1968 overheating problems

[mikanystrom]

So I have had this persistent problem with my "good" 1968 Eldorado (the "rough one" is still for sale, by the way! $3,000 on craigslist Los Angeles, some tire kickers have poked at it...) and am eager to get to the bottom of it.  Reading between the lines of what other people have been saying about these cars, I am gathering that my issues are not that far off from what others have seen.

My 1968 Eldorado had 48,000 miles on it when I bought it a year and a half ago.  I have put 3,000 miles on it since then, and about 1,000 miles in a single week right before Thanksgiving: Los Angeles to Las Vegas and back and then up to San Jose.

The 1968 cars have a temperature gauge.  It has four divisions.  My car has a standard (180?F) thermostat, and when warming up fairly quickly gets up to about "1/5" (just below the 1/4 mark).  On a cold day and driving slowly on the open road it stays nailed there, just like a modern car.  On a hot day, in traffic, going uphill, or whatnot, it goes higher.

My problem is that I get pinging from the engine when the temperature runs off---at altitudes below 1500 feet.  On the way to Vegas and back I was watching the temperature gauge (which would basically tell me which way the road was sloping: high temp means uphill, low temp means downhill).  No pinging at altitude or with the temp at "1/5", but when I get down to L.A., it pings at part throttle.

So retard the timing, you say?  Well the vacuum advance is set to a bit less than factory at this point (I set it to factory settings and have since backed off), centrifugal should be OK (car actually doesn't ping at full throttle and high RPM so ..), base timing is retarded to 3 BTDC (spec is 5.5 BTDC).  What I need is less vacuum advance.

But if I reduce the vacuum advance, the car overheats!  In fact, even as it is, it will overheat in hot weather (I drove in 95F weather with a/c turned on last summer and it was boiling over every time I stopped).   I have an aux. electrical fan covering a small part of the passenger side of the radiator, it's connected to the a/c compressor clutch circuit, so it was running all these times (I leave the a/c in AUTO, 70F, most of the time).

More background: I have replaced the timing set (the nylon was totally gone) with a new Cloyes, have a Comp Camps 268H camshaft, carefully degreed in, with new lifters and pushrods, pushrod clearance checked.  I know what a retarded camshaft feels like, and that's not the problem.

Vacuum is good, 20'' at idle.  Yes I have searched for all vacuum leaks.  The turkey baster is sealed with RTV all around, and I have the rubber gaskets installed at the front and back of the engine.

High-volume water pump from the place in Santa Barbara (Flowkooler I think). 

I was discussing the issue with a VERY helpful gentleman named Jim at US Radiator in L.A. (I recommend!) and he suggested that I take some temperature readings, so I did.  Test conditions are:

California Central Valley I-5, mostly flat road.  Ambient was about 65F, speed 80-85 mph.  I stopped at a gas station and took some readings as quickly as possible with the engine idling.

"Cold" tank 88C = 190F
"Hot" tank 108C = 226F
Hot hose (rubber surface) 90C = 194F
Low hose (rubber surface) 78C = 172F
Transmission lines 104C/101C = 219F/214F

Jim said that the cooling from my radiator looks good because the drop is 36F (or Rankine to get technical) from hot to cold tank.  I think I actually cleaned it once by filling it with muriatic acid in my bathtub in an attempt to get at this problem.  But the incoming water is too hot.  He suggested trying a 160 degree thermostat, but I don't think that will work---simply because the thermostat has got to be open all the way at this point (I think my temp gauge was around "1/2" when I took these readings, thermostat is open at 1/5...)  So I would be inclined to think... maybe a better radiator is in order?  US Radiator has nice looking ones, but they are 800 dollars.  "Ah well...the price of owning a Cadillac"?

But.. then I noticed something.  The car has a dual stainless exhaust I got from a company that specializes in old car exhausts.  It runs "as stock" up to the muffler: stock on a '68 Eldorado is a dual system from engine to a transverse muffler above the rear axle and then a single resonator on the passenger side by the fuel tank.  I just have dual resonators, that's the only thing that is different.  I have had the heat riser flapper REMOVED.

Still, my intake manifold is getting hot.  And I mean HOT.  The last three images I attach are of the intake.  I see readings up to 208C (406F!), see my third-from-last attachment: this is looking at the base of the carb from the driver's side.  The object right above the hot cursor is the kickdown switch and the dark thing on the right is the air cleaner snorkel.  The second-to-last attachment is an illustrative view from the passenger side.  Exhaust manifold at around 280C (562F) but the intake is 184C (363F)!  The last attachment is pointed at the choke coil (pass. side manifold near carb base).

Any ideas out there?  Is such a hot intake expected?  At the same time, my radiator always looked a bit wimpy to me... forgot to measure how thick the core is but it's not much...

[V63]

A lean fuel mixture is probably at issue. This will cause all your symptoms. Could be incorrect carburetor, adjustments or jetting ...to worn cam lobes

[cadillacmike68]

I have similar issues with my 1968.  More later I have to go look at it. Supposedly they have repaired the speedo cable that they FUBAR'd when re-installing the engine.

[mikanystrom]

Lean primaries, you mean?  Hmmmmmmm... then it should be OK at idle.  I wonder if it is.  It's in the transmission shop now so I can't really check that.

Worn cam lobes is unlikely---yes I could have messed it up when I broke it in (the cam is basically new, before my drive the other week it only had a few hundred miles on it), but the car runs like a bat out of Hell, so that's really unlikely, I think.

Idle mixture is set for zero lean drop.

Ignition advance is normally connected to manifold vacuum.

Tune-up procedure is:

Disconnect vacuum advance.  Increase idle to 550 with idle screw.  Set base timing.

Connect vacuum again.  Reduce idle to ~650 (I really can't get it to idle right at 550 on manifold vacuum, it gets really sensitive, on ported vacuum it will).  Fiddle mixture screws for zero rpm lean drop on both sides. 

The car is in the transmission shop but sure when I get it back I can try bigger primary jets.  The bigger cam could certainly cause it to run lean....

V63, would you suggest trying to install an oxygen sensor?  Any other way to verify it's running lean?

["Cadillac Kid" Greg Surfas 15364]

Mika,
This subject has been discussed on this and other Cadillac forums something like 13 and one half billion, gadzillion times, and I am sure you will get a lot of suggestions, but here goes the short form;
The Cadillac 472/500 series of motors was specifically designed to run at a higher thermal efficiency than the other motors of the day./  To do that it is necessary to keep the heat in the motor so that incoming charge has a little help in getting to the something like 1100 degrees (F) that combustion temperatures run.  That said, any oit was only something like 8.5:1igh compression 472/500 motor when putting out power such as climbing a hill or high speed highway will run anywhere from 100 to 230 degrees F.  If you de-tune these motors you can get the temperature down, but in top tune those are the numbers.
Now, vacuum advance is very important for both fuel efficiency and temperature control. without the correct vacuum advance connected to the proper vacuum source temperatures at idle in traffic can quickly climb [past 230 degrees, that's why they have the thermal vacuum switch on the motor to allow full vacuum under high motor temperatures.Also, at cruise vacuum advance is required to provide additional advance to maintain correct combustion and motor temperature.
IF you have the proper vacuum advance can the correct timing mark on the damper and pointer and the proper advance curve in your distributor and you are using "good" gas(I know I had a real hard time keeping my '72 eldo from pinging on 91 octane "California" gas and it was only something like 8.5:1) and it still pings I would suspect hot spots in the cylinder heads.
I would start by verifying your timing mark is correct by bringing the #1  pioston to TDC visually through the plug hole or with some sort of device inserted through the plug hole to let you know when you are at TDC,  and then checking the timing mark to be sure it agrees.
That's where I would start.
Greg Suerfas

[V63]

If your car has a clutch fan...that’s the first thing I changed out (to OEM flex fan) on my 68. I’m in AZ and drove it all summer , with COLD AC, 120+ Degree ambient temps . No temperature problems or pinging. I did add pertronix, but be SURE to epoxy magnets in or they fall out of dist rotor ring.

[cadillacmike68]

1968 were all clutch fan, but I just changed mine to a 1970s ElDorado 7 blade no clutch fan.

Too lean on the idle screws or too little advance will make it run hotter. At idle the advance is all vacuum, so that has to be right. You can get a crane Cams adjustable vacuum advance. I need to adjust mine because it Still heats up at idle in traffic, even after a new re-core of the radiator and the changed fan.

[WTL]

All I can say is, I am considering water/methanol injection in the new year to combat the overheating/timing retard/pinging Hobson's choice that these motors present the modern driver with pump gas.  I don't know if that will help, but it's an idea. 

[cadillacmike68]

You guys out in CA are SOL on fuel, but at least here I can mix a couple gallons of 110 octane to get rid of any pinging or knocking.

["Cadillac Kid" Greg Surfas 15364]

Back in the mid to late 60's (when your car was built Mika) the oil companies were engaged in the "Octane Wars".  I remember 114 Octane being advertised. I remember being able to run my 12.5:1 L88 motor on "pump gas".
Greg Surfas

[mikanystrom]

Thanks all for your input... I am well aware this topic has been discussed many many times, but... I'm trying to make some progress on one specific car here and all that's been said, well maybe something is relevant to my case, but I'm not sure what.

Maybe relevant: I also have a 1970 De Ville that seems to run OK, it is touchy, yes, but I have managed to get it not to ping or boil over.  It has almost the same engine and I run it on the same gas.  In fact in all the years I have had that car I have never not managed to get it right (after some tweaking and going back and forth, indeed...), with slightly retarded timing and not too much vacuum advance.  It doesn't even boil when it's 100F outside (although it does sometimes stall at idle when it gets really really hot, something with the carb I think).

On the '68 that's having problems: My timing mark is in the right place.  I just replaced the camshaft a few months ago, so I have gone over that part of the engine with a degree wheel back and forth and back and forth... TDC feeler, protractor, micrometer, etc etc etc. 

Yes ignition is Pertronix.  Yes I have Crane Cams adjustable advance, with the adjustable stop as well.  I set it by the book to start with and then went a bit less aggressive on the advance because it was pinging bad at part throttle.  Yes the vacuum source is always the strong one (I bypassed the thermal valve so it's ALWAYS on manifold vacuum, I did this to cool it down a bit!)  It's really not so bad now, but...the ping comes back once the temp goes over 1/5 (or altitude goes below 1,500 ft).  And car still boils over when it's hot out.

So my real question is, how do I get the '68 to run as well as my '70?  IS it normal for my intake manifold to be at 406 F?  A '70 doesn't do that, or does it?  (My '70 is ALSO in the shop...)  Does the '70 have heat riser passages in the manifold?  Can they be blocked off?  Can that help?  Or is that just a wild goose chase?

It seems to me that if I could just keep the engine at "1/5 TEMP" all would be fine, and that means more cooling capacity.  Or a richer mixture?  Or do something about that hot manifold?

Yes I have a new clutch on my clutch fan.  You think the flex fans are better?  Yes the '70 has a flex fan.  I could search for one of those...

["Cadillac Kid" Greg Surfas 15364]

Mika,
Just a little follow up.  I picked up my 73 (high performance motor) from the transmission shop yesterday and was driving home. In order to get the car to idle I have a vacuum advance that starts at about 4 inches of vacuum and is full inat around 10. In order to be sure I don't detonate under full throttle I have a three way solenoid that vents the vacuum to the advance for racing. I was cruising on the freeway at a bit over 70, and the temperature had stabilized at 185 degrees F.  I switched the vacuum advance off, and within 3 or four minutes the temperature had climbed to 215 degrees.  When I switched the vacuum back in it went right back down.
Coincidence?
I think not.
Greg Surfas

[walt chomosh #23510]

Mika,
  Fundamentals,fundamentals,fundamentals. Vacumn advance MUST work properly.(for motor to perform properly) Cooling fan must be spaced and working as designed. (My son put a US made flex-a-lite fan in his 5.0 Mustang and it blew the over pressure valve going down the highway 6 times or so!....a small electric fan was added and problem solved)  A lean mixture WILL overheat a motor EVERY time!.....hope this helps. Cooling systems are simple BUT can cause headaches when something is not quite right.(please report your fix when found)....walt...tulsa,ok         

[Jeff Rosansky CLC #28373]

Just something to point out. We all check the engine for vacuum leaks. But may I suggest checking your brake booster. A few months ago mine was running horribly and the temp light came on for the first time. I just took it home and parked it the next morning I started it and could barely keep it running. I went to move it and the brake pedal was hard as a rock. Long story even longer, the plastic checkvalve on the booster had cracked.
Jeff

[35-709]

One thing about the thermostat that you mentioned in your first post, there are only 2 correct thermostats for the engine you have, the factory installed thermostat is a 195.  You can get a 185 and those are the only two thermostats that are available for the 472/500.  A 160 will fit but will not work properly, the "501" series engine (472/500/425) thermostat is of a different design.  I have pictured one below.

These cooling systems worked just fine when new and in proper condition should now also.  Has the radiator been removed and cleaned --- professionally?  You might need to block off the exhaust passage where it enters the intake manifold on the heat riser valve side which means removing the intake manifold.   

[dplotkin]

Gentlemen, I submit to you that while most of you are correct in everything you write, take it from a guy with a lot of various old cars; overheating is almost just about always either lack of air flow or lack of coolant flow. Blaming it on the engine should be last. The Rad needs to be flow tested, the block needs to be flushed and checked that the jackets aren't munged up. The water pump belt needs to be tight and the impeller intact. The lower hose cannot be collapsing.

Any time I hear people say "they tend to run hot" I know a load of BS is nearby. Cars with cooling system deficiencies tend to run hot. Cadillac built no such car. An engine so mis-timed that it overheated would run too poorly to have time to overheat. An engine overheating from too lean a mixture would have burned out a few exhaust valves first and run too poorly to have time to overheat.

All these things are possible, don't get excited. But they are not likely. Water flow and air flow, look there first.

Dan

[cadillacmike68]

One thing about the thermostat that you mentioned in your first post, there are only 2 correct thermostats for the engine you have, the factory installed thermostat is a 195.  You can get a 185 and those are the only two thermostats that are available for the 472/500.  A 160 will fit but will not work properly, the "501" series engine (472/500/425) thermostat is of a different design.  I have pictured one below.

These cooling systems worked just fine when new and in proper condition should now also.  Has the radiator been removed and cleaned --- professionally?  You might need to block off the exhaust passage where it enters the intake manifold on the heat riser valve side which means removing the intake manifold. 

The "501 series engine is a different design from what? From the 472/500? A little clarification please.

[35-709]

The "501" series engine is the 472/500/425.  The thermostat for the 501 series engines is a different design than other GM engines.

[cadillacmike68]

OK, I knew that. You can't put a chevy thermo in these blocks.

When my 1968 is not stuck in traffic, it stays right around the 1/4 mark, which is what the owners manual states. These past few days it doesn't even get up that far unless I'm stopped. Of course I'm driving with the top down and the Climate Control OFF. If it gets really cold, I turn it to Auto and about 78 and it warms the front seat area right up (and sucks gas out the wazoo!).