Am I overheating?

[mtnjag]

Hi Paul,

Good example of confusing IR readings but they do seem a little extreme. I may be in error but i would think the bypass hose temp should be hotter then the bottom return hose from the rad? Perhaps because it’s larger it reads hotter.

If you can touch the tanks and header tank and leave your hand on it i think your coolant is well below 100.

Your fan draws temp down 10 degrees and turns off. Again not looking back bit if you leave it on does it draw it down further?

Still think you should put the DVOM probe in the coolant flow from the outflow hose at the thermostat temp sensor. You can watch the thermostat function and get an actual temp.

Road test will be the best if you can trust it not to overheat. My car runs cooler the faster it goes. Dont be fooled at 25mph, air flow is low. Fan should go off and car should run around thermostat temp cruising at 40mph+ or so depending on ambient temp.

Have fun. (Maybe have a chase car)

[Philk]

One quick question...... have you checked whether the fan relay is working properly? If you bridge the two connectors to the otter switch with the ignition switched on, the fan should operate. If you remove the bridge, the fan should stop immediately (this is how a fan override switch works). If the fan does not stop then you have a relay/wiring issue. You can do this test from cold without the engine needing to run.

[paulsco]

Hi Layne,

Thanks for your suggestions; I will have another check tomorrow.

Hi Phil,

The fan works and comes on when the otter switch is shorted and when the engine gets hot, the problem is it does not go off when the fan cools the radiator. The temperatures are still to be determined.

There was no relay originally on the 4.2, so I have fitted one to the fan in the vain hope that it would take the pressure off the otter switch. The fan works with or without the relay, it just doesn’t go off and I am fairly convinced that the temperature is low enough in the header tank for it to do so.

Maybe yet another faulty otter??

Paul

[PeterCrespin]

If we were to believe the temp readings as described, the bottom outlet hose is 12-15C hotter than the top left inlet hose (the top right doesn't really flow into the rad although it is connected).

You appear to have invented the internal combustion radiator. I should get yourself down to the patent office PDQ :-) Either that or the 80-ish is a typo and it should be 60-ish, which would make sense with 68/65 inlet temps?

If the lowest pressure cap doesn't puke coolant, keep working with that until everything is finally sorted and then run with the highest one for insurance if you intend using the AC condenser on the front.

[Doug Buchan]

Hi Paul,

Thanks for your reply.

I have checked that the fan is pulling through the radiator into the engine bay.

As for the pump; I rebuilt it when I was building the engine, but it is not impossible that it has a problem.
There are no strange noises though and it is turning ok so nothing internal would appear to have become detached.

Hello Paul,
Are you using the original timing cover or did your rebuild require a replacement?
I ask because it's a regular practice to fit a later cover with the larger involute if the original is corroded.
Your '65 would be equipped with a 2-3/4" impeller and the later variant requires a 3"

Regards,
Doug

[paulsco]

Hi Doug,

Both my timing cover and water pump are original, although the pump has been rebuilt.


I just thought I would update you all on the progress so far.

As I have established that my car does not appear to be overheating, but the fan is failing to go off, I thought I would delve more into the otter switches.

I have an old original otter switch, but the lucar connection has broken off at the base. I had tried to solder on a new connector, but there was not enough of the old one exposed to make a good connection.
I took it apart to see if I could remove the old part of the connector and fit a new one. It is sealed in, so this was not an option. I decided to drill into the face around the connector and expose enough of the old connector to make a reasonable solder joint and soldered on a new lucar connector.

I thought I would test the temperatures of all five otter switches that I now have.

I heated up a pan of water and used my circuit tester and a food probe temperature tester.

The original otter mentioned above went on at 89C and off at 86C. The book says it should be 80/72.

Replacement otter from one of the usuals was on all the time.

The second otter from one of the usuals was 91/80.

First Mitsubishi 91/88.

Second Mitsubishi doesn’t come on, even over 100C.

I fitted the original otter to try it out as it is the only one so far I haven’t installed and from the gauge at 90C the fan came on and went off at about 87C.

The inferred temperatures were all over the place.

The bypass hose remained hot throughout.

I think this will do for now; it is not overheating and the fan is coming on and going off. I will make a further judgement on the road.

There has been a lot of discussion on JL about 4.2 header tanks and their plumbing.

The internal pipe that runs from the left to the right has a hole in it where the otter switch pokes through to pick up the temperature; the hole is not sealed by the switch, so hot water from the pipe can escape into the header tank and therefore into the top left hose to the radiator therefore bypassing the core.

The header tank remained fairly hot and I have concluded that although the original otter and the Mitsubishi had a similar cut off point, the Mitsubishi would not block the hole in the through pipe nearly as well as the original, so may require a slightly lower heat level to go off.

I am far from an expert in these things and perhaps I do not understand it fully, but two things strike me;

The bypass is not restricting the flow sufficiently when the thermostat is open even though it is the one with a sleeve and hot water is flowing to the left side of the radiator, bypassing the core and secondly the 4.2 header tank with its extra left hand hose to the top of the radiator also bypasses the core.

In my case the temperature in the header tank, despite the core being just warm is too hot for the otter switch to go off with all but the original otter.










Regards,

Paul

[mtnjag]

You ever put a manual switch on it?
I have one and use it when going into slow and go conditions, coming off a spirited drive to a slow 1 mile crawl on a little road into my house, etc. Comes in handy and lets you keep from going into the upper end of where you want to be. Rather than getting to the garage at the top end, you get there at the bottom of running temp.

[PeterCrespin]

“The bypass is not restricting the flow sufficiently when the thermostat is open even though it is the one with a sleeve and hot water is flowing to the left side of the radiator, bypassing the core and secondly the 4.2 header tank with its extra left hand hose to the top of the radiator also bypasses the core.

In my case the temperature in the header tank, despite the core being just warm is too hot for the otter switch to go off with all but the original otter.”

1) You’re mixing up left and right, Paul.

2) Whilst there is somewhat of a connection at the added top right 4.2 hose, there is no major flow (or should not be) into the body of the expansion tank or from the body of the tank into the right upper radiator tank.

3) Acting as a header, the tank serves as the high point in the system, ensuring the heat-shedding engine and radiator are always brim full of coolant.

4) Acting as an expansion/contraction reservoir, the tank has to permit ‘leakage’ around the switch, into/out of the pipe running through that carries the main flow.

5) The core of your new alloy rad will always feel much cooler than the tanks because the skin burns quicker against a solid smooth suface by conduction, than it does by radiation across an air gap and secondary fin contact. This is not an issue at all.

6) Having the correct type of sleeve thermostat and having a correctly-operating bypass closure are, unfortunately not the same thing. It’s not a great system but better than nothing. By 1968 they’d abandoned it for the modern spring-loaded foot type. Hence once everything is up to temp the bypass hose is always going to be warm even with low flow.

The important parameters are does the temp keep climbing at idle or in slow traffic? No. When the fan kicks in does the temp fall fairly quickly? Yes. Your system is fine. Stick the high pressure AC-type cap on provided it’s the right length and enjoy the car. If nothing else, the switch business proves that sometimes the word new stands for never ever worked...!
5)

[paulsco]

“You’re mixing up left and right, Paul”.

Yes; sorry about that

Thanks for your comments Peter; good explanation and very reassuring.

Paul