RPM, the temp drops back to 190º.

So, what is your highway RPM?

Gary M

If it can idle with no overheat skip the fan idea. Definitely check the lower radiator hose for a spring though. Higher speeds may suck it closed and cut flow.

AZ520

http://www.rockauto.com/en/moreinfo....c=2778&jsn=614

brown7373

Is your vacuum advance holed up and working?

chopolds

If it heats up while driving, it's usually a water flow issue (assuming engine condition/tune is good). you had your radiator tested...usually they only pressure test it. Doesn't mean it's flowing though all the tubes. Could also be the water pump. 10 years is a long time, esp. if you used a rebuilt unit! I'd buy a cheap infra-red non-contact temp gauge. Run it hard on the highway until hot, then use the gauge to check for hot and cold spots on the radiator. Could be clogged.

rustyroger

Sounds like a classic partially plugged radiator to me. Thousands of these cars ran fine at highway speeds back in the day with no problems. It could be the water pump impeller has worn, but if it was my car I would have the radiator re-cored.
It has solved many overheating/mystery water loss issues many times for me, this in England where temperatures above 85 degrees make the national news.

Roger.

joe_padavano

More like HUNDREDS of thousands. These cars did not overheat from the factory and did not need electric fans. They were designed for and tested at the GM Proving Grounds in Arizona in the summer. Fix what is not correct, don't bandaid a problem.

Also understand that these cars were tuned for the gasoline of their time. Today's ethanol-laden gasoline results in a leaner mixture, which can cause overheating. Old, incorrectly functioning vacuum advance, stretched timing chain, and partly plugged radiator can all contribute to the problem.

MDchanic

Why on earth are you running a 6 pound cap?

- Eric

joe_padavano

Likely because he missed the "1" before the "6" when typing...

m371961

MD, I was wondering the same thing.

oldcutlass

I ran a 7 psi cap on my Plymouth with a 160* thermostat and a catch can, never had an issue.

Fun71

I currently have a 7 psi cap on my Cutlass. Less pressure in the system for reduced stress. If it doesn't boil over with a 7 psi cap during our 115+ degree summer temps, then a 16 psi cap is just overkill.

MDchanic

You all will recall that there are certain phrases that seem to be repeated on this board over and over through the unlimited expanses of time. Things like, "It didn't overheat when GM made it," and "GM didn't spend the extra money to create and install parts for no reason."

Throughout the '30s and '40s, most cars used 4 pound or 6 pound radiator caps.
As the fifties went along, 15, 16, and 18 pound caps were introduced.
Go out and look at your modern cars. Pop the hood and look at the radiator cap (that is, if you can find it). Tell me if it isn't 16 or 18 psi.

This didn't happen because engineers were fond of higher numbers, or thought that higher pressures would impress the heads of their design teams. It happened because it provides improved heat transfer, and therefore allows the company to save money by using a slightly smaller cooling system, and by reducing warranty calls through fewer problems caused by "hot spots."

Higher coolant pressures, in addition to raising the boiling point of the coolant in a general sense, do something much more important: They reduce micro-vaporization, or tiny pockets of boiling or steam, at the junction between the hottest surfaces inside the cooling system (the sides against the combustion chambers). These areas of microscopic boiling produce a heat-insulating barrier between the head and the coolant, reducing cooling efficiency, and doing so at the worst possible time - when the heads are the hottest. By reducing this insulating effect, you reduce local overheating and improve overall cooling (especially under conditions of high output).

Yes, the cooling system will cool at lower pressures, but it will not cool the way it was designed to, and it will not cool as well. If your coolant temperature goes down with a lower pressure cap, it is because the heat is staying in the engine, and not getting to the coolant.

- Eric

oldcutlass

I understand what your saying Eric. The cap has nothing to do with any of the above if it does not lose pressure, its a safety device. The system is working as designed.

MDchanic

As you like to say about thermostats, Eric, the cap doesn't create the pressure, it just regulates the maximum that the pressure can get to.

My point is that the higher the pressure, the more effective and efficient the cooling, and if you choose to use a cap with a lower pressure that specified for the system, you are reducing the system's cooling capacity.

- Eric

Gary M

So the cap determines the pressure of the system by slowly releasing pressure above what the cap is rated for, not just when it overflows?

edit: I really need to type faster

oldcutlass

My temps were always 170*, 190 in traffic, it would run all day without puking. The cap was chosen because the original down flow radiator that I had recored still had 50 year old tanks. There was no need for the increased stress in case it wanted to overheat.

MDchanic

Yes. It begins to leak just the tiniest bit as the pressure approaches its specified limit.
That's why they use overflow tanks - the small amount of vapor that is released is released into the coolant at the bottom of the tank and condenses back into a liquid, then as the engine cools, the cap allows it to suck the same amount of coolant back in.
A system without an overflow tank will very slowly lose coolant and need to be replenished more often.



Right. But you thought about it and had a logical reason to use one, and understood that you were using a non-specified part.

- Eric

Fun71

Nope. It's 21 psi.


I completely agree with you about the cap pressure, but as oldcutlass said, since my car doesn't overheat in 115+ ambient temperature with the AC on, I do not have any cooling problems and don't need a higher pressure cap. If my car had overheating issues, then I would definitely use a different cap, and I recommend that anyone who is having overheating issues should use a 15-16 psi cap.

Gary M

I still want to know if his lower hose has a spring in it. Sorry- inquiring minds want to know

rhodyrocket2

Hey guys
Thanks ALOT for your suggestions. I have not driven it because of weather.


1 Lower hose has a spring, but about 6-8 inches does not have spring. I may change it.
2 fan clutch. has a shroud, fan is in right place fan spins with slight drag when engine off.


I am going to drive it until hot. Use my friends infared temp gun to check radiator for hot cold spots. I will also see if clutch is engaged at hot temps.


Cap pressure. I know it is low, 6 or 8 psi. My gut feeling is that this is a head crack or gasket issue. Thought a low psi would not stress it. but no white smoke from exhaust or real coolant loss.


will post again with new info soon.


thanks again!

Gary M

Not sure they have a spring through the whole hose, that's probably not your problem.

Autozone, Oreilleys etc may have a compression tester in their free loaner program if you don't have one. Rule out as much as you can without spending any money. Good luck, keep us posted.

those parts stores do have a free rental tool you can hook on your radiator cap opening and run the motor. If the fluid in the tool changes color it's a sign of head gasket problems but you would then have to do a compression test on each cylinder to find the bad one.

olds 307 and 403

Definitely check all over the rad. Mine 88 heats up at highway speed and the rad is partially plugged. I actually plugged it with stop leak due to a leak between the cores. I am also running a 7 pound cap to keep it from leaking again, both cause the warmness at highway speeds. Having the 260 in the car now makes it liveable, requires less cooling. On a properly working system at highway speed, a fan is hardly needed, also check that all your air dams are in place. I have also had a Mr Gasket high flow thermostat close at Highway speed but could feel the flow at idle, caused me much grief.

brown7373

My Cutlass with A/C ran hotter than I wanted too. I switched to a Hayden 2705 clutch and have never had it run hot again. The book will tell you the 2705 is not for the Cutlass, but I have been running one for years. It is heavy duty and more heavy duty than the heavy duty that IS recommended for the Cutlass. It stays engaged longer before it cuts out, but it really pulls the temperature down and keeps it down. Of course it also helps that the rest of the cooling systems is in good order. My system was in good order, but still would creep higher than I wanted. The 2705 solved it.

Before you spend a lot more money and effort on non-original electric fans, consider spending $22.79 from Rock Auto.

rhodyrocket2

Hi All


Again, thanks for your help. I wanted to make a change and drive in hot weather. It has been cool weather here. Again, 1972 cutlass 350 4bbl. Always crept up temp with highway driving to 200-220. with 180 degree thermostat.


I changed the fan clutch.Hayden 2705 .


First day driving I did notice a change. Drove for about 45 minutes on highway, but cool day, 65 degrees. Temp went to 185-90 and stayed there. Never higher. I was encouraged. Before clutch it crept up to 200.


Today it was almost 90, so I wanted to a test drive. Temp stayed at 190 for 30 minutes driving to highway, as before. Drove on highway about 60MPH for about 45 minutes. Temps stayed at 190 for about half hour, then began to creep up to a little over 200. And stayed there. This was a little lower than I have seen driving at cooler outside temps with the old fan clutch.


I then drove regular roads for about 30 minutes. I figured the engine was full hot as it was driven on highway. Temp went down to 185-90 (never did that before always stayed up).


I then left car running at idle in driveway for a half hour. Temp crept up a bit, maybe 195.


I used infared gun to check radiator temps while running in driveway. I could not see any obvious deadspots in radiator. around 140, 160 degrees.


I also checked radiator hoses with temp gun. At thermostat housing, temp was like 190. upper radiator hose 180, lower radiator hose around 170.


Personally, I consider this acceptable, but not optimal. Todays drive was a little more than I usually drive. It was hotter outside and I drove a little more. But I would have liked to see it stay at 185-90 the whole time and not creep up to 200 on highway.


I would like your opinion as things are now, with this data.


I would also like to know what specs are for the distributor, to see if there is an issue at higher RPMs. Like vacuum canister advance and total mechanical advance. I was thinking the distributor could be too advanced, causing the higher temps at higher RPMs.


But my main question is your opinion on things as they are now. I don't want the spark timing to take over this thread.


Again, thanks all for your input so far! I don't think I have some major problem that needs a engine rebuild. Again, acceptable but not optimal.

oldcutlass

I can see changing your fan clutch making a difference at idle, however at highway speeds its strictly airflow blowing through the radiator as the fan does very little. Your temp numbers are normal with nothing to worry about. A 180* thermostat begins to open at around 180* and can take 15-20* to fully open, in addition there is a tolerance of a few degrees.

Read this link:
http://www.stant.com/index.php/engli...s-thermostats/

rustyroger

I don't think this is acceptable. the car shouldn't run hot with the cooling system in good order.
I will add a caveat here, are you running gas blended with ethanol?. Old fashioned V8s were not designed to run with it, I understand carburetors mostly run to lean without careful recalibration.

If the thermostat housing is at 190, surely the top hose should be the same temperature, it won't have had any chance to cool before entering the radiator. The high temperature of the bottom hose indicates not much heat is being removed in the coolants passage through the radiator.
Which leads me to believe the radiator core needs replacing. Not rodding out, but replacing.

Roger.

Fun71

What is your highway cruising RPM?

Here's something to consider: A co-worker had overheating issues on the highway only, ran cool at lower speeds. He eventually discovered a bunch of leaves in the corner of the gap between the radiator and the AC condenser. This was blocking air flow through the radiator, resulting in reduced cooling capability.

AZ520

This will fix you up!
http://www.championradiators.com/Old...ator-1966-1977

Cutlass Fan

Timing that is too retarded not too advanced can cause over heating. Like Oldcutlass said the fan should have minimal effect at highway speeds. I suspect you're rad isn't doing its job.

rustyroger

Did you fix it?. What did you do?.

Roger.