VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Seek advice on engine over-heating

My 216 engine maintains normal temperature while being driven but overheats while idling for an extended period (5+ minutes). Engine temp. crept into the 190s. Air temperature was in the mid-50s. Radiator and water pump have been replaced, new fan belt, 160 degree thermostat, non-pressure new cap, system contains fresh anti-freeze/water coolant. When portable electric fan is applied to radiator exterior, temperature cooled. Exterior temperature gun was used to seek hot spots in block/head and no suspect variations found. Advice from the shop is to mount an auxiliary fan on the radiator and, while that seems a logical approach to the problem, I wonder if that just might serve to cover up a weakness that we haven't identified as I feel like the cooling system should function well without an auxiliary fan, including for an extended idle period. All thoughts/advice welcome, thanks, Bob

Sounds about normal to me.

The thermostat merely opens at 160 degrees. The operating temperature should be higher and even 190 when sitting still. The fan wouldn't pulling sufficient flow of air.

I would do the following:

a. Check for too many bugs in the radiator fins or bent fins.

b. Check for radiator flow. Some flues may be stopped up. (Flush out the engine and radiator. Do them separately. Flushing up threw the flues on the radiator and back through the block vis the petcock on the rear of the block.

Remember that the engine will run to 190 or so when idling. As long as it doesn't boil over and loose too much coolant. As long as there is coolant circulating, you won't do much damage to the engine .If it boils over then check for compression leak.

Do not get a helper fan. That's just masking the problem. Nothing more.

As to the symptoms described. I wouldn't worry much.

Best,

Charlie

First off the 1940 tended to run hot in less than ideal conditions. It is normal for the temperatur to creep up a bit during extended idle espedially if you are come from high speed driving. The most common solotion is to install a 1941 radiator which is a direct fit. It has more cooling fins per square inch. It used to be easy to find new 1941 radiators but today even a good clean used one can be hard to find. The other help is to install the larger fan blade used in a 1940 Master 85 cooling also considered for heavy duty cooling. It has 16 3/4 inch long blades VS the 15 3/4" on your present fan plus the blades are wider...part #877279.
The Master 85 used this fan due to having a 3.73 rear axle ration which requires more engine load on hills, etc.

Charlie/Gene, thanks very much for your advice. First, it was helpful to understand that perhaps my view of an overly hot idle was just a bit off base. A little education always helps. That said, I am interested in pursuing some of your ideas, just to have a margin for error on hot Virginia days if I get in a line of slow traffic. Particularly flushing the radiator and the engine water jackets. My radiator is new and works well at speed, no fin issues etc. Interestingly the Filling Station catalogue, where I bought it shows it as a 3 core fitting1940-41 but may not have the true "fins per inch" of the 41. One upgrade option is a 4 core radiator to use with a different engine (v-8) for only $540. So I'm gonna try your other suggestions! Like using a Master 85 16 3/4 diameter fan blade. I had a buddy tell me that he thought the anti-freeze mix might work better with a low pressure radiator cap, lie 4 lbs. Any thoughts on that idea? Thanks.

Here' a Rube Goldberg suggestion: install an oil cooler.

In both of my 1920's trucks, I was worried about overheating, so I plumbed an automatic transmission oil radiator in the line between the oil filter and the return to the engine, thus cooling off the engine oil. This was in addition to flushing the engine and the radiators. I don't have the cash for a new radiator, so I'm hedging my cooling bets.

I mounted the oil radiator under the trucks, just behind the front axle but a little above it so the radiator will get some air flow.

I've been running this configuration for a number of years and although I have no proof that it makes a difference, it makes me feel better and I have not had any boil overs, even when idling in traffic when it is 98 degrees outside.

Below are a couple of photos that show the oil cooler in my '27 one ton truck (Lurch).

The backyard engineer strikes again!

;-) Dean

Thanks Dean....whatever works! My hope is that following up on Charlie and Gene's thoughts to strengthen water cooling will do the necessary, but I'm glad to know of your approach should additional measures be needed. Thanks, Bob

At 50 degrees you should not have heating issues. When was the last time your head was off to check the water jacket inlets, or your block professionally cleaned out as it is in an engine rebuild (freeze plugs removed)? If you don't know then consider the following common problem:

Overheating Issues, I am Stumped

Good luck, Mike

Mike, thanks a million for sharing the attached thread, such a useful discussion from very experienced folks (which I'm not). The whole discussion on cleaning rust out of water jackets and radiator cores made a real impression on me. My car is in a shop now and head has been off for valves/ seats/guides replacement and cleaning within last year and the block was extensively also professionally cleaned out with freeze plugs removed. That said, comments from Charlie and Gene have made me think that perhaps more effort there might be needed (got a lot of feedback from the shop about what a pain it was and how much material came out). However, they tell me water flow through the new radiator and cooling system seems good, with temp rise into 190s only at lengthy idle, while maintaining temp during test drives on road. Also block and head exteriors were scanned with some type of temp gun and no hot spots identified, which I'm told indicates coolant blockages unlikely. Perhaps idle temps in 190s are reasonable but in ambient air temps in the 50s I do worry. Visual inspection of internal radiator also was positive re coolant flow. Perhaps my fan is an issue as idle temp did come down when small electric fan was held to front of radiator....or perhaps 190s at idle is typical? Thanks for the help on thinking about this, Bob

Hi Bob,

Have you tested the temperature gauge, seems pulling it out wouldn't be too much work if you have long arms?

Good luck, Mike

If you have an original style non pressure neck on your radiator, there is no way a cap can seal it,not even a 4 lb cap. I put a heavy duty fan on my 38 Master and that helped control the idle temperature.

One more thing to think about.
Are you using a premixed coolant or mixing your own?
If mixing your own, are you mixing it in a bucket before adding so you know exactly how strong the mix is?
The higher the percentage of glycol, the hotter the engine will run when approaching the limits of the cooling system, as glycol doesn't move heat nearly as efficiently as water does.
We once saw the proof of this with a JD 4020 tractor. Dad used to like to have his coolant mixed really strong (it can get pretty cold up here) and that old 4020 always ran on the edge of the red under full load. We blew a water pump and didn't have any ethylene glycol on the farm that day so we added pure water to get going again. The tractor never lifted the gauge above 1/2 way again until we drained the water and put a mix back in.
Long story short... an engine that shows no issues with a 50/50 mix may lift the gauge notably above the thermostat opening temperature when air flow is reduced with extended idling if a stronger mix like 65/35 or higher is used.

Stovblt, How does one identify an original style non-pressure radiator neck? Ole, thanks for the tip on anti-freeze mix. Thanks, Bob

The first Chevrolet radiator to have a neck designed for a pressure cap was a 1948 and a 4 pound pressure cap came from the factory. After that point all necks were correct for pressure caps.No presssure caps were used on 1949 models and none on 1950 and 1951 with standard transmissions.

The 1939 and prior could not used a pressure cap because the overflow tube was built into the top of the tank and not the neck.

If your 1940 replacement core was designed for a pressure cap you could sAFELY USE A 4 OR 7 POUND CAP.

I could be wrong, but I think the filler neck designed for a pressure cap will have the relatively wide "seat" area about an inch down in the neck and running evenly all the way around the opening. And of course the overflow tube will be just above this "seat" except for 1939 and earlier as pointed out by Gene.
Those designed for non-pressurized caps may have a narrow "shelf" there, but not wide enough for the spring loaded part of the cap to seat properly against. And in the case of my 1946 truck, the inner hole in that "shelf" isn't fully round.
Maybe Gene or someone else could correct me if I'm wrong?

Gene/Ole, thanks for the above on radiator caps and I will follow that up. Now, I think there is a significant piece of information that I have failed to share (age 71 does result in some memory gaps form time to time). In passing along information provided by Gene to the shop where my car is located on the Master 85 larger fan diameter and the need for that in the master due to it having a 3:73 rear, the shop reminded me that they had discovered my rear end has a 3:55 ratio, taller yet from the master 85. I think therein my lie an important source of my idle overheating, at least after having been out for a drive. I guess I should be thankful that it runs down the road within temperature range.....that, I suppose may change during hot summer days. So I guess I'll need pursue all ideas to strengthen cooling capacity. Bob

I'm not sure I understand how the rear axle ratio will affect the cooling at idle. Plus the difference between a 3.73 and 3.55 is only about 5% reduction from an engine speed perspective.

My limited experience is that most of the time the overheating scenario that you are describing is due to curd in the block and head. And as it breaks loose after you add cleaners and flush the system it plugs the radiator. So the "new" radiator is not as effective as you want.

I know this is exactly the situation I have with my '37. I did a lot of work flushing the block in multiple directions and got a lot of curd out of it. And the radiator was tank cleaned and flow tested. Even with all that a hot day here in the Midwest (90 - 95) the temperature will immediately climb to almost 200 at idle. The temperature will immediately drop back to about 180 if I slightly increase the idle speed with the hand throttle or as soon as I start driving.

The 1937-1940 engines tended to run on the hot side. A number of improvments in 1941 eleminated this problem.
On my 1939 I installed an overflow tank - which Chevrolet introduced in 1938 to help solve the burping of coolant when the engine is shut off.
In the olden days it was common to add water every time you got gas - especially in hot weater and after high speed driving.

I agree with Gene, the '37-'40s tend to run slightly hot in town during the summer. My '40 runs at slightly below 180 at extended 65 mph (during summer temps) driving and midway between 180 and the red during stop and go after being on the highway. I have seen it pegged in the red when stopping for gas after running on the interstate. If I let it idle for extended periods of time (during the summer) the temp sets at slightly below 180. I usually don't have any over flow because I keep it serviced to just above the plate or core which leaves plenty of room for expansion. Gene is also right about servicing. I still check the oil and water on the '40 every time I put gas in. Back in the day the good stations used to check the air in your tires too. Today I run my vehicles from servicing to servicing without checking anything unless a light comes on.

Hi Mike and Gene,

Thanks for the confirmation that the temperature rise I see at extended idle in hot weather is probably normal. It has never been cause for concern, just something I keep an eye on.

Like Mike, I do not have an overflow problem. I just keep the core covered with about a 1/3 antifreeze-water mixture.

Is it just the 37 to 40 engines or is it in the design of the vehicles causing the heat issues,my 37 with a 57 235 will sit and idle at 180 all day long.

The 1941 engine had two water circulation holes on the back where is meets up with the block, the1937-1940 had only one. The pump rotor was larger in 1941 and that pump was used righht up into 1954. The 1955 was completely different. The extra large water pump rotor mounted right into a very large opening in the front of the block. In 1955 a new fan with larger blades was used but it turneed slower to reduce fan noise.

Awesome info.
That 2 hole vs 1 hole waterpump backing plate always has me scratching my head. It sure looks like a 1941 up waterpump could be used on a 37-39 with a single hole backing plate? The reason I question this is 1941 up water pumps are very easy to find but the 1937-39-40 pumps are much harder to find.

Attached is a picture of my block that has a single large hole being a December 37 casting. It looks like I could (in theory) open up that one single hole into a huge oval and use a 2 hole waterpump or backplate.

There is also a large plug right below this water pump inlet hole (my engine) or holes (1941 image) that opens right into the water jacket. I can get several fingers inside the single hole in my block all the way down to this large hole that will end up with a plug installed. It sure looks like the block and backing plate could be opened up for way more flow. Not that I plan to, but the single hole could at least be chamfered a bit to direct water flow to the sides of the block.

The biggest difference I see with the 2 hole design is that each hole sends coolant cleanly down the outside of each cylinder and the 1 hole hits the first cylinder and then the coolant has to decide whether to go left or right and I'm sure one side gets considerably more flow than the other.

PS: Yes, my 216 is the correct shade of green. Pontiac green. Not the correct shade of dark grey lol.

The one hole and two hole backing plates are different in size and the attachment holes are different. I think the two hole design came out to direct flow down both sides of the block. That one hole is larger or similar to the area offered by an open thermostat so it shouldn't represent a higher restriction.

Thanks. The mounting hole spacing is all I can figure. I had a couple 2 hole waterpumps but tossed them years ago. Wish I had them to look at.

I had a handful of loose back plates and recall all the holes lined up other than the obvious 2 but don't fully trust my memory. The hole spacing sure LOOKS the same overall.

Edit: seem to now recall Gene pointing out hole spacing to Rusty and I in a thread a while back. Memory kinda works. Sometimes...
Edit 2: Found a pic online where someone overlayed a single hole plate over a double hole block and painted the outline - attached. Height of two holes is likely important for flow to top of block...

That explains why the 37 to 40 water pumps are more expensive then the 41 to 54s