Talk Morgan Forums Talk Morgan Members Section Special Information Diagnosing an Overheating '68 4/4

June 9, 2019, Ottawa, Canada, 30C(86F) outside. Wanna-be mechanic here. I have my Dads '68 4/4 a long way from home.

Unfortunately I happily drove 400km with the thermostat reading 70C --- the ambient temp outside was only 5C but eventually suspicious I checked the coolant to find that the reservoir was empty. I hadn't checked it before I embarked on this trek (sorry everyone) - topped it up for the last leg of the drive, into the city, and now the temp gauge is reading 110C. I reached my destination, checked that coolant was at the top of the radiator cap and then I noticed a pin hole leak at the top of the rad (in the top reservoir part).

The aluminum Marston Excelsior radiator had sprung a pinhole leak before or after I stated the trek and (coincidentally?) the engine is now overheating into the ~110-115(230-240F) degree Celsius range (according to the temp gauge and an infrared thermometer on the top of the rad). I can fix the leak but in the meantime I want to diagnose the overheating. I don't think the pinhole leak in the rad is my problem (or is it?).

The water pump visually looks good. No leaking.
I removed the thermostat for the second test run and also tested it to find that that it operated normally in a test bath.

I've removed (to find the hole), flushed and refilled the rad, and am not losing enough coolant from the pin hole in the 30minute test-run time, to get up to temperature, to need or be able to top it up.

First test: after I flushed and refilled the rad with deionized water, I let it idle for 20 minutes (maybe not long enough) and it peaked at 90C. Seemed good enough for a test drive.

Second test: Driving through downtown up to Rideau Hall, 40 minutes, 30C ambient temperature, thermometer goes up to 90C then after 30 minutes-from-cold, up to 110C, back to 100C... I put the heater on when the thermometer got to 100C.

I'm going to seek professional help now but would like to hear if anyone has any ideas.

Thanks,

Brad
'68 4/4
Engine: V-Comp, 116E GT, Ford Cortina
Radiator: Marston Excelsior
Water pump: Lucas 22716N

Have you checked for mayonnaise in the rocker cover or radiator, which might indicate a head gasket failure? Hopefully that’s not the case but for the time you ran with the empty coolant reservoir the temp could have been sky high at the head.
Hope all goes well , cheers John

Things I'd check:

1. Water pump - make sure it's actually working. Remove a hose to see what the flow is (heater hose is good). Take care - the water will be very hot and only do it for a second or two but shutting engine off.

2. Air lock - you may have an airlock in the system that needs bleeding out.

3. Compression test - may show any headgasket problems.

As the temperature went up after it was topped up, I'd suspect an airlock as well.

Thanks, John. No mayonnaise in the rocker cover, rad or oil dipstick. I did drain some oil too because it was overfilled last oil change, and that looked dark but not unusual. I will do a compression test to double check the head gasket.

Brad

Thanks for the suggestions, TBM

1. Water pump check - can I do that with the engine running and cold? That's what I did. There's not a whole lot of pressure or suction but it is flowing. I disconnected where it comes out of the heater first and the flow was less than when I checked the hose going in to the heater. The thermostat has been removed. I made a video recording of the result https://youtu.be/CQTs_J-ky5o

2. Will look into the air lock next.

Thanks again,

Brad

Personally, I think that looks a little weak but the pump is definitely working. It could be an airlock that's causing a depleted flow....

Water pumps are cheap, and an easy replace, so might be worth replacing it.

I did a block test and it showed no combustion gas in the coolant.

Brad

Are you sure the car actually is overheating and it's not just the gauge reading high? Check the gauges are all earthing properly.

Should this thread not be in the Maintenance and Servicing section?
Just a thought...