Overheating thoughts?
 

Hi All,

Just finished a nice sptingtime run down the interstate (about 53 MPH for around 30 miles for part of it) and noticed something I really had not seen before.. My motometer was actually showing a litte red.. Well, it got redder and redder.. When it started getting into the "your engine is hot" range, I started to get a little concerned.. I cracked the Gav open about 1/4 -1/2 turn and noted it started to drop a bit.. I also moved the retard to total full advance as far down as it would go (was up about 2 detents maybe).. It did stay warm, and I noticed that at 48 or so the heat would level out a bit and drop, but running wide open at 53-55 it would start building a bit more heat than it would release..Ambient air temp was about 65 degrees or so..

Some details: Engine has about 600 miles on it, still pretty darn hard to turn over by hand, new water pump, 6 blade fan and running about 60/40 water/antifreeze. Ran very well all winter with hardly ever seeing any temp on the motometer.. Radiator flows very well, is a 10 fin and was just cleaned/degreased a few months ago.. No bubbles in the radiator when running and no steam out the tailpipe or leaks around the head. Standard engine build, no high compression head, but a b cam with hardened valves and seats. Engine timed and points are good, verified with a timing light after the run

Thoughts? Running hot due to newness of motor? Running the carb to lean?

Let me know what you think gang!

- Dave

Re: Overheating thoughts?
 

I think you hit it on the head right there, not yet broken in.

What where the recommmendations from the builder on the break in of the engine?

Re: Overheating thoughts?
 

Are you using a thermostat. If not, I would install one. That fixed my coolant loss at highway speeds of 45 to 55 MPH. If it was my engine I'd have more miles on it before going that fast that far. Maybe you just pushed the coolant out the overflow.

Re: Overheating thoughts?
 

Nine times out of ten overheating means a radiator problem. You say yours is clean and degreased. Did you take the tanks off and rod out the core? If not, that's where I'd start. No other cleaning method will give you a really clean radiator core.

Re: Overheating thoughts?
 

That's very true. There is a flow test published that fails to take into account the quanity of water needed to properly cool the engine.

Let me explain. If you block off the bottom of the radiator, fill it up and then remove the blockage and you see that the water stops after 3 secs do you have a good radiator?

The answer is maybe. Did you put in a quart of water or a gallon of water?

Re: Overheating thoughts?
 

Running it a bit hard for a new rebuild I would say.

Re: Overheating thoughts?
 

I think motometers are really neat looking, but I wouldn't drive without a
thermometer hanging down from the gage cluster. You can tell instantly
when you are getting the least low on coolant. At least that has been my
experience. JMHO

Jack

Re: Overheating thoughts?
 

Get your radiator recored .Flow test are BS.

Re: Overheating thoughts?
 

Re: Overheating thoughts?
 

I had an overheating problem. Had my radiator professionally done, re-installed it, filled with pure water, for the test run. I went about 50 miles on a hot day with some hard pulls. No problem, no leaks. When I came home I refilled it with 50/50 antifreeze and water (or maybe stronger) since I live where theres cold winters. Went back out and boiled all the coolant out on the first hill. I cut the mix down to about 20% antifreeze and have had no problem since, about a year. I think the pure antifreeze didn't cool in the non-pressurized system.

Re: Overheating thoughts?
 

Hi All.. Thanks for the feedback.. I have an extension spring on my motometer to try to sniff the coolant temp vs "steam" or air temp above the coolant.. I don't run a thermostat myself. I'll pull the motometer out and log with a hot water source "real water temp vs readings" to see if I can get an idea what the difference is between "red" and "really red" :)

In a well running and well cooled engine, can anyone share with me the temp differential between the upper input and the lower output on a good radiator?

Do you get a 30-40 degree difference between the top and bottom?

I have an IR laser temp meter I'll pack along to see what the upper to lower differential is on the radiator once heated up well as well as the side to side across the tubes to see if there is any differential side to side which might indicate a plugged condition. The radiator served the car very well before the motor rebuild, but that does not mean it is also a 100% efficient unit either :)

I'll keep a log and share what I learn.

- Dave

Re: Overheating thoughts?
 

No real recommendations.. Avoid extended high speed for long runs, etc for 1st 500 or so miles, vary the speeds, don't wind it up or lug excessivley.. I am running a full flow filter that the rebuilder put on for me, so I am going to change the oil (1st time) and filter this week, as It's likely about as long as it should be for the break in.. Also running ZDDP zinc additive in the oil as well during at least the first 1500 miles.

Re: Overheating thoughts?
 

Dave,
You asked about temperature differential between radiator inlet and outlet. Here is a long answer to your question. I did a bunch of testing of that awhile back and concluded that due to other variables it doesn't mean much. For example: With a thermostat that is just partially open, flow rate will be quite low. In that situation, since the water is moving slowly, its temperature will increase a lot while flowing through the engine, and will likewise drop a lot while flowing through the radiator because it's in there for a relatively long time. With an open thermostat (or none) water flow is fast, so there is less time for gaining or losing heat. The temperature differential through the engine and through the radiator will be much less. That doesn't mean that less heat is being transferred. The total BTUs being being dissipated by the radiator may be about the same. If each gallon flowing through the radiator gives up just half as much heat, but there are twice as many gallons flowing through, the total amount of heat being dissipated will be about the same. With warm air, high flow rate, and low engine load (not much heat being generated), the temp differential might be as little as 5 degrees. With cool air, low flow rate, high load, the temp differential can be many many times greater. All this is not to say that there is no point in measuring those temperatures. Just keep in mind the other variables and that there is no single "should be" temperature differential.

Bob

Re: Overheating thoughts?
 

I had overheating problems on 2 As.I tried all the fixes.Nothing worked but new radiators

Re: Overheating thoughts?
 

A poorly cooling radiator will cool at slow speeds, but not at high speeds. Its probably being aggravated by the tight engine. The poor cooling could be due to clogged tubes in the core, or loose fins. Without some means of restricting the flow like a thermostat, or as is the case in some re core jobs, a missing baffle, the pump can over pump the radiator and push the coolant out. That is especially the case with a poor flow, as the coolant cannot get down below the top tank before its over filled by the pump. The more clogged the core, the quicker the car over heats. Your radiator is probably marginal, so it cools fine when the weather is cool and at low speeds. Once the engine is broken in, it might stay below the over heat range, but a good radiator should be able to cool even a tight engine on a warm day. Ultimately, you are looking at having it rodded out or replaced at some time in the future.

Re: Overheating thoughts?
 

Did you run the old motor at 53 mph? I'm betting on the radiator. I think a few too many squirts of water pump grease can plug things up pretty quickly.

Steve

Re: Overheating thoughts?
 

LOL.. The old motor wouldn't pull the car along in 3rd gear it was so wore out, and 2nd gear would lose power on a 1% grade. I'm also thinking that since the engine was bored out .80 over, it will have thinner cyl walls and not as much iron to work as a heat sink.. I'm going to try dropping the coolant to 20/80 (was 50/50 as i drove it all winter in below zero conditions at times) and see if the 'thinner' mix works better for summer.. Worse case is that I'll have the radiator rebuilt.. Have rebuilt just about everything else on the old girl :)

Re: Overheating thoughts?
 

Could always go to a distilled water test. Did you back flush the block when you installed it from the rebuilder? The top of the block is a wonderful place for all kinds of debris to accumulate. Even blowing out the block with air won't get some of that radiator plugging stuff out. Bob

Re: Overheating thoughts?
 

It always strikes me as unusual that someone would pay good money for a new engine, then cut corners on something as essential as rodding out or replacing the radiator at the same time. Its sort of like rebuilding the top end of the engine and neglecting new bearings because they are expensive. I know, many people do it. But think of how easily and quickly you can ruin your new engine if it over heats. Model A blocks do not like overheating. They crack easily. Think of the entire engine and all its components as a system, not isolated and independent components. Your rebuilt engine is incomplete without re conditioning the cooling system.