1972 LeSabre overheating

[Pete Phillips]

I am at my wit's end. The '72 LeSabre convertible that I have been trying to sell and finally got a deposit on, has suddenly decided to overheat every time I take it out on the highway. After 4-5 miles of highway driving, the hot light glows slightly. I pull over, open the hood, and the upper radiator hose is so hot that I cannot touch it for long. Same way with the radiator, from top to bottom--no change, way too hot . In the 19 years I"ve taken care of the car, it has never had an overheating problem. I had planned to drive it to the new owner in Massachusetts this week and next, but those plans are now out the window and my one-way airline ticket home is a waste of $600.

Here is what I have done in the past 10 days: flushed and drained cooling system; replaced thermostat with a new 180-degree unit; replaced radiator TWICE with new ones. First replacement was not as thick as the original, which showed a little bit of scale inside, but not bad; new one overheated so I spent $450 yesterday and got a three-core, heavy-duty radiator and installed it. No change. New water pump today, including having to drill out two broken bolts, so a 2-hour job became a 10-hour job in the 100-degree heat. Fan clutch operates properly; 7-blade fan pulls lots of air through the radiator --you can put your hand down behind the radiator and feel the wind when it is running. Fan shroud is in place. Most of the radiator and heater hoses are new. I do not suspect a leaking head gasket because there is no oil in the coolant; no coolant in the motor oil; no smoke or steam out the exhaust. and engine runs well. I am flat-ass done. I have no idea what more to do and am ready to take the car back to the old lady who owns it and let her find someone else to deal with it. I probably have 40 hours of uncompensated time in this, not to mention nearly $1000 in parts. Aren't old cars fun?????

 

Pete Phillips, BCA #7338

Leonard, TX

[rocketraider]

Pete, do these engines have an exhaust heat riser flap? Possibly stuck closed? Maybe other exhaust restriction? If it has a ThermAC aircleaner make sure the snorkel flap is opening after warmup.

 

How about ignition timing and vacuum advance operation? Spark plug heat range? Super-lean fuel mixture due to ethanol gasoline? Can you get non-ethanol?

 

All the radiator seals in place? Lower radiator hose collapsing?

 

Then there's the weather conditions y'all are having down there. 100° for days on end isn't doing anything any favors.

 

And it could be this Burick just doesn't want to leave Texas!🙂

[Pete Phillips]

Glenn,

Good suggestions, thanks. Some I had not thought of (ignition timing, etc.) Lower hose is staying open. Air cleaner flap is staying open. Will check other suggestions.

Pete

[avgwarhawk]

My guess is the vacuum advance has failed..

[JohnD1956]

I'd suggest a broken vacuum hose somewhere. Make sure the auxiliary vacuum tank is not broken or compromised. If equiped with a firewall vacuum management portal make sure that hasn't delaminated and is now leaking. 

[old-tank]

Actual temperature?  IR heat gun at thermostat housing?

[JohnD1956]

Does the 350 have the Thermo Vacuum Switch? Its in the intake manifold on the 455, drivers side front. If so it may be malfunctioning and can be bypassed by running a vacuum line from the carb port directly to the vacuum advance on the distributor. 

The thing is that is supposed to switch from ported vacuum to manifold vacuum if the engine temp gets too hot which should speed up the idle. I dont know which port on the carb to run directly. I think it would make sense to use the manifold vacuum line in. 

 

But it may also be the fan clutch. I wonder if it isnt engaging when the air flow temp increases? 

[Wayne R]

Couple of things here…sorry over in Europe  for 3 weeks back today…just in case this helps,best way to check fan clutch at approx 73 degrees  cold engine. Spin the fan clutch as fast as you can by hand….realize it’s hard to do  behind shroud….but you should not  get more than about one full turn….example if it spins about 2 ..3 times then that’s a sure sign it’s on its last legs..also when driving just as engines starts to get warmed up in hot weather, you will notice a noticeable difference in noise from your fan clutch if working properly ..a slight roar noise.

Also.  When you did all the flushing. And refilled did you turn heater in the on position and made sure you elimated all the air in your heater hoses. Etc…regards.

Edited August 17, 2023 by Wayne R (see edit history)

[EmTee]

I would perform a compression check just for peace of mind.

[Frank DuVal]

15 hours ago, Pete Phillips said:

I pull over, open the hood, and the upper radiator hose is so hot that I cannot touch it for long.

This is normal. Hose should be ~200°F+ in Texas.    Get an IR temperature gun and get real data, like old-tank says. You can also use it to scan across the radiator core.

 

Is the water (coolant) boiling? See steam escaping from the overflow/vent/plastic tank?

 

15 hours ago, Pete Phillips said:

the hot light glows slightly.

An IR gun will tell you if the temperature sender is reporting a hot condition or is just failing internally. The fact that it glows slightly seems odd, it is a snap switch* that should be on or off. Ground the wire with the key on and see if the lamp lights bright.

 

* Internal spring makes it be either open or closed once the actuator (the heat part) moves past a preset point inside.

Edited August 17, 2023 by Frank DuVal (see edit history)

[Pete Phillips]

John D, I think you are on to something. Vacuum hoses have been changed around when we put a new intake manifold on the car last spring. I cannot find a vacuum hose diagram in the shop manual. Does anyone have access to one?

Pete Phillips

[Pete Phillips]

Is the water (coolant) boiling? See steam escaping from the overflow/vent/plastic tank?

 

Not boiling over; no steam escaping.

[rocketraider]

2 hours ago, Pete Phillips said:

I cannot find a vacuum hose diagram in the shop manual. Does anyone have access to one?

By early 70s those are usually in a separate emissions section or under engine tuneup.

 

Distributor Thermal Vacuum Switch:

Ports should be marked D (distributor vac advance canister), M (intake manifold vacuum source) and C (ported spark vacuum source from carburetor). It switches vacuum advance from ported (above throttle plates) to full manifold vacuum at 220° or so  coolant temp to advance timing and hopefully cool the engine.

 

Frank may be on to something with light operation. Is it possible someone in this car's past installed a gage sending unit instead of warning lamp?

[NTX5467]

Is there supposed to be a deflector under the core support to help make air go through the radiator, on the bottom of the core support?  A flap on the bottom of the hood that might be missing, over the core support area?

 

Call the airline and get your ticket converted to a "TRAVEL VOUCHER", good for about a year.  That used to be possible, so worth a try now.

 

NTX5467

[JohnD1956]

1972 4N series vacuum routing

[JohnD1956]

 

Assuming it has cruise control too

 

[JohnD1956]

These two schematics indicate a source for the heater and ac units. Note, they show you may have the vacuum manifold or the vacuum storage tank hooked directly to the back of a 4bbl carb.

 

[rocketraider]

That TCS switch in JohnD's diagram can complicate things. It's designed to prevent vacuum advance to the distributor until the transmission is in high gear and it's not above suspicion. If it fails it won't allow vacuum advance under any conditions.

 

Didn't make any sense to me in the 70s and still doesn't. There won't be any vacuum advance under hard acceleration in lower gears, so why put in a failure-prone component that does nothing but complicate things. It made the E P A happy I guess.

[NTX5467]

That thing was not on everything back then, but some applications, as I recall.  Most of them got unhooked sooner or later., or vac hosed "around", running the vac advance from the carb itself.

[Pete Phillips]

I think we fixed it. Ignition timing was off by nearly 20 degrees and temperature sending unit was faulty. Could have been a vacuum hose problem, too. We found and fixed so many things that I've lost track. They all know me on a first-name-basis at the local auto parts store!  Thanks to all for the suggestions and diagrams that I couldn't find in my shop manual.

Pete Phillips

[JohnD1956]

18 hours ago, rocketraider said:

That TCS switch in JohnD's diagram can complicate things. It's designed to prevent vacuum advance to the distributor until the transmission is in high gear and it's not above suspicion. If it fails it won't allow vacuum advance under any conditions.

 

Didn't make any sense to me in the 70s and still doesn't. There won't be any vacuum advance under hard acceleration in lower gears, so why put in a failure-prone component that does nothing but complicate things. It made the E P A happy I guess.

This is an interesting comment.  I went back to read the section on how that combined switch is supposed to help. The immediate part standing out is that the engines in 72 Buicks are designed to have no vacuum advance at low engine speeds.  So this switch which is both the Transmission Controled Vacuum Spark Advance control (TCS in the manual) and a thermo vacuum switch (tvs) has two different functions. The TCS blocks ported vacuum at low engine speeds while the tvs allows manifold vacuum to advance the timing  if the engine temp gets to 220 °. 

 

[60s GM Fan]

Congrats on the sale and fixing the heating issue.  I know the 67 will run 190-200 when its 110 outside but I've been told thats normal lol.

[pfloro]

20 hours ago, rocketraider said:

Didn't make any sense to me in the 70s and still doesn't. There won't be any vacuum advance under hard acceleration in lower gears, so why put in a failure-prone component that does nothing but complicate things. It made the E P A happy I guess.

 

I'm not 100% sure, but I believe the purpose of TCS was to reduce the amount of NOx under acceleration.  At least in 1970, my father's '70 Pontiac Lemans (350-2V) had a pressure switch mounted on the side of the THM350 which was only closed in 3rd gear.

It controlled a vacuum solenoid which was between the vacuum advance unit and manifold vacuum.  I don't think the carb had a ported vacuum connection.  I suspect that by only having mechanical spark advance in 1st & 2nd, combustion efficiency was reduced,

peak flame temperature was lowered, and therefore NOx was reduced.  I pretty sure this engine didn't have a TVS...

 

I'm guessing that as the requirement to reduce emissions in the 1970s increased, a TVS replaced the vacuum solenoid.  ???

 

***

 

FYI:  My 1973 Plymouth Duster (225 Slant Six - Torqueflite)  had a 2 port vacuum switch mounted in the cowl opening.  Similar to the 1970 GM system on my father's Pontiac, it was connected between the vacuum advance unit and a ported vacuum source on the carb.

According to the shop manual, it prevented vacuum advance for about 20 seconds every time the throttle was opened from the idle position.  The vacuum switch also was temperature sensitive and allowed advance whenever the ambient temperature was

below a certain threshold.  This engine did have EGR...

 

As much as I don't like the complexity of today's computer controlled engine management systems, I don't miss all the primitive "hang on" vacuum emission controls of yesteryear. 

 

Paul

 

 

 

 

Edited August 18, 2023 by pfloro (see edit history)

[NTX5467]

Problem is that the more efficient you make the combustion process, decreasing HC and CO, the "heat of combustion" rises and NOx production is increased.  So ignition timing "tricks" and less mechanical advance at lower rpm levels (and initial timing, too) helped address those things in order to get them past the IM240 test each year.  Allegedly, above 2500 rpm or so, all of the ignitioni timing functions were supposed to be close to what they used to be, before emissions.

 

In about the 1973-74 time frame, there were some publications which had instructions of how to re-tune the engines for best results.  That was when it was discovered that most any '72 Olds Cutlass 350 4bbl COULD average 20+mpg on road trips.  Back when the normal Interstate speed limit was 70mph.

 

NTX5467

[60FlatTop]

Early this week I went over a friend's '51 Studebaker with my trusty IR thermometer. He said he thought it was running hot. I almost got the camera out, should have. It was textbook at every point. I shot it right on the thermostat, in and out of the radiator, down the water jackets, and even looked at each exhaust port exit to confirm they were uniform. Great little tool. I have a Greenlee.

 

Somewhere around 20 years ago my '64 Riviera started lighting up HOT shortly after starting. I tie wrapped a yest gauge to the high side refrigerant line to  get a reading. I still open the hood and take a peek at it. Probably should put the right sensor in the replace the bad one. Well, when I feel like mopping up a little coolant I will.

[avgwarhawk]

Glad the running hot is resolved.  20 degrees is quite off.  How is she running power wise with the adjustment?

 

I cut my teeth with points, dwell and timing on a 73 Estate Wagon.  Turning the hex screw to the points  under the distributor cap and listening to the 455 purr made me understand all work in unison as designed when adjustments are where they need to be.  That 9 passenger Porche 455-4 came to life. Baltimore to Washington DC in 30 minutes is the testament. That's a story for another day. 

[NTX5467]

Somewhere I read the points adjustment procedure was:  "Insert Allen wrench into the hex on the points.  With the engine running at hot base idle, turn Allen wrench left until engine misfires.  Note position.  Turn Allen wrench to the right until engine misfires.  Note position.  Turn Allen wrench 1/2 way to the lh direction misfire location.  Set ignition timing."

 

That's from the days when a dwell/tach was a very sophisticated piece of test equipment, as was a timing light.

 

NTX5467

[rocketraider]

In the day, it was.

 

Neighborhood garage was able to make most repairs; tuneup, brakes, fluid changes and the like. But they did tuneup the old fashioned way, with feeler gauges or in a few cases a matchbook cover.

 

Around 1966 one of their parts jobbers brought a Dixco dwell tach and timing light out there one day and the owner's teenage son fell in love with it. The dad and uncle wanted nothing to do with it but the boy saved his birthday money and pay till he could afford it. He took to it quickly and was good with it.

 

All of a sudden that little country garage was turning out "scientific" tuneup and tuneup business doubled wanting young Charles to work magic. But dad and uncle never learned to use it. 

[rocketraider]

Pete, since things have been corrected and tuned, is this LeSabre running like a cat whose backside has been scoured with a corncob and turpentine?🙀

[Frank DuVal]

Hey Pete, side question.

 

Did your 1970 three speed manual have a switch mounted on it so the shift levers would depress it only in third gear? That is the TCS switch. My 1970 Estate Wagon three on the tree had it when I bought it. It was removed, along with the TCS control solenoid in the intake manifold when I learned what it did.  Wires got in the way while changing the clutch disc. Which I did a lot, caused by loaning the car to people who knew how to drive a stick, but not a 455 cu in engine trying to move a 4500 pound car with a stick! Car was built for economy, not hills.