MKI / MKII S type 240 340 & Daimler 1955 - 1967

1967 Mark 2 running hot

Old 07-11-2019, 03:35 AM
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Default 1967 Mark 2 running hot

I own a Mark 2 , 1967 3.4 Jaguar which is running hot

I have changed the thermostat, coolant and added water wetter to the rad, I have also added lead addative to the fuel and it runs just above the 90 degrees on the thermometer - any suggestions?

Old 07-11-2019, 05:51 AM
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Presuming that the radiator is not clogged, water pump OK, system properly bled, correct tune ~ not over lean & timing correct.

Have you fitted the correct thermostat with shroud that covers the bypass slot when open & ensures that 100% of coolant goes through the radiator fully warmed up?

Old 07-11-2019, 09:26 AM
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Firstly I would buy an infra-red type of hand held temperature gauge and obtain a number of readings around the engine.

This will provide you with a comparison to your dash mounted temperature gauge. It will also inform you of any major hot spots on the engine. Trying to chase down a problem without some certified data is a fool’s errand. You will find a hand held temperature reader very useful and far cheaper than a seized engine repair.

If any odd hot spots are found then you will have something substantial, (not faulty gauge readings etc), to proceed with and to make sensible assessments. For instance you may find that the cylinder block area around No 2 cylinder on the exhaust side is showing signs of overheating. In that instance you might decide to remove the core plugs and attempt to clean out silt in the block. Having said that, it is harder to remove silt than one might believe and dosing with citric acid followed by clean water flushing and then with washing up liquid solution may help. An engine can be run locally for a few days with citric acid in the cooling system, in fact this acid is very successful in cleaning at higher temperatures.
Old 07-11-2019, 10:44 AM
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I agree with Norman regarding a fouled or scaled block which is why I listed some presumptions. Cleanliness of the block being another example.

A word of warning with IR thermometers. Read the instructions well. They have their limitations & can be misleading in the hands of those not accustomed to using them & can lead you astray.

A good Fluke or whatever digital contact thermometer can sometimes be a better guide in automotive use.

IR Thermometers become more useful in steel plants & the like where you can't get close to a concaster etc. due to radiant heat.

That said IR thermometers can be good go ~ no go devices correctly adjusted.

Whatever, it is a very good idea to check that your temp gauge is somewhat accurate.

Last edited by Glyn M Ruck; 07-11-2019 at 11:21 AM.
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