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

That looks clever Keith. Never thought of fitting one of those.

But... I came so close to throwing the 'cold side' stat away completely by removing it from the housing. Then back to basics and fitting a simple 'hot side' stat in the top hose inside one of these.



At least then it might work like a proper engine should

Rog, completed the static test. On tick over the top hose got warm and bottom hose stayed cold until 85-87 when the thermostat activated and the bottom hose warmed up. On tick over the car maintains a temp reading on gauge and OBD of 87. Put a few revs on and temp gauge crept up 98 and fan kicked in, left on tick over and fan stopped at 96 on OBD. Back on the revs and gauge went up to 110 but OBD read 103. Checked top and bottom hoses and could hold both, the top being hotter than the bottom. Laser check showed top at 80 and bottom at 61, coolant expansion tank read 90-92. So there is a discrepancy between gauge and OBD reading. Back on the revs and gauge went up to117 and OBD read 110 but still able to hold both hoses (just). So the stat is opening when stationary and travelling so the rad blanking is a no-no. As I see it the car is running no hotter than 110 according to the OBD but surely this is incorrect as I can still hold both hoses and the laser readings show significantly lower temps.🤔🤔🤔🤔

A proper mystery, this one.
Leaving no stone unturned, maybe check as best you can that the head gasket isn't blowing into the coolant system.
Look for any traces of white emulsified oil on inside of filler cap; even a compression test on all four cylinders.
A shot in the dark perhaps, but something ain't quite right!
Good luck.

Yes the static test looks normal to me as it warms up during during idle, stat opens when it should, fan lowers temp nicely.

Just a bit unclear about the traveling fast along the bypass test. Can you remind me again, what temp would the metal portion of the bottom hose be if you stopped the car quickly, jumped out and measured it after observing the high 110/120 OBD temps?

NB- The analogue dash gauge is little more than an ornament. You cant make precise measurements with it. It's sluggish and suffers from hysteresis so no surprise that you see a discrepancy between that and the digital output from the OBD/ECU that will be sampling many times per second. Probably best to forget the gauge during these tests.

At 110 the bottom hose read 66 with the laser.

No, none of those dreaded blown head gasket symptoms thank goodness, just had a full service and nothing cropped up either.

And just to be absolutely clear (sorry ), that was observed after stopping the car quickly and taking the measurement after traveling fast?

There is a subtle difference here as there is an additional cooling effect from the extra air flow through the rad whilst moving compared to any stationary test.

Still for me its a thermostat issue. Designed to fail open they often get sluggish and tired in function. I think it tries to open but this happens only partially so the first time the engine reaches full temp the stat opens as far as it can. Water flows into the rad and cools to exit at the bottom hose, engine cools and stat closes. Now as the engine re-heats, the next time the stat opens,but not as far so you get water flow into the rad but slowly. this cycle carries on until the stat opening function weakens further and the radiator through put becomes slower and slower. The engine now holds onto its heat for longer but does eventually cool enough to allow the stat to close but soon you build retained heat in the engine which doesn't dissipate enough and quickly builds again. The stat by this time is at its weakest opening function. You might not even be getting enough heat through the rad to even trigger the fan heat sensor! A properly functioning system when the stat opens and reaches the bottom hose... well you ain't going to be able to hold it! To maintain an effective heat drop from water leaving the block to that returning is in the region of 10'c this enables the engine to maintain the optimum operating temperature band. This is why fitting too large a rad is not a good idea if it can cool the returning coolant at too low a temperature.

Get a new stat and gasket, then remove the old stat. Try not to damage the gasket/seal and refit the housing without the thermostat. Now run the car and see what happens. You should fail to reach operating temperature. check the flow across the radiator header tank, you should clearly see movement, if not the water pump needs looking at.

If all seems well I would now take the opportunity to flush the system. Get a flush product, Halfords sell Prestone and it's pretty good, in fact having tried many over the years I think its the best and its also suitable for alloy rads. After emptying the flush solution repeat a couple of times more with plain water to fully clean the system out.
When this is finished refit the new thermostat and gasket. Check the engine spec for the correct temp stat and believe this more than the indicated opening temp stamped on the old one. At this time go around all the hoses and squeeze them looking for weak areas/failing hoses, It would not be the first hose I have seen which was suffering from an internal delamination of the internal lining and this can restrict flow, in your instance pay particular attention to the top hose. Refill the system and see how it performs. If when half way through filling you can't get anymore coolant in and you haven't got the full required amount in just start the engine and the pump will draw it in, then continue filling until full. make sure your cockpit heater control is set to max heat and fan on first setting. As engine warms up you should feel warm air entering the car confirming the heater matrix is full. When system is full to the header tank cold or lower level mark put the cap on and run for a check.

Yes👍

I’ve just fitted a brand new stat that I tested and saw it open at 85 degrees. Haven’t tried a flush through though yet.👍