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70 Deville Overheating and AC

Started by Houston747, December 16, 2021, 12:12:25 AM

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Houston747

I have a 70 Coupe Deville, and I wanted to see you guys experiences with the AC and overheating in your Cadillacs. I have a what appears to be a stock 3 row copper radiator on my Cadillac with a 160F thermostat, I just got some work done on the car along with the new 160f thermostat. I know my radiator is blocked with some calcium which I am planning to get cleaned up ASAP, and that might be restricting some water flow, but for some reason driving the car now it runs at about 150-170f and if I were to turn on the AC while on the highway the temperature would remain steady. For some reason after driving in the city for 5 minutes with almost no traffic at all, the temperature suddenly jumped from 165-ish to around 230F with the AC on, once I turned off the AC the temperature dropped back to normal within a minute. So I was wondering have you guys experienced something like this? And could it be that the AC compressor is going bad so it's putting a lot of pressure on the car so that's why it overheats? Or is it a mixture of my somewhat calcium clogged radiator along with the compressor? Let me know what you all think, especially since I found it unusual for the temperature to drop back fairly quickly just after turning the AC off.
A.AlRub

V63

Sounds like a fan clutch Issue? I prefer to swap those with a flex fan for greater dependability.

Big Fins

I'm not a fan of the fan clutches either, but I think that you have other issues going on to have temperature swings like that. I assume you are running a gauge either plugged into the block where the factory sensor went or the where the temperature vacuum control went.

I ran my '69 at 80+ for 2 1/2 hours a few weeks ago and it never went over the 180o mark, even when I arrived in town and did a little stop and go with it to get home. I have the factory 3 row copper and brass radiator and had the A/C running the whole trip. And the fan clutch is new as is the coolant.
Current:
1976 Eldorado Convertible in Crystal Blue FireMist with white interior and top. (Misty Blue)
1969 Fleetwood Brougham in Chalice Gold FireMist with matching interior and top. (The Old Man) SOLD!

Past and much missed:
1977 Brougham de Elegance
1976 Eldorado Convertible
1972 Fleetwood Brougham
1971 Sedan de Ville
1970 de Ville Convertible
1969 Sedan de Ville
1959 Sedan deVille

wrefakis


"Cadillac Kid" Greg Surfas 15364

First of all there is NO 160 degree thermostat built for your Cadillac.  Cadillac T'stats are special in that there is a bypass in the cooling system that allows coolant to circulate when the main function of the thermostat is still closed. Then, at 185 or 195(Cad stat temps) the main stat opens and when it does so it closes the bypass.
If you are using the "Chevrolet" style 160 degree stat there is no bypass closure, so when the stat opens at 160 degrees the bypass remains open and shorts circuits the cooling system and the radiator.
Your 472 engine was designed to operate at 195 to 210 degrees under normal conditions, and will see 220-230 a lot in South Texas summertime.
The two pictures show the difference between the thermostats.
As far as the interconnection with the AC system there is of course a thermal load placed on the cooling system when the AC is in operation.  Air goes over the condenser first picking up the heat before it gets to the engine cooling radiator, but I would first install the correct thermostat and see what happens.  All newbys (to the 472/500) are taken back by the operating temperatures, but these motors were designed and do run warm and in doing so are ore thermally efficient.
Greg Surfas
P.S. Thanks for the pictures Geoff



    Posts: 5183
    The most valuable antique is an old friend.
    CLC Number: 4719
    Name: G. Newcombe

Re: 1972 CdV 472 ci Running Hot
« Reply #4 on: April 08, 2020, 06:27:01 PM »

    Quote

Sounds OK to me.  Those engines originally came with 195 degree thermostats, the optional, and only other one available, in a CORRECT thermostat is a 185.  The correct 185 or 195 should look like the first pic. below, other GM thermostats may fit but are not proper for the Cadillac 501 series engines (472, 500, 425).  Pic. #2 will fit but is not correct.

* 472-500 thermostat.jpg (15.12 kB, 330x330 - viewed 11 times.)

* thermostat.jpg (9.44 kB, 200x200 - viewed 159 times.)
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

Big Fins

Not that I have pictures as proof, but the 180o stat I put in the '69 is a real Cadillac thermostat. The by-pass block off is the first thing that I looked for when it got here.

A 160, I wouldn't even use on one of these engines. They like heat and plenty of it.
Current:
1976 Eldorado Convertible in Crystal Blue FireMist with white interior and top. (Misty Blue)
1969 Fleetwood Brougham in Chalice Gold FireMist with matching interior and top. (The Old Man) SOLD!

Past and much missed:
1977 Brougham de Elegance
1976 Eldorado Convertible
1972 Fleetwood Brougham
1971 Sedan de Ville
1970 de Ville Convertible
1969 Sedan de Ville
1959 Sedan deVille

35-709

Right, those engines are designed to run warm.  The compressor/AC is not making your engine overheat, at least not directly, it does put an extra load on the cooling system but a properly functioning system is designed to handle it.  If your compressor was 'going bad" it would tell you in other ways than making the engine overheat.   You have a problem in your cooling system, put the correct thermostat in there and get the radiator flushed/rodded out and take it from there.  A lower temperature thermostat will not correct a cooling system problem.  These engines came from the factory with 195 degree thermostats, a 185 degree stat is available in the correct Cadillac configuration already shown above.  A Cadillac knowledgeable mechanic would know that.
Geoff N. 
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

TJ Hopland

John Deere had some series if equipment that used the same stat with that same bypass valve so my guess is if there are or were any made at lower temps that would have been where they came from.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

James Landi

You've received great advice regarding all these concerns --- I write you only to URGE you to get your radiator de-scaled immediately by someone sufficiently experienced to do this work expertly --- and have your engine's cooling system flushed. THe scale seriously impedes the radiator's ability to dissipate not only the engine's heat, but as stated previously,  the extra heat generated by the a/c's condenser  .     James

Bob Hoffmann CLC#96

Guys,
I'd had lots of cars. I've never!! seen a temperature drop like that.
BTW.. all 1970 Cadillacs had a flex fan.
Bob
1968 Eldorado slick top ,white/red interior
2015 Holden Ute HSV Maloo red/black interior.
             
Too much fun is more than you can have.

Scot Minesinger

I have owned three 1970 Cadillacs at one time and the other posts are accurate. 

How do you know that your Cadillac suffers these temperature fluctuations?  If it is hot enough to run ac, it is unlikely that the Cadillac could run at 160'F with the stat wide open and not short circuiting, as it would be hotter, like 190'F or so.  Do you think your gauge is accurate?

Anyway, as Greg wrote start with installing the correct 195'F thermostat.  Check your radiator fan, it should not have a clutch, but rather be a flex fan.  Get the radiator at 100% capacity.  make sure you have good water flow.  make sure your "snorkel" damper at the air intake is not drawing in air over the exhaust manifold reserved exclusively for warm up.  Make sure timing is correct.  Make sure there are no vacuum leaks.  Be sure that the fan shroud is intact.  Now you should be in much shape.

Enjoy your Cadillac!
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

Bob Hoffmann CLC#96

#11
So Scot... my post isn't  accurate?? I said that all 70's had flex fans & my years of experience.  I don't think the flex fan info  has to be repeated . This strange temp. drop can not happen that fast whether someone has a 70 Cadillac or a 65 Chevy.
Bob
1968 Eldorado slick top ,white/red interior
2015 Holden Ute HSV Maloo red/black interior.
             
Too much fun is more than you can have.

Cape Cod Fleetwood

FWIW, the correct thermostat # is AC Delco 12T18E
There are 2 kinds of cars in the world, Cadillac and everything else....

The Present -1970 Fleetwood Brougham

The Past -
1996 Deville Concours
1987 Sedan De Ville "Commonwealth Edition"
1981 Coupe De Ville (8-6-4)
1976 Sedan De Ville
1975 Sedan De Ville

The Daily Driver and work slave -
2008 GMC Acadia SLT *options/all

V63

#13
Since Cadillac was using an idiot light in those years, an after market gauge is being used?
Where is the bulb reading from?
is it properly submersed in water? (is water level full?)
Is the water pump drive belt snug enough? (Slipping?)
Your Rapid temperature fluctuations seem suspect as others have pointed out.,

Maybe of interest.

I had a 2009 DTS that I bought with 70k miles and it always ran about 60-70% hot In warmer months. .  Sometimes on a long grade up to 75%. Typically at highway speeds like road trips.

Over the years I tried everything  up to 150k miles. Tstats, coolants, radiator, water pump, always the same 🙄🤯.

UNTIL, I had road debris puncture my condenser and since it was august hot,  I just fixed the damaged tube with a pinch of epoxy and recharged the AC with a 'replacement'  refridgerant and instantly the car engine temperature maxed out at 50%. Problem finally resolved!

The AC always worked great and equivalence to other DTS I owned, but now (With replacement refrigerant) it's blowing about freezing (32F) at the vents (much better than original 134) 

It was probably 'over charged' when I bought it and since it still blew to factory specs...I never checked it, nor suspected the AC  as the culprit  🤷🏽‍♂️ 

To relate to your situation yes,
the air conditioner can add enough load (especially using a different refrigerant, or over charge)  that increases operating pressures and resulting engine load.



V63

#14
Quote from: Bob Hoffmann CLC#96 on December 16, 2021, 10:06:25 PM
Guys,
I'd had lots of cars. I've never!! seen a temperature drop like that.
BTW.. all 1970 Cadillacs had a flex fan.
Bob

My memory not the best and too many Cadillacs...  err huh...didn't I have 1970 Eldorado's with fan clutches?

Scot Minesinger

Bob Hoffman,

I wrote "the other posts are accurate", meaning everyone who advised on the original question was correct.  Sorry that this was not clear.

In any event, the temperature and operations of the original poster did not make sense, and so I question the accuracy of the temperature gauge.  Since 1970 Cadillacs did not include temperature gauges even as a factory option, who knows how that was added, and if it was even done properly.  I figured that the Cadillac must be in reasonable shape since the ac works, which is usually the first thing to not work in a nice 1970 Cadillac.

Puzzling?

On other Cadillac, I have heard different possibilities, formed my own opinion after seeing pictures, and then when the car gets in my shop the issue is something else entirely.  Hope we find out.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

Eric DeVirgilis CLC# 8621

I have never heard of water temp dropping from 230 to 165 in a minute. And 165 seems awfully low to begin with. That gauge sounds flakey to me.
A Cadillac Motorcar is a Possession for which there is no Acceptable Substitute

cadillacmike68

Clean out or re-core or replace the radiator FIRST, Put in a correct 180 TStat, and then check it all again.

These these cars will get too hot in slowed traffic, especially in congested urban areas, but not this time of the year. Even down here in FL, my 1968 DVC won't run hot, even in Miami. but in the summer - different story.
Regards,
"Cadillac" Mike