1.8tdci is oil cooler needed?

[isetta]

My brother's Focus 1.8tdci has major coolant leak at back of engine. He is bringing it round to me in the morning to have a look at. Looking at pics of this engine it looks like there is a water cooled oil cooler on back of the engine which has two rubber coolant hoses to it. Hopefully the problem is a split hose there.

But my question is - do you reckon the oil cooler is essential. If I improvise a fix which bypasses the oil cooler will it really matter. the car is not driven hard, nor heavy laden , nor for towing.   Cars did not have oil coolers on in the past. How essential are they really? 

[TomsFocus]

It's a heat exchanger and works both ways, helps to warm up the coolant more quickly after startup and then keeps the oil cooler during hard driving.

It's not essential though.  It'll be fine to bypass it for normal driving.  

[isetta]

Ok, thanks. Sounds like it might be desirable to have it working to help demisting  screen in winter as car does not have quickclear screen.  But for now the priority is to have the car running so can be used.

[Tdci-Peter]

2 hours ago, isetta said:

Focus 1.8tdci has major coolant leak at back of engine.

The pipe run at the back of the engine is from the back of the cylinder head, through the EGR cooler, though the cabin heater, through the oil cooler, then back over the gearbox / bell housing to join other pipes near the thermostat at the front. It is quite hard to see or trace all those pipes!

Older cars often did not have a turbo, which can deliver a fair bit of heat to the oil. But the 1.8TDCI is usually such a cool running engine that I very much doubt if the oil cooler is really needed unless you drive over the Sahara with a trailer😁. But as Tom says, it does help warm up the oil on a cold start, which can reduce fuel consumption and engine wear. I can see this as I see the water temperature rise rapidly from say 5C to about 40C, then it really slows down, and takes about 5 - 10 miles to get to over 75C. I assume this is the effect of the oil cooler heating up the whole engine. In Winter, it can take over 10 miles before the thermostat opens at 80C, and then only in short bursts. I have a sensitive temperature sensor on the coolant system!