Sorted the DSP. It was in Cathedral mode so I just switched it off for now. Will play around with it once everything else is fixed.

It doesn't seem to be losing any coolant but I'll keep an eye on it over the next few days.

Pulled up the coolant temperature from the hidden menu and it sat at 112 - 114 during a half hour test drive so all seems fundamentally ok. However, I didn't get the needle moving up like it did on the motorway yesterday. At least the engine seems not to be overheating so I'll just wait until the next long trip and pull up the temp diagnostic again.

I suspect that it must just be a dodgy gauge as I can't see any reason why it would only overheat when cruising at a steady 70.

AndrewT wrote:

I suspect that it must just be a dodgy gauge as I can't see any reason why it would only overheat when cruising at a steady 70.

I dont want to alarm you but that sounds very high! The system, is designed to run between 93-105C so yours sounds high. I would suspect the stat as its rising and falling, but to high. The coolant system is pressurised so can operate about 100C but 114C would be causing me alarms. Just as a thought if you change the stat and still get no luck i might look at the water pump not circulating correctly. Just to put it into perspective my 30min journy home @ 70 running on LPG (will run slightly hotter) the max temp i got was 96C and that was slowing down on the sliproad. The max temp ive had was 105C and that was sat on my drive while i refilled the coolant system after chaning the rad. I would get it looked at sooner rather than later as you could be doing more damage due to excessive heat. If the gauge is showing an increase then its usually very hot. I would also post in the more technical areas of the forum as this could be easily missed and there are alot of knowladgeable people on here who could help.

I think I understand..... the engine is running under minimal load with lots of air cooling so the thermostat closes a bit to keep the temp up. Then it starts to warm up under load (or reduced flow through the rad) but the stat sticks until it gets very hot then it pops open. Makes sense.

I must admit, the fact that it's got two separate thermostats was making it harder to work out what the problem could be.

Oh no.... there are 3! that i know of anyway. The electric stat is there to help open the mechanical stat. Its a wax block with a heater coil inside. When you floor it or the engine detects extra load it grounds the elec stat which preheats the coolant thus opening the mech stat prior to the engine temp increasing due to this load. There are mods to permanently ground the elec stat to cool the system permanently. The mech stat should start to open at 88C. When the engine is cool the stats closed and bypass's the rad, as the temp increases 88> the stat starts to open allowing coolant through the rad to cool. Yours isnt opening so bypassing the rad. Your stat is either goosed (not opening due to failure) or sticking. So your temp within the engine keeps increasing until the stat pops open and allows the coolant through the rad. At this point i would have thought your stat would stay open but its not????? Possibly the wrong spec stat from previous owner? The 3rd stat is the transmission cooler stat. not 100% sure how that one works but that cools the transmission fluid with the coolant so you COULD be cooking you transmission.

I think it's 110, not 88, thankfully (see other thread).

88 is when you disappear back to 1955.

The rest makes good sense though. This is a great forum for learning stuff.

Think we might have to disagree here. If the middle of the gauge is 75-113C i would hope the stat was opening before 110C as a small increase in temp due to whatever reason, which is possible would alarm the owner who might possibly themselves and take the car back to dealer due to a minor fluctuation in temp and stat acting slow. BUT if it was working between 80-103C this would allow for those situations. Second graph and quote from page 12.
My understanding is the stat opens between 80-103C. It does however have an electric bit which will force the stat open if 110C is reached or certain cond (p10) are detected by the DME (computer brain) forcing the stat to open at lower temps.
I would say that as good as the info on the other page is it's not easy to understand. I wont be to upset if I'm proven wrong and interpreted it wrong as knowledge of the system is what im after. So will be more than happy to be wrong but have the correct info.

It looks as though the stat opens at 103c at the engine coolant inlet which equates to 110c at the engine outlet which is where the temp sensor is.

The article is a bit confusing as it chops between inlet and outlet temps. Doesn't help if you've been on the beers.