57' over heating

**Duke W.** · August 20, 2007, 12:41 PM

Re: 57' over heating

You didn't mention the ambient temperature, but it was not uncommon for cars of that era to overheat in very hot weather, especially in low speed/stop-and-go driving conditions. Also, the Duntov cam engines were considered "racing engines" and not really meant or designed to tolerate extensive idling and low speed operation.

DeWitts makes excellent radiators, but I have no idea what model you used or how it compares to OE in terms of heat transfer characteristics.

The lack of vacuum advance on 270s increases idle and low speed EGT and will contribute to hot running/overheating at idle and low speed compared to a single point distributor with a proper VAC that is matched to the idle vacuum characteristics of the Duntov cam. It will help to run as much initial timing as the engine can tolerate without detonation.

The specs I have on the 270 (but I'm not sure it it applies to all years) are 7 initial and 28@3700 max centrifugal. Limiting the centrifugal to 22 and runing the initial at 12-16 will help, and being as how the advertised CR was only 9.5:1 it will probably tolerate the above without detonation on current unleaded premium unless you have raised the CR. The ideal total idle timing for a Duntov cam engine to yield lowest EGT is in the range of 25-30 degrees, so you can only get there with a properly configured vacuum advance distributor.

That said the best quick fix you can apply is a 15 PSI radiator cap, which will increase the boil over temperature. A 15 psi cap and a 50/50 antifreeze/water mix will yield a boilover temperature of about 265F.

GM was aware of the overheating issues associated with fifties vintage configurations and the later upgrade to a 15 psi cap, aluminum radiator, and big thermo-clutch fan was an excellent solution and solved the SB cooling system issues. The big clutch fan will move a lot more air at low speed than the early fixed fans, but won't consume excess power at high speed.

Use a quality 180 degree thermostat and don't drill holes in it or otherwise mess with it in any way. A 180 thermostat begins to open at about 180 and is full open at about 210-220, so removing it or messing with it will do no good and is just a worthless bubba fix.

Start with a high pressure cap and go forward with the engineering solutions I suggested as required.

Duke

**David B.** · August 20, 2007, 12:45 PM

Re: 57' over heating

Bob,

I would be suspicious of trapped air in the cooling system. It should cool fine, even in stop and go traffic, assuming the shroud is in place, and the distributor timing is right. I have a 'Be-Cool' replacement radiator in mine (also an early build '57) and it handles all conditions, so the DeWitts is not the problem I think. But, I don't use the stock fan blade.

I drilled a small hole in my thermostat (1/8") and it allows completely filling and "burping" of the system when cold. There have been some recent posts on various burping methods various folks prefer. Some said they jack the front of the car or point it uphill during filling. I just squeeze the radiator hose repeatedly to push excess air out until it stops giving up air while filling.

I hope this fixes it. I plan to drive my '57 to Carlisle next weekend (260 mile round trip for me), and I dread any potential problems too. Although, it has never let me down so far.

Dave

**Duke W.** · August 20, 2007, 01:47 PM

Re: 57' over heating

I further noticed that the 270 centrifugal starts at about 600, and the recommended idle speed is 800-850, so if you set the initial at the recommended idle speed it may actually be less than you think because a few of degrees of centrifugal are part of the reading.

This is an easy trap to fall into on some distributors, so you should always verify where the centrifugal starts and make sure you set initial timing below this speed or set total WOT timing by revving the engine to the point where advance stops and set it in the range of 33-38.

Another solution might be to get a higher pitch fan and install it prior to an event that you expect will involve a lot of idling or stop-and-go driving.

Increase the idle speed to 1000 and if it begins to get hot use a little throttle to increase revs to about 1500 when your stopped, which will increase spark advance and fan flow.

Duke

**Robert L.** · August 20, 2007, 02:05 PM

Re: 57' over heating

Duke,

Temps of the day were mid 70's to low 80's. Previous years this event was in the mid 90's. The car performed well then.

The Dewitts radiator is an aluminum ***M. They also have a 15 psi cap for later year cars that will fit my radiator. I have ordered it and will be shipped today.

I will drain the radiator and "burp" the system as Dave suggests. I remember the recent posts on this subject.

Thanks for the advice.

Bob Lemke
MCMLVII

**Robert L.** · August 20, 2007, 02:10 PM

Re: 57' over heating

Dave,

The shroud is in place. Thanks for the reminder on traped air and "burping" the system.

Have a safe and fun trip to Carlisle.

Bob

**Duke W.** · August 20, 2007, 03:03 PM

Re: 57' over heating

Given the cooler temperatures of this year's event something on the engine has likely changed.

You might want to ask Tom about the heat transfer capacity of the radiator, but if it's an aluminum bolt-in replacement for the OE brass unit it probaby has greater heat transfer capacity than the original.

Check your timing (and dwell) as I outlined previously. Point contact or rubbing block wear changes dwell, which changes timing. If dwell increases, timing is retarded.

I've never gone to extensive lengths to "burp" cooling systems like driling holes in thermostats or filling from the outlet port in the manifold. I just fill the cooling system slowly, bounce up and down on the bumper, then start the car when it is "full". After the thermostat opens I add fluid as required until the level stabilizes and check the system after the next few heat cycles to be sure it is at the "full cold" level. I've never run across a system that would not self purge air by following this procedure.

On systems with coolant flow control valves to the heater core, always set the heat on MAX so the core is filled and purged of air, and running the blower at max speed if it begins to heat up will help keep the temperatature under control while the system self purges air.

Duke

**Clem Z.** · August 20, 2007, 03:20 PM

Re: 57' over heating

i always remove the thermostat housing and thermostat and fill till i see the coolant shows up in the thermostat cavity in the intake manifold. i put back the stat and housing and continue filling the rad.

**Mike McKown** · August 20, 2007, 04:23 PM

My first reaction is to ask if

you checked the 7# cap you have on there now. Have you pressure checked it? Maybe it lost a little coolant first through a leaking pressure cap and that started the downward spiral to overheating.

**Jack H.** · August 20, 2007, 06:18 PM

Amen...

Get the rad cap pressure checked first. Also, when the rad cap is off, check the rubber gasket + the adjacent seating area in the radiator. It's not uncommon to have 'curd' trapped there that generates an uneven sealing surface allowing the rad cap to leak pressure.

Plus, bear in mind that some of these older cooling systems were NOT designed to handle the higher pressures of the later era cars. I'd check with DeWitts before putting on a 15 lb rad cap...

Last, when you're in grid lock traffic on a HOT day, you should see your temp guage climbing toward the red zone before you encounter a boil over. The trick to combat the problem is to INCREASE your idle RPM to make the fan work harder and pull more air through the radiator. Even a boost as low as 200 RPM can make the difference between Old Faithful and a sucessful drive!

**Duke W.** · August 20, 2007, 06:26 PM

Re: Amen...

A modern radiator and hoses should easily withstand 15 psi. The one component, if original that might be weak is the heater core, but I think most radiator shops pressure test them to 30 psi, nowadays.

Duke

**Verle R.** · August 21, 2007, 09:33 AM

Re: Amen...

The DeWitts aluminum is a modern design built with modern methods and will easily stand a 15lb cap. I have had that combination for three years.

Verle

**Doug Flaten** · August 21, 2007, 01:49 PM

Re: Amen...

Amen to the Amen. I looked after some industrial engines that had repair costs of several hundred thousand $'s due to cavitation/corrosion of the wet liners in them. Turns out it was traced back to a bad radiator cap on the surge tank. The 3 engines shared were tied into a cooling system that shared a single surge tank. Sometimes the simplest things bite you.

**paul bowers** · August 25, 2007, 03:05 PM

Re: 57' over heating

duke,
would using a 15lb. cap as appoesd to orginal 7lb. put to much pressure on hoses, clamps and or radiator and there fore make something blow?
cause i have simular problems?

**Duke W.** · August 25, 2007, 11:04 PM

Re: 57' over heating

Depends on how old your components are. If they are fairly modern/new a 15 psi cap should cause no harm. I believe radiator shops usually use 30 psi for pressure tests.

Actual system pressure will not reach 15 psi until the temp hits about 265F, and that's the point when you get boilover. With a 7 psi cap boilover is much lower - I don't recall the exact temp, but it's probably somewhere around 230-240, so a 15 psi cap gives you a good amount of extra margin.

Duke

57' over heating

57' over heating

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