still overheating...

Dana Bennett

PCS Life Member
Hi all!!

I have been working on my '76 Cadillac hoping to be able to bring it to the International Meet. This coach has had a problem with running hot since I got it 11 years ago. I am just getting it back on the road after sitting for nearly 10 years due to this frustrating problem!!

Among the other things that I did to this car before I took it to the Kingston PCS Show in 2000 are as follows:

Flushed entire block and heater core, crawled under car and even removed the small threaded plugs on each side of the block.

Installed new radiator, I would have to check but I think it is only a three core as THAT is the radiator the parts store listed, I think the one that came out (I think I still have it as well) may have been a four core.

Installed new thermostate ( 190* I believe)

Installed new clutch fan

checked/adjusted timing (after replacing missing/broken plastic timing scale)

I just got plates and put it on the road and took Jill out for icecream last night (first time she has riden in it even though it has graced her garage for the last 10 years!! lol!!) and as expected it is still running HOT.

In getting her ready over the last several weeks coolant level and FLOW were checked and found to be fine.

There is no evidence of oil in the coolant nor coolant in the oil.

I installed some gauges (electric) and it seems to run between 200 and 210, and will gain about 20* after shut down.

1.) WHAT is an acceptable temperature for this engine (500 ci) to average??
I always thought it should run at the temperature of the thermostate.

2.) I have been told to REMOVE the thermostate completely, is this OK??!!
Will doing this do ANYTHING?? (car is NOT driven in winter.)

3.) I currently have 20w50 engine oil in it, would putting it back to 10w30 make ANY temperature difference??

4.) any suggestions?? I have had this car for SOO long and I just want to enjoy it!!!


The engine comaprtment gets very hot, the leading edges of both front fenders outside are very hot, passenger floor above Catylitic converter is also uncomfortably very hot (is not plugged as exhaust comes out just fine)

time is running short and I want to be able to go to the meet, enjoy the meet AND make it home safely!!

Dana Bennett.

see a few pictures of her on my facebook album

http://www.facebook.com/media/set/?set=a.1609218308788.177828.1186117691&l=3a4771a328

HTML:
http://www.facebook.com/media/set/?set=a.1609218308788.177828.1186117691&l=3a4771a328
 
The temp your telling that its running is about the norm it seems like. That's about what my 73 M-M with a 472 runs out at. It never boils over and will always start up fine each time and runs as smooth as a sewing machine at those temps. I to did the entire flush and thermostat replacement to and it still runs out at around 210-220 during normal driving. Just the nature of the big block Caddy engines!
 
Looked at the radiator on the 73 and mine is a 4 row core not a 3 row. You may want to upgrade to a 4 row and they are avalible at most parts stores too.
 
how is your radiator cap? A bad cap can contribute to higher running temps as well as a weak hose. What antifreeze dilution are you running? I run a 70/30 (30 percent water) ethyleneglycol
 
Jeremy, I too would figure big block cadillac to run hot as it IS a lot of engine!! lol!! but this just doesn't seem right and I'm guessing on a hot july day that this will probably be running even hotter than now maybe?? I will check the price of a 4 core at my local stores and see if I can get one.

Russ, HOW do I check if the carb is running too lean?? could that also make the catylitic converter seem hotter than it should be?? it does seem to run and drive fine, I did rebuild the carb years ago, when I got the car the back of the car was getting covered with black soot whenever it was driven, I think that kinda went away when I did the carb.

Kenn, I was wondering about the cap as well (although that also was replaced new when I did the radiator) because sometimes I can still squeeze the upper radiator hose some after it's been running. I am not sure what my mixture percentage is but typically I would put in two gallons of antifreeze and the rest water.
 
There are a few ways to check for a lean condition;
1. get the exh sniffed at a garage

2. Check the plugs for a tan look on the electrod. A clean or white look is a lean condition.

And always run with a thermostat.

Your anti freeze should be 50/50 mix.
 
if you think it's running to hot change out the thermostat. go to a 180 or 160. what you want is it to run at a constant temp. the new three row radiator will be good enough. a 50/50 blend is the most you need on the coolant. then drive the car, get use to it. the big thing is you not comfortable with it. they put those idiot lights not gages on it for a reason. they felt you didn't need to know what it was running at. a lot will depend on were you put the sending unit for the gage. the only way to tell just what it is doing is drive it till it's at running temp and use one of the no contact thermometers and check the engine. it may not be as hot as you think. a lot of the heat your felling could be off the manafolds.
 
I have a buick 455 that always ran hot . She was ok as long as she was moving but at idol the temp would keep climbing. I tried the no thermostat thing. IT DOES NOT WORK !!!!!!!!!!!!!!!!!!!!
Running without a thermostat made it take longer for the temp to go up, but it
also took longer to go down once it started moving again.

I ended up putting in a aluminum radiator and running just a strait fan with no clutch. Also a 160 degree thermostat. This made a BIG improvement.

She will still run hot at idol eventually but it will take A LOT LONGER ' much more reasonable. As for driving --- she runs at a steady 160 to 170 depending on how hot the weather is.

I feel your pain , i also did not drive her for several years because of this problem.
 
I can share this with you. I read that the lower radiator hoses can fail over time and even thou they are supported internally with a wire cage, they can collapse from the shear force of the water pump pulling water through the motor at such large volumes. B.S. or legitimate I found some merit in the observation and that lower radiator hose is one of the first items that was replaced on our 69. It was noted that this issue was a constant cuase for overheating, until it was discovered.
 
Dana, I have a 1980 Superior Cadillac hearse with the 368 engine. When I bought it, it had no catalytic converter on it, and it ran great. But it was not yet an antique when I bought it, so come my first state emissions inspection, they wouldn't pass it without one. So I had one installed, and suddenly the car ran like crap and hot. I tried all the basic fixes that have already been suggested, and nothing helped. I finally resigned myself to thinking this is just how the car is going to be.

Well after a couple years it came time to replace the exhaust system, and just on a hunch, I paid extra for a performance free-flow catalytic and muffler. That made all the difference in the world. Suddenly the car was back to the way I remember it being when I first got it.

A friend of mine with a more ordinary collector car complained about the same problem he was having, and I told him that putting a performance exhaust system on the car worked for me. He did the same on his, and it worked for him too.
 
Make a close inspection of the exhaust manifolds. Hairline cracks are hard to spot especially on the undersides, and they can be a big contributor to a hot running engine. I went through 2 sets of manifolds before replacing them with hugger style Sanderson headers. I also had the headers coated inside and out with a heat reducing coating by Caps Coatings.
 
I had overheating problems with a Packard engine. Replaced everthing and even removed the thermostat completly because they didn't come with thermostats. Still had overheating problems. Finally last July, the engine blew a rod bearing. I decided to have the entire engine rebuilt because they also found the pistons were tapered. During the rebuild they found rust and crud in the engine block that was not allowing the coolant to flow. Flushing the system was not enough to move this.
 
Some good points have been brought up. To elaborate on the thermostat, GM ran 190-195 thermostats IIRC to reduce NOX emissions. I would drop it back down to the 180 range as maximum and if that does not help, 160 degrees.

Distributor condition, such as a failed vacuum advance unit or worn out advance weights could be a factor here too. If all the emission related equipment, the TCS switch, etc, (as I forget all of them due to old age and not seeing them very often any more) has failed and restricting vacuum advance, this too could be a cause. Also check your timing and make sure that the harmonic balancer outer ring has not slipped on the inner hub putting the timing marks either advanced or retarded.

Built up sludge in the block could too be a cause. MAYBE by knocking out the block freeze plugs you MIGHT be able to get some of the sludge out. If you have my luck it will not work though.

Also, is the fan clutch working? If it is a replacement, is it a thermal or a non thermal? Could be a cause too.

You might look at this web site too:http://www.haydenauto.com/Featured Products-Fan Clutches and Fan Blades/Content.aspx

Also, failure of a water pump or a incorrectly rebuilt water pump could be it.
An impeller slipping on the shaft, the wrong impeller or a impeller improperly installed (fins facing the wrong direction) could be it too.
 
One thing I forgot about the thermostat. It is a restriction device to keep the coolant in the radiator longer allowing more heat dissipation. Without a thermostat, the coolant can literally go through too quickly at high engine speeds. And cavitation can occur too with air pockets. More air pockets equals less coolant to dissipate heat too.
 
WOW!!!!!


So many great replies!!!!
Thanks everyone and now I have many things to look at!!

I will try putting in a 180* thermostat to begin with and monitor the lower Rad. hose. (figure it's better to start with the simple things!!lol!!)

and yes, as is typical I guess with cadillacs, I DO have cracked exhaust manifolds!!!! I will look into those headers (although if it is anything like trying to get headers for my '73 Buick LeSabre with a 455 I quickly found out that they were WAY out of my price range at $600 to $900!!!!) but if not then I DO want to replace the manifolds!!

Being that I am in NY I think I HAVE to have the catylitic converter on it, but would love to remove it!! ( Plus I think I would like dual exhaust!!)

If I decide to swap out the clutch fan for a direct drive (would like to do an electric someday if that would work??!!) then what can I take the direct drive fan from?? I think my '74 472 was a clutch fan and I think most of my other big blocks are clutch fans as well but need to check, is it basically just a GM part that will bolt in from most anything else??

Awesome!! Thanks everyone for your welcomed words of wisdom!!!

Dana Bennett.
 
most all your early 70's were a flex fan on the CC. at HY speed the fan is a none issue as the ram effect takes over. the hot your felling under the hood is the cracked manifolds for sure they will run the engine bay tem way up there. if you do change the converter, only do the converter to the high flow one. that will keep you car quite. we did this on the 89 6 door with the 305 and it really helped the power. but the first thing I would do is change the manifolds or get the ones you have repaired. which ever is easier for you. a good welding shop can weld the cracks up them you need to get them plained before you put them back on. it might be cheaper to just replace them then do that. till you do this you will be figting hot under hood tems.
 
I can share this with you. I read that the lower radiator hoses can fail over time and even thou they are supported internally with a wire cage, they can collapse from the shear force of the water pump pulling water through the motor at such large volumes. B.S. or legitimate I found some merit in the observation and that lower radiator hose is one of the first items that was replaced on our 69. It was noted that this issue was a constant cuase for overheating, until it was discovered.

All the new lower radiator hoses don't come with the wire in them .. Cost savings at its finest...:alc:
 
sorry it is very late here , i wanted to say that does not surprise me.

I would also not recommend just using an electric fan. I ran one puller behind my radiator and a small 8 or 10 inch fan on the inside of my grill. It did nothing to help the problem. I ended up running a 14 or 15 inch flex fan that i bought from jegs. I simply put some long bolts into ware the fan would connect to the water pump (sorry i don't remember what that part of the pump is called) and used a couple of nuts for the desired length of spacers. That flex fan made a huge difference. I hope i did not mess up that description to bad . I just do it and am not to good with the names of the little parts. I am also up very late here :confused::confused::confused::confused:
 
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