Hi can you help. I've just bought a defender with a disco 200 rid engine. It's runs well but runs red hot. It didn't have a thermostat so I've put a new one in. I've changed the radiator for a brand new one as all the fins were missing on the old one. And I've put a new temperature sender unit into the thermostat housing. Still it's red hot after five or ten miles on normal road. Is there something I'm missing?????

Air lock?

If it's got a disco 200 tdi the sender a gauge will not match try and get hold of an infa red temp sensor and point on thermo housing or you could get a sender from steve Parker or better still get a tim capillary gauge.

Hi johns thanks but flushed system when replaced radiator. Wangie many thanks that makes perfect sense and obviously I was missing something. Feeling somewhat stupid now but thanks anyway. Regards j

Why aint you fitted a new waterpump?

Never trust the temp gauge, always check the top hose and thermostat housing with a temp gun, for me a general rule of thumb is, if you can hold the water pump to radiator hose, all ok, if you can't, then there's something wrong

1spin water pump looks new gasket sealant still fresh so didn't bother. Dave 90 can hold pump to radiator hose when gauge showing hot so do believe it gauge compatibility. One on order so well see if it sorts it. Thanks gents

Englishrover said:

1spin water pump looks new gasket sealant still fresh so didn't bother. Dave 90 can hold pump to radiator hose when gauge showing hot so do believe it gauge compatibility. One on order so well see if it sorts it. Thanks gents

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Nice one That's the only trouble with gauges, they make you paranoid, I was going to put an oil pressure gauge on mine, but all it would make me do is watch it constantly and crap myself if it went too high or too low

I've had the miss matched sender problem too!

Diesel Do said:

I've had the miss matched sender problem too!

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I put the old TD one in the disco 200 when I put it in the 90

Bummer! In that case you do need to actually measure the temp to see if it's lying or not! does it boil and chuck it's water out? The fact it had no thermostat suggests its not a new problem. If its not the original engine you need to check all the plumbing to make sure they haven't done something bloody stupid! Start it from cold let it idle heater on keep moving around all the pipes in turn you should feel them getting hot in a sequence. Heater supply then return, rad hose from stat may get slightly warm then should get hot quickly as the stat opens, you should then feel the heat move thru the rad and back to the engine then the header tank will start to get hot! There's small bore pipe from the stat housing and the top of the rad that go to the tank, these should get hot too, these bleed air to stop air locks. The t piece can block or being a transplant worst case could be blanked off! If the rad isn't getting hot, could be blocked hoses, air lock, corroded or broken pump, stuck stat (but you said it didn't have one in b4 so unlikely)
Big thing tho is, does it actually boil? Does it chuck it's water out? If it hasn't and doesn't you do need to measure the temp first or you may be doing loads of work for an electrical fault?! If you google it you should be able to find resistance readings for the temp sender you've got, measure it with a multimeter calculate what temp it's reading, then actually measure it and compare your readings!
That's what I'd do any way but I'm just a grease monkey!

I'm a dick, got confused and replied to the post above thinking it was you saying you had put the correct sensor in and it was still doing it! Must read thing properly. Bugger, now I've got a sore finger