1955 Engine & Trans Temps

[Paul Falabella]

I have noticed that if I drive less than about twenty miles the needle will stay a little below the "N" on the temp guage. If I go more than about 20 miles the temp gauge creeps up to, or just a tad past the "N". Never higher and no sign of overheating, even on a hot day with A/C on, even stop and go. I also noticed that while the transmission remains full, the fluid(Castrol Dex/Merc) looks to have thinned out on the dip stick. After sitting and cooling it goes back to thicker, darker red. All the while performance is fine.

Just want to know if any or all of this is normal?

Thanks,

Paul

[NTX5467]

If you have a non-contact IR heat "gun", you can check the temps in both cases at:  thermostat housing, radiator upper hose attachment, radiator lower hose attachment, then the upper, middle, and lower sections of the radiator's core.  With that data, you might be able to see if when the gauge temp rises, just how much and such.

 

I once had a "creeping heat" issue on my '77 Camaro, even with a 3-core Modine radiator.  The car came with a factory flex fan, which I considered a "+", but I came to suspect that as it flattened out at highway speed, the air coming through the radiator was being blocked rather than just flowing on through (as it might with a fan clutch that was free-wheeling at that speed and lower temp.  A new flex fan didn't change anything, but a fan clutch conversion did.  Later, I discovered that although the core looked good from the top, it was about 1/3 clogged on the bottom side . . . much heavier when I took it out.  Replacing it with a composite OEM production ACDelco "upgrade" radiator, it was like putting an ice truck in front of the car.

 

Mine never got significantly past the 210 degrees mark, but it did concern me as it never ran past "just below" the 210 mid-mark on the gauge.

​

​ATF is about the same as 10W motor oil, or thinner.  The main thing I'd worry about on that is that the trans if "Full" when hot, regardless of which brand of fluid you have.

​

It might well be that the radiator is becoming more inefficient with mileage.  Be sure the fins are clean (with air or higher pressure water) and that the fan is moving the air as it should.

 

Keep us posted on how things progress.

 

NTX5467

[KAD36]

Mine is about the same Paul, and the radiator core is new as of about 12 years ago and clean. Would consider them normal. 

 

With a 160 thermostat the gauge rarely got to the N - sat between the C and N at the start of the arc'd "band" on the gauge. With a 180 in there which is been used for the past 20 years it will stay a little below the N and sit dead square on the N on highway speeds.  After a highway run if I'm sitting in traffic it will creep up to the edge of the "band" between N and H (on the Roadmaster/Super type temp gauges).  Then when moving it comes right back down.  What thermostat is in yours?

 

While keeping up with JohnD on the way to South Bend it stayed right around N to a little above and our "express" team was moving at a pretty good clip.  When stopped and turned off at a rest area, it would just about peg to the H.  Right on startup it would settle back down to N.  It was somewhere in the high 80s outside and pretty humid on that drive if I remember right.

 

So, after all that gauge activity, it never overheated, never spit out the overflow tube, just kept on truckin.  My hunch is the N is about 180 and anywhere 1/4 range below to 1/4 above is just fine - thats after my 30+ years of driving this car and watching the gauges behavior.  On a few rare occasions in over 100 deg heat in stop and go traffic its sat pretty close to the H, but there were no issues. In fact I can remember once it was running right at the H and it eventually also settled back down.  Purely weather and condition related.

 

Trans temp - couldn't tell you.  I have dex 3 in there and it does get thin.  I have a new cooler on there - NOS - put it on with the rebuild.  In examining the coolers design surface area (its a fluid to fluid heat exchanger vs a fluid to air) it appears barely adequate to do a good job of exchanging heat given the "slip" nature of a dynaflow at startup and how much heat the fluid probably absorbs. If the fluid doesn't smell burnt or is brown, doesnt have metal in it when wiped on a clean cloth and keeps a pink to reddish color, its fine.  I've seen the fluid burnt (not mine) and with metal in them and you can tell something is wrong.  Old Tank has a well designed aftermarket auxilliary cooler tucked up inside the frame of his car with a fan on it if you're interested in adding one.

 

When I first started driving this car I used to drive myself crazy with the gauges.  My dad told me I was nuts and to get in the car and drive the darn thing.  He was right as usual.

 

NTX has a good idea on the IR sensor - that will help you "visualize" the gauge calibration and satisfy your curiosity.  Consider taking it after a highway drive then after alot of stop and go driving.  Be interesting to see what the water temps are going to and coming from the trans cooler.

 

My observation is that the particular temp gauge in our cars is for general indication only and it would surprise me if this particular style of non numerical gauge tracked consistently after 60 years let alone when they were new.  On mine theres about 25-30 degrees of  rise from the N to the H and maybe 20 degrees from the N to midway between the C and N.

 

The oil pressure gauge is another one of those "is it too low" topics because its general indication, but thats a different thread.

 

Drive it and keep having fun.  Your car is looking great.

Edited August 24, 2015 by KAD36 (see edit history)

[buick5563]

It all sounds normal, and I bet it is usually hotter here. Good idea to check and verify. Check top tank to bottom of tank to make sure it's cooling. Remember, the gauge is in the back of the engine so it is usually lower than the thermostat housing.

[JohnD1956]

I thought the temp gauge in the rear of the engine, made for a hotter reading on the gauge.  The theory being less air flow from the fan.

[NTX5467]

If the temp sensor is in the rear of the motor, I would suspect it would read a little hotter on older and more high-mileage engines.  Why?  The rear of the motor is lower than the front and that's where the cooling system sediment will settle out with time and miles.  In that scenerio, being back there would alert the driver to something that's getting ready to happen, just not in the next 100 miles or so.

 

The first GM car with a trans temp gauge was the '84 Corvette.  I drove one when they were new and paid attention to the trans temp vs. engine temp.  As we all know, the engine temp will come up fairly quick, but it took a good 10 miles of driving to get the trans temp up to engine temp.

 

Our former service manager had a brother that did parts for a large construction company.  At one job, they started having failed automatic transmissions (Allisons, possibly).  For the concrete trucks to get to their delivery point, they had a long descent to that point, in reverse.  Later, we had a customer who pulled a travel trailer who brought in their C20 for service . . . it had a contact-style trans temp sensor.  So, our service manager took it out for a diagnostic drive and watched the trans temp gauge.  Torqueing the engine against the foot brake did raise the temp a little, but not nearly as much as when he did a closed-throttle "over-run"/coast down situation from about 40mph in manual low gear.  THAT's when the trans temp significantly elevated.  Why?  When the engine is trying to slow the vehicle (working against momentum AND gravity, the oil in the torque converter is running into itself, which is building heat in the fluid, as the vehicle is slowed by an engine that wants to idle as the transmission won't let it (until it's good and ready), until the engine and vehicle speeds are more matched to each other.

 

I concur with KAD36 on the fluid.  If it's not darkened and/or has "stuff floating in it", has enough fluid to efficiently move the vehicle on the coldest day of the year (when it might be a little bit below the "ADD" line, some have a little dimple for the 32 degrees F "cold" fluid level), then everything's probably as good as it's going to get.

 

Personally, I'm happy if the "hot" fluid level is just a bit below the "FULL" mark, so there's a little additional expansion room should some really hot weather or difficult driving situation might be encountered.

 

Enjoy!

NTX5467

[Paul Falabella]

That is what I expected. The transmission "warms" up and moves the Temp needle farther, well after the engine temp has topped. My main concern was the thinned tranny fluid, which is apparently normal. My concern was that I had never seen this on Hydramatics, Powerflights and the like.

I will however refrain from downshifting on long downgrades, which should not be a problem since there is nothing higher than 100ft. ASL for 80 miles around here!

Thanks for the info

[old-tank]

All oil and fluids will thin out at higher temps.  One of my 55's has marginal transmission pump pressures (when hot) and it is that one that I added a fan driven transmission cooler and added STP to the fluid (a stop-gap that I did 10 years ago).

The back of the cylinder head is the coolest  and if you look at the circulation you will see why:  cooler water from the bottom of the radiator-->lower hose-->lower engine block-->back of the cylinder head-->across the cylinder head-->water manifold-->thermostat--> upper hose-->radiator.

Most of the temperature gauges on these cars are pegged out hot at only 200*F (and are still pegged hot at much higher temps).  If you want to see hot then drive down here and watch the gauge when stuck in traffic after a high speed run (outside temps in the mid 100's).

Willie

[Aaron65]

I've determined that my '53 Special's gauge, when in the exact middle, is 180-185* according to my infrared thermometer at the thermostat housing.  Of course, it starts to heat creep after about 30-45 minutes of 60-65 mph driving.  It makes it up to about 3/4 way up the normal band (which is pretty small on a '53).  This equates to roughly 195*-205*.  Back when I ran a 160* thermostat in it, it would barely get above halfway, so it would run 180*-185*.  

 

Of course, coming down into a traffic situation after this put it into the top of the normal band pretty quickly either way, and it would usually stay there.  That's 215*-220*.  My shop manual said that low speed driving on warm days may send the water temperature up to 212* or so, which is about what I'm seeing.  My engine has been hot tanked and has a newer radiator core, but there was still a lot of stuff floating around in the cooling system after the rebuild, so I had it flushed.  It's probably due for another flush now.  

 

Just my experiences...

[Airy Cat]

On a hot day {90*} my '55 will run around 195*

[avgwarhawk]

All oil and fluids will thin out at higher temps.  One of my 55's has marginal transmission pump pressures (when hot) and it is that one that I added a fan driven transmission cooler and added STP to the fluid (a stop-gap that I did 10 years ago).

The back of the cylinder head is the coolest  and if you look at the circulation you will see why:  cooler water from the bottom of the radiator-->lower hose-->lower engine block-->back of the cylinder head-->across the cylinder head-->water manifold-->thermostat--> upper hose-->radiator.

Most of the temperature gauges on these cars are pegged out hot at only 200*F (and are still pegged hot at much higher temps).  If you want to see hot then drive down here and watch the gauge when stuck in traffic after a high speed run (outside temps in the mid 100's).

Willie

 

 

Willie is Gospel when it comes to 55's.   Go with what he says!   

[Joseph P. Indusi]

Just to add to this post, my 53 Special with Dynaflow and power steering, runs around 180-185 F at the thermostat outlet on an average summer day with a laser pointer temperature gun.  Using the same gun on the bottom of the Dyanflow oil pan, I read 155 to 160 F.  The Dynaflow cooler gets coolant from a nipple on the water pump and returns to another nipple near the first one.  The coolant going to the Dyanflow cooler comes from the bottom of the radiator tank.  The temperature difference between the top tank and the bottom tank is about 25 F.  it is very important to route these coolant hoses correctly to assure that the Dynaflow cooler operates properly.  I use this car in several summer parades so I have a 6 blade fan from a 1950's Cadillac with AC on it.  The faster I go with this car the cooler it runs.  The radiator has been re-cored a few years ago. 

I think the ethanol in the gasoline contributes to these cars running hotter than they did back in the day.

Joe  

[Aaron65]

Just to add to this post, my 53 Special with Dynaflow and power steering, runs around 180-185 F at the thermostat outlet on an average summer day with a laser pointer temperature gun.  Using the same gun on the bottom of the Dyanflow oil pan, I read 155 to 160 F.  The Dynaflow cooler gets coolant from a nipple on the water pump and returns to another nipple near the first one.  The coolant going to the Dyanflow cooler comes from the bottom of the radiator tank.  The temperature difference between the top tank and the bottom tank is about 25 F.  it is very important to route these coolant hoses correctly to assure that the Dynaflow cooler operates properly.  I use this car in several summer parades so I have a 6 blade fan from a 1950's Cadillac with AC on it.  The faster I go with this car the cooler it runs.  The radiator has been re-cored a few years ago. 

I think the ethanol in the gasoline contributes to these cars running hotter than they did back in the day.

Joe  

 

Joe, what do you run for a thermostat in your Special?

[Joseph P. Indusi]

I run a heavy duty 160 F thermostat that I got from Bob's Automobilia. The opening is larger than on some of the cheaper brands I have seen. I will look to see what the brand is; comes in a yellow and blue box.

Joe

[Aaron65]

I run a heavy duty 160 F thermostat that I got from Bob's Automobilia. The opening is larger than on some of the cheaper brands I have seen. I will look to see what the brand is; comes in a yellow and blue box.

Joe

 

I liked running a 160* thermostat in mine, but I found that it gunked up the breather by not getting the oil hot enough.  I'd like to give one of the Bob's thermostats a shot.  Thanks!

[Guest walterpilot]

My '55 was never de-tuned to burn alcohol gas. (10.5 to 1 compression in the 322), so 'crap' corn-gas, even with additives, detonates and overheats the engine. I put Cam 2 Purple 110 octane race gas, or 100LL Avgas, runs like a champ!

BTW, my old 55 Super 4dr Lead Sled, turns the quarter mile from a standing start at 91mph.

Edited September 16, 2015 by walterpilot (see edit history)

[SpecialEducation]

My '55 was never de-tuned to burn alcohol gas. (10.5 to 1 compression in the 322), so 'crap' corn-gas, even with additives, detonates and overheats the engine. I put Cam 2 Purple 110 octane race gas, or 100LL Avgas, runs like a champ!

BTW, my old 55 Super 4dr Lead Sled, turns the quarter mile from a standing start at 91mph.

 

My biggest problem with corn-gas is what it does to the soft parts of the fuel pump!  I do go out of my way to get ethanol-free, but I've never gone so far as to get the leaded blue from the airport.  I've been tempted, but the Special is lower compression than the rest, so I don't know that we'd see $5.45/gallon worth of improvement.

 

For the record, ethanol has less heat energy per gallon and burns cooler than gasoline, but the stoichiometric ratio is very different.  Feeding alcohol to an engine mixed for gas will result in a lean mixture.  If you want to change out your soft parts to materials that alcohol won't eat, your high compression motors would be happier tuned to burn E85.  Just expect your mileage to go in the toilet, because you'll burn about 40% more fuel with a properly tuned E85 setup than you did with straight gasoline.  When the fuel/air mix is correct, ethanol is very detonation resistant.

[old-tank]

My '55 was never de-tuned to burn alcohol gas. (10.5 to 1 compression in the 322), so 'crap' corn-gas, even with additives, detonates and overheats the engine. I put Cam 2 Purple 110 octane race gas, or 100LL Avgas, runs like a champ!

BTW, my old 55 Super 4dr Lead Sled, turns the quarter mile from a standing start at 91mph.

Tell us more about the modifications on your 55.  Stock compression ratio is 9:1 and will run fine on 87 octane e-10.  91 mph quarter would be like low 15's et in a 4500 lb car?  I'm guessing 400 hp and that much or more torque?

[Bhigdog]

Kind of makes me glad I lowered the compression in my cars, including the Vette, when I rebuilt them. I can run 87 octane all day with no complaints from any of my engines and truth be known the lowered performance isn't noticed since I drive my old iron like there's an egg between my foot and the gas pedal................Bob

Edited September 16, 2015 by Bhigdog (see edit history)