When running the engine to temp then always have the reservoir still sat on the battery box. This will be then the highest point. gently increase the revs to 3000 rpm and then hold it there for 5 minutes. You should also have the temp set to max hot coming out of the vents and it should be really hot.

I have not heard of the grey genuine 180 t/stat droping mpg. I have fitted this to many Disco's 2 and have not had any one say this. Equally well I have not seen this on mine.

 

burp it, burp it real good...
and try tightening-up all of the hose clamps (if applicable). also, have a look at all the hoses, at temp. back a while, I had a hose ballooning on me, and only did it at temp. would suck air in with the ballooning, replaced hose, re-burped, all was well.

 

Thanks, I will check for any bulging in hoses and bleed the system at the higher RPM with bottle raised and heat blasting after I install a Genuine LR 180 Thermostat. Will get back with results next week, thanks again.

 

Back when I swapped to the grey OEM 180 t stat my temps dropped drastically. I get 15mpg on average.

 

Have you checked your condenser fan it should have come on around 115 drgrees

 

I haven't heard that fan come on for over 2 years now. I ceramic painted my manifolds and it hasn't been on since the day I put them on. To this point the UG never registered temps above 206.6 even on the hottest summer days.
Since last post I have bled the system 3 times and gotten air out and eliminated water trickle sound under the dash however temps still range from 210-221.

 

Would a blockage in the radiator possibly cause this temp elevation?

 

you can check your radiator with a digital thermometer.
Ij

 

So as a recap, I had this temp spike out of nowhere after years of my truck running at a range of 190-205 on green 50/50 Prestone and a 192*F thermostat. New range became 205-221. I change in this order and with no difference after each; Coolant temp sensor, 180*F thermostat, new OE radiator and today the viscous fan assembly. It has been bled again and again throughout this and all hoses are intact and new as of last year.

I am pretty certain my condensor fan does not work any longer as it has not come on as my temps hit 212*F, however I think it has been broken for far longer than my temp issue has existed.

My new theory is, please correct me if it sounds crazy, the temps seemed to rise as the air temps in my area began to remain in the teens and low 20's. I put ceramic painted manifolds on several years ago and definitely notice a dramatic decrease in under hood temperatures( no more oven blast to the face even in summer time). Ive noticed my intake air temps are only in the 40's and my engine compartment is quite cool after driving around.

This leads me to believe my engine compartment hasn't been reaching a temperature high enough to engage the fan clutch this leading to my elevated coolant temps especially at idle. I will have to wait until it warms up around here to find out I suppose. I still welcome any other suggestions and I hope this isn't a symptom of a bigger problem. For now I'm going to just ignore it.

 

So I haven't been able to ignore my temps, still running 204.8-210 on the road and idling at 221-230. I've done radiator, coolant temp sensor, viscous fan works properly, condensor fan works when it's supposed to, 180 tstat, water wetter, coolant resevoir cap the proper 1.4 bar stant one, multiple bleeds the proper way and exhaust gas in coolant test multiple times all with no results.

So tonight I idled it up to 230f and used a thermal imager camera to shoot temps around the engine.

My results are;
Upper radiator hoses and thermostat 170-180
Heated core lines 227-230 in and out
Coolant temp sensor in the valley 227-230
Coolant resevoir 206-210
Oil pan 160

Heater and condensor fan have no effect on temps whether on or off.

I have no measurable coolant loss and with no exhaust gasses in the coolant detected I thought I could rule out cracked block and head gaskets. My oil and coolant do not appear to be mixing either.

Any other suggestions from anyone what could conceivably cause this much heat and not give me any real diagnostic clues?