Quality thermostat

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Originally Posted by Linds

Some time ago I replaced the original black plastic tee with a brass tee. From what you are saying, the replacement part does not replicate the original. Perhaps this is why I had problems today?

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Yup. The black plastic thingy has a restrictor jet in the hose from the thermostat. If your brass tee is arranged so the straight through flow is directed to the expansion tank, it has some minor suction effect on the rad air bubble. You could modify the tee with a small copper tube in the inlet side to replicate the OEM plastic thingy, although it sounds like you've finished the bleeding already. After the engine and heater are bled automatically of air, the only other place for air to collect is the radiator. Bleed it off any way you like and you're safe until next time you work on the cooling system.

Linds, My t'stat also takes a quite a few k's/mins before it opens up. and is a relatively new item...pot bench tested etc.
I reckon that with the bypass purge line the engine is effectively continually mixing quite a stream of 'warm block' coolant with 'cold' coolant downstream of the t'stat (radiator, exp tank, hose etc), which may explain the time taken amongst other items as discussed.

I am a bit paranoid about the purge line becoming blocked (as it was when I purchased my Disco) so every so often shine a LED lamp on the side of the expansion tank (clear type) and can easily see a surprisingly strong flow that comes from the bleed outlet on the t'stat housing....this flow also sucking in cooler radiator fluid.

ps. when I bleed mine if I have pulled hoses off everywhere etc, I unscrew the expansion tank mounts and carefully raise it above the engine and heater hoses etc as someone here had done (sling it with some string from the bonnet catch), then add from there, thus highest point in the system and some good head to purge through to t'stat bleed. But if your purge line is the factory piece (with venturi) and working well, probably just the service manual way is good enough.

Thks for the replies.

Well I bled mine by simply topping up at the thermostat until the expansion tank was full then putting the lid on and continuing topping up until the thermostat housing was full. Then run until warm and let it cool down (overnight)and then top up again at thermostat housing. Repeat until thermostat housing stays full. Then I siphoned some out of the expansion tank( to just above seam) and it has been ok.

I found the old plastic tee piece - but it does look flimsy ( and is now about 15 years old-and have been known to break IIRC) to me so not going to use it.

The old thermostat I took out was a Waxstat with a 78 degree stamp on it. Apparently the one I put is is rated at 88. Indeed I am seeing higher temps on the TM4 now - up to 92 today 35degrees, 110 with aircon on. It doesnt get up to temp much, if any, quicker than the old one though - so maybe that is just how D1's operate, or the oil thermostat is stuffed as mentioned earlier in this thread?