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

I the good owd days you would often see cars with part of the radiator or front grille blocked off in winter, partly for a faster warm up but also to stop overcooling

Neil, have you thought of trying a partial blanking piece ?

Surely the OBD is getting it's reading from the gauge, if the real time reading from the hoses is ok it must be the gauge.

Neil if your latest test was letting the car warm up by idling, your temp distributions look fairly normal, imo. The stat looks to have opened and coolant is flowing as you wouldn't want to keep your hand on that 66C bottom hose! The rad temps might be a little adrift but that again might be down to your laser limitations and the emissivity of the bright metal surface? Also by 110 I think you should have seen the second higher fan speed kick in. Was 110 the highest it would go before the fan brought the temp back down again?

So the stat looks to be opening normally when stationary, but is it opening when you are motoring and you are seeing those 110/120 head coolant temps?

The fan was on max speed at 110 Roger, when I’m motoring it can go up to 120 and then drop slowly back to about 100-105 when the engine is not pulling hard. It’s really weird that the stat temp appears to be normal at around 85-90 according to the laser but the gauge is reading 110. Jon M has suggested blanking off a portion of the rad to see if that makes any difference but it seems to me that it’s some kind of electronic issue because the OBD and gauge reading are near enough identical and the OBD is getting its info from the ECU, or am I wrong assuming that? It’s giving me a headache🤔

That's good Neil. Sometimes there can be an electrical fault that stops the fan low/high from coming on.

The coolant in your cooling system isn't at a single temperature. There's a huge variation throughout the system. The coolant is continually moving the heat from the hottest parts of the engine and dumping it in the cooler radiator where its removed, so no surprise the coolant will be at a different temp depending on where its measured. Your 110 reading is taken from the sensor recording the coolant temp exiting the cylinder head, so pretty much the hottest location and that's what the gauge is also seeing. By the time that coolant has traveled down to the stat it will have lost heat and also merges with the cold side rad coolant.

Yes I've previously posted up a blanking plate solution when I discovered that my cold side stat in my 1.8 Duratec was staying closed whilst moving and causing very high temps. Its totally counter intuitive or bonkers to blank a radiator in an attempt to cool an engine, so was waiting to see if your stat was actually behaving the same.



I don't think there is an issue here. Effectively the ECU and gauge get their info from detecting the same returned voltage produced by the temperature variable resistor (thermister) in the head sensor. However the gauge gets it indirectly as it first passes through and is interrupted by the MFU before sending on to the gauge. What you see on the OBD is exactly what the ECU is seeing. That's my understanding for what its worth.....

Me too, I find more gin helps

Thanks Roger, I think I’ll try to blank a par of the rad to see if that makes any difference, thinking of taping some kitchen foil as a trial.

Surely the long term answer must lie with an alternate thermostat. As Rog says, it's totally bonkers to correct an overheating issue by reducing the efficiency of the rad.

Thermostats respond to a heat dynamic, a blanking plate can't.

Neil only attempt the rad blanking if you are 100% certain that your stat is staying closed when you are traveling but opening normally when stationary. Your last test indicated that the stat was opening but you didn't confirm it was stationary?

The blanking plate in my pic is on runners/sliders so I could experiment with it in differnt positions. Mine work better at the bottom on the portion of the rad that poked out from under the car rather than at the top as in the pic. Also whilst I saw an improvement it could have been better. I had planned a larger one but never got around to it before moving to my current +4. If you are going experiment by blanking the external grill, go for a much bigger area maybe say 50% ?

When you do the test monitor the temp VERY carefully with the OBD rather than the gauge. If you see it approaching 120 stop immediately and remove the the blanking as obviously its not working. Don't go beyond the temps that you have already seen before as you are into potential head/gasket damage territory. I never actually saw 120 with mine, I think 115 was about the highest I ever caught on the OBD, my gauge was useless in that car.

Richard reiterates a valid point. Yes its bonkers to blank a radiator in an attempt to cool a car so yes of course do this at your own peril. Regarding the thermostat, that might be one difference between your car and mine. The first things that I did after checking my orig 90C stat was working in a pan of boiling water was to replace it with an alternative 82C stat, the lowest I could find. I didn't notice any difference with that stat but left it in anyway, so bare in mind that my car had a different stat to yours and the blanking plate.

Good luck

I tested the new the new thermostat before fitting it and it opened at about 85 degrees so I’m pretty sure that it’s working. What a head scratcher this is🤔🤔

Has anyone ditched the thermostat and used the likes of a Davies Craig electric pump with it's programmable flow to maintain water temp.?


K