Hi there,
I am the owner of a Defender 90 , 200 tdi engine . Since I own it, 6 years ago, the temperature runs always too low, in Summer or driving up hill it goes a little bit up but then the needle turns again less than half of the gauge. Two weeks ago, my alternator belt went off and both voltimeter and temperature gauges showed me that something wasn't right and I could see the temperature rising almost to the red zone of the gauge. This made me think the gauge was working fine.
I decided to change the timing belt and water pump as well as the alternator because those pulley bearings had a little bit of play causing the alternator belt to jump off the pulley. This solved the problem due to the play on the pulleys.
Well, as I finished the timing belt I put the new water pump in and decided to change the sender and the thermostat, because as I said before, the landy was always running too cold. I also did a flush to the cooling system and dismounted the radiator to be checked and cleaned. Once I put everything back together I decided to dismount the thermostat and use rain water instead of antifreezer to fill the coolant system in order to let the engine run for a while, check leaking spots and to wash the coolant system for the last time before draining and refilling with coolant. So far everything worked fine, hoses where hot as spected and the gauge didn't rise that much. (With no thermostat mounted)
I drained the rain water and refilled with antifreezer and put the new thermostat on. After a while with the engine running the gauge was rising up to the end of the white zone and the top hose coming from the thermostat was cold and so was the radiator, heater and bottom hose were hot. This made me think that the new thermostat (Bearmach) didn't work well. Then I changed the new thermostat (Bearmach) and put again the old one (genuine) and everything seems to be as it was before I changed the timing belt or even touch nothing in the engine. (Needle less than the half of the gauge).
I noticed the genuine thermostat had a whole where it was supposed to be a little pin and I thought it probably went off after 29 years in the thermostat housing and I decided to buy a new one but this time a genuine land rover one. Well, the new genuine one was identical as my old genuine one just the new one got the pin on it.
I put the new genuine thermostat and let the engine run almost 40 min. The resault was again the same as with the Bearmach one, the temperature rised to the end of the white zone of the gauge but the top hose was complitly cold and so was the radiator.
I don't think that two new thermostats are broken showing the same temperature and acting the same not opening at 88°C ( at least that's what I think when they reach the end of the white zone of the gauge).
It is also strange that the old genuine thermostat did not have the pin which make me wonder if someone before me (I am the second owner) had the same issue with the temperature and decided to fix it just taking off the pin of the thermostat in order to let the coolant passing through.
I have been told that the problem might be air on the coolant system but I don't know what to think.
This issue is driving me crazy 'cause I don't know how to solve it, if someone has any idea I really would apreciate your help.
Many thanks to everyone
Marcos (from Spain)
