running hot solved

[rdssdi]

I have been plagued with hot running for many years. I had the engine out replaced the front cover and water pump (Bean cassette) replaced the cam drive gears and chain due to a clogged oil hole in the front cover and adjusted the valve clearances as well as timing.

The hot running never went away. Recently I again tried to get the car running correctly. I had the carbs rebuilt cleaned out the new (at time of restoration) alloy tank and replaced the distributor wires and plugs. Not related to the cooling issues but I wanted all perfect.

I thought the Smiths temperature gauge might be reading incorrectly. The gauge was calibrated properly as resistors of set value placed inline would move the needle to the calibration marks on the face of the gauge. They are the twin dots at the top middle and end of the sweep. If the gauge was incorrect it was the sender which I also replaced with same results.


I purchased an Autometer gauge and rigged it to function as a test gauge. I ran the engine and noticed the fan would come on when the engine was very hot and turn off shortly thereafter without cooling the engine. I noticed that before and I replaced the temp switch with a new one of lower "ON" temperature. This was the sender that was now not functioning properly.

I then theorized that it was possible that when the fan relay was switched off the collapsing magnetic field would produce a brief high voltage spike. Could this degrade the sender over a short period of time?

I replaced the sender and relay. I used a relay with internal diode protection.

I ran the car and the fan cycles properly. On at 195 off at 185. I assume the temp gauge sender is in a hotter section of the cooling system than the radiator mounting fan sender.

I like the Autometer gauge. It responds rapidly to temperature changes.

As soon as I complete a few small items I will drive the car and monitor engine temperature.

Bob

[Sea Ranch]

Bob, you are a very clear writer and this is a thorough write-up of your work. Nice. And thanks.

Questions: are you saying the temp problem happened after you pulled the front cover?

Also, you didn't mention testing the rad cap to see if it was maintaining pressure. This is, of course, critical as it allows the coolant to stay liquid for much longer (a 10 psi cap should yield boiling point of about 115 degrees C) and do it's job (instead of vapourizing in various hot spots in the system and becoming useless for carrying away heat).

All this I'm sure you know, but just wondering . . .

Looking forward to the test report after driving . . .

Randy

[rdssdi]

The car ran hot before and after pulling the cover. The original water pump had begun leaking so the cover was removed to repair it. I decided to install the Bean cassette pump as I did not wish to have to remove the head and cover in the event of another water pump leak. When the cover was removed we noticed that the timing gears and the chain were worn. A closer examination revealed that a small oil "weep" hole at the bottom of the inner cover was clogged with sealant. The inner cover had a groove worn by the chain.

The solution was the Bean kit. The mechanic who replaced the cam gears, chain and cassette water pump did so without removing the head. I always thought the head had to be removed to replace the pump and / or the front covers. After all that work running hot persisted.

After some time had elapsed and I replaced or rebuilt most everything I decided to use a very experienced mechanic and disassemble and inspect the engine. I pulled the engine out. We removed the head, pan and covers. We found that one cam was timed incorrectly and there was a large amount of carbon build up on the pistons. Very unusual for an engine that ran very little. We addressed those problems as well as setting the valve clearances. I replaced the engine. It still ran hot.

I believe I have now solved the problem. The degrading fan sender was apparently the issue. I surmise the fan "on" temperature progressively got higher as the sender was compromised by the high voltage spikes. I installed an uprated wiring harness when I restored the car which included relays for other functions.. With the new relay and sender all appears normal. But time will tell.

Bob

[billwill]

Bob, you are a very clear writer and this is a thorough write-up of your work. Nice. And thanks.

Questions: are you saying the temp problem happened after you pulled the front cover?

Also, you didn't mention testing the rad cap to see if it was maintaining pressure. This is, of course, critical as it allows the coolant to stay liquid for much longer (a 10 psi cap should yield boiling point of about 115 degrees C) and do it's job (instead of vapourizing in various hot spots in the system and becoming useless for carrying away heat).

All this I'm sure you know, but just wondering . . .

Looking forward to the test report after driving . . .

Randy

I'm fairly sure that if the cooling system is fully filled with no air gaps in it, the cooling system will reach the rad-cap pressure rating at much lower temperatures as the coolant expands, i.e. it is not normally a vapour pressure situation. If it didn't do this we would never get transfer to the coolant recovery bottle without the engine reaching 115 deg C ish., which we would notice. But we do see coolant transfer out and back, hence my deduction.

[rdssdi]

Once the system is sealed and the radiator topped up and the recovery bottle 1/2 to 3/4 full I run the engine. When it is shut down and cools, coolant is drawn into the system replacing the expelled air. I have experienced 1/4 to 1/2 of the recovery bottle reduction in volume.

The Smiths gauge still reads high but I expected that. I was considering using the Autometer gauge but decided to "calibrate" the smiths gauge so it approximates the actual temperature. The gauge is correctly calibrated. When specified resistances are placed inline in lieu of the sender the gauge needle hits the three calibration marks. So I assume the sender is not compatible despite the vendor claims otherwise.

As a side note I came across a Derale electric fan control. It came with a fan I purchased and as I have the fan relay and wiring already in the car I did not require the kit. I looked at the relay included in the kit and saw it had an internal diode such as the one I now use in my Lotus.

I also want to use one in my TVR. I have the diode protected relays on hand but my memory is poor and I forgot to swap out the TVR fan relay. Maybe I should get a diode protected brain. Probably too late.

Bob

[Sea Ranch]

Bob, are you saying that each time you run the car now, the recovery bottle is losing coolant, or just the first time or two? Presumably, you will reach a point where the system has no air, and the coolant recovery bottle's level will rise and fall and rise and fall with the running of the engine, but not require replenishing. I presume you've done the old "park on a very steep hill, nose up" and run the engine with cap off so the air works its way to the highest point and out the filler cap.

Bill, I believe we are not in disagreement. The goal, of course, is not to reach any boiling point, elevated by increased pressure or not. Just that, in a sealed system, the heated coolant causes a pressure increase which in turn provides the helpful condition of an elevated boiling point, which means that under stress, the coolant is less likely to boil, vaporize and thereby become virtually useless as a coolant (very little heat transfer happening between a metal and a gas ).

So then the purpose of a sealed and pressured system is not that the pressurized coolant cools better per se, but rather that it just hangs around longer, and in tougher situations (higher engine temps) and keeps doing it's job to the best of its ability, instead of "checking out" at 100 Celsius.

As for your comment, yes, would be interesting to know at what temperature the cooling system generates 10 psi. Any temp/pressure above that is bled off by the relief valve. Certainly, the evidence shows that 10 psi is reached long before 115 Celsius.

Randy

[rdssdi]

The coolant being drawn into the system from the recovery bottle is accomplished the first or second running cycle. It began with 3/4 of a bottle now it is 1/2 and remains at 1/2.

Bob

[Sea Ranch]

That's great, Bob. And interesting that your factory Smiths temp gauge is still properly calibrated after all these years.

Thanks for the info on the different sender units. Will keep that in mind for mine.

Regards,

Randy

[rgh0]

.......
As for your comment, yes, would be interesting to know at what temperature the cooling system generates 10 psi. Any temp/pressure above that is bled off by the relief valve. Certainly, the evidence shows that 10 psi is reached long before 115 Celsius.

Randy

A full coolant system with no airspace will initially vent into the recovery tank with liquid expansion as it heats up and generates the needed pressure to lift the relief valve on the cap. Once it is up to temperature it stops venting to the catch tank unless the temperature gets to around 115C at some point in the system . The exact temperature depends on the amount of antifreeze present at which point it starts to boil and generate vapor at above 10 psi and will push more fluid out of the system.

Once the engine cools down in both circumstances and if you have a recovery cap then you will draw the coolant back from the catch tank into the system to keep it full for next time. If you have a head gasket leak causing the overheating then gas gets into the system and it will not fully pull back coolant. The next heat cycle results in more coolant being pushed into the catch tank and so on until ultimately it overflows.

cheers
Rohan