Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing 2008 4/4 temperature issue

Hi all, I’m looking for advice. I own a lovely 200 Morgan 4/4 with a 1.8 duratec engine. Since I’ve owned it I’ve had an issue with the temperature gauge. The car gauge reads 90 degrees for a while but then steadily rises to anywhere between 110-120 when the car is being driven at a constant 3000-3500 revs on the bypass. I’ve checked all over the engine and coolant system with a laser temp reader and all the readings appear normal but the gauge is still showing 110 degrees. I should add that the radiator fan kicks in when the gauge reads 100 and a OBD tester which was used during a run showed the high reading in line with the temperature gauge even though the actual engine temperature tested normal with the laser temp gauge. I’ve also installed a new and tested thermostat which made no difference. I’m now wondering if the engine temperature sensor could be the issue but I’m open to advice.

Could be the voltage stabiliser. See here

Sounds like the sensor as you suggest. The gauge itself is obviously working correctly if the CANBUS reading aligns with the OBD readout.

I did wonder if the sensor is located in the normal Ford Duratec position or some custom MMC one

I had a similar experience earlier this year with my 1986 4/4. After many years of showing a steady 90C under all conditions, it started showing 110-120. At all times the ECU temperature reading was normal and tallied with coolant temperatures taken with an IR thermometer.

I ended up replacing the temperature sensor, thermostat, water pump, and voltage stabiliser. The gauge still shows a higher than normal temperature despite repeated readings which show that the coolant temperature is exactly right.

I've decided to just accept the fact that my temperature gauge now reads high, as if I were to replace it I'd have to replace all my gauges. A single bright shiny new gauge in a dashboard of otherwise shabby nicely patinated 40 year old gauges would look daft, and I can't afford a full set.

Greetings Neil, great choice of car

The 110-120 temp that you are seeing is the cylinder head temp which will be completely different to the thermostat temp at the bottom of the engine. Your temp sensor is located at the top of the engine at rear of the head. There is only one temp sensor and it is shared by both the ECU and MFU. Your OBD tester will be seeing exactly what your ECU is seeing whilst the gauge is getting a modified output form the micro controller onboard the MFU.

A couple of questions....

If you were to hammer down your bypass and stop the car quickly when you see 110/120C with the fan running. If you where to jump out and feel the temp of the bottom rad hose going into the thermostat housing, would the hose be hot or cold, ie is the stat open or closed at that point?

By any chance do you have an aftermarket aluminum radiator fitted?

Hi Roger, Thanks for the useful information, I haven’t done the hose test yet but I do have a aftermarket aluminium rad fitted, does that make a difference at all.

Hi Richard, It appears to be located in the standard position at the back of the cylinder head.

On here somewhere are reports that they can do.

I have a suspicion that the more efficient aluminum rads have the potential to mess with the normal cooling dynamics on cars with thermostats on the cold side of the radiator, particularly on the smaller engined/lower powered cars that produce less heat output.

Unfortunately the Duratec has the stat on the cold side of the rad unlike older generation cars with the stat on the hot side of the engine. On older cars the the stat was opened simply by the heated coolant exiting the cylinder head. Cold side stats are opened with a combination of hot bypass coolant recirculated through the engine and the cooled coolant exiting the rad. These two coolant paths merge within the stat housing and the resultant combined coolant temp sets the stat opening point. That's fine until the balance is upset with cooler coolant from a more efficient rad. Then the combined coolant temp will be lower and the stat no longer opens at the same point as before. It's totally counter intuitive but a bigger better rad may actually make a car run hotter rather than cooler and also make a car run hotter when the ambient temp is lower on a cooler day.

I very much hope I'm wrong with this but it might be worth trying your bypass test or even just checking when you hear the fan come on by feeling the bottom hose to see if its cool indicating the stat is shut. Normally the stat should be fully opened when the ECU triggers the fan and the bottom hose hot. And yes the Duratec will actually run with the stat closed with the bigger ali rad. It appears to derive a modicum of cooling from the coolant flow through the small bore pipe that short circuits through the header tank and the rad top header. Something that I suspect might go unnoticed.

Hi Roger, that’s certainly something to ponder and check however it seem that I’m getting a high temp reading on the gauge which is matched by the OBD readout but a laser temp gauge shows the engine temp as within the normal range. I’ve ordered a new temp sensor to start with and will give that a go. Thanks very much for taking the time to help with my issue, it’s much appreciated.