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oil cooler threads ? 1/2" BSP or M20 1.5


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Can anyone help ?

I thought I would replace my leaky oil cooler hose with some stainless hose.

The oil cooler is built into the side of the radiator.

The disco is a 1997 300tdi.

I thought the threads would be 1/2"BSP so to test bought:

1 x 1/2" BSP male to AN10 adaptor

1 x 1/2" BSP female to AN10 adaptor

The male adaptor won't fit (even a little bit) into either of the hole/threads by the oil filter.

Bizarrely the female thread will fit the threads on the cooler, and the adaptors will screw into each other

Ive been chatting the the hose adaptor supplier ( they have been very helpful) and have sent them one of my old leaky oil cooler hoses and they think its an M20 1.5 thread..

Does this sound correct ?

Puzzled of Grays


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1/2" BSP is more like 21mm diameter, so that does point to it being M20. I'm not overly up on the 300's so it might be they have a different filter housing, but the 200's and 2.5's I've had pipes made for were 1/2" BSP, and the same for the 200 rads I've worked with.

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Thanks its defiantly looking like M20. maybe its a 300 thing, weirdly the water side of it is all 1/2"BSP i.e the thermostat housing and the water side of the radiator...

The trouble im having with it being an M20 male thread on the oil cooler part of the radiator is the hose people dont do a m20 to AN10 hose fitting or adaptor. (with the M20 being female) I can get M20 to AN10 male -male adaptors so the engine end is sorted but not male -female adaptors;.

It's an allisport radiator so Ive been trying to get hold of them to confirm what thread they put on the rad / oil cooler but they dont answer there bloody phone !!!!


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I have a solution !!!

Andrew at allisport has just rung me back, apparently the later 300 Disco engine oil coolers do have M20 threads. 200tdi and some early 300's are 1/2"BSP.

Anyway, he is going to take my radiator back and re weld some AN10 fittings on it (for a small but i think very reasonable fee)

happy bunny now

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