Technical Question - Oil Cooler

[gdaybruce]

Having replaced the valve stem oil seals last month I took the car for a decent trip of some 150 miles on Saturday and all was going very well until 10 miles from home when the temperature guage started to climb. I pulled over asap and on lifting the bonnet was greeted by clounds of steam and a hissing sound coming from below the inlet manifold. When things had settled a bit I removed the radiator pressure cap, limped to a garage to refill and then, leaving the pressure cap off, drove carefully home. There didn't seem to be much further loss of coolant

The fault has to be, I think, either the head gasket (perhaps I damaged it while refitting the head) or the small bore pipe that runs from the oil filter housing to the back of the cylinder head. This is described on MX5 Parts and Autolink's web sites as the "oil cooler inlet pipe". Only one problem; my car is a 1.6 and that pipe was only ever fitted to the 1.8! I spoke to Autolink this morning and they confirmed this is the case. It would seem therefore that a previous owner (I'm guessing when the car was in Japan) modified the car to include the oil cooler, which is located in the housing for the oil filter.

My question is, has anyone else come across this modification and does anyone know what difference this oil cooler makes to temperatures? Presumably much less than a proper oil radiator but Mazda must have felt it was appropriate for the larger engine.

My next problem is that I think the head is going to have come off (again) because the pipe is totally inaccessible at the back of the head. At least that means fitting a new gasket as well as a new pipe so I should fix the fault either way!

[MX-5 Lazza]

I think it's probably badly named. What it probably does is speed up the warming of the oil by running hot water through it.
Are you sure you have one? There is a core-plug under there somewhere and I've seen them rust through and cause a coolant leak.

Edited by MX-5 Lazza on Monday 24th May 21:41

[gdaybruce]

MX-5 Lazza said:

I think it's probably badly named. What it probably does is speed up the warming of the oil by running hot water through it.
Are you sure you have one? There is a core-plug under there somewhere and I've seen them rust through and cause a coolant leak.

Edited by MX-5 Lazza on Monday 24th May 21:41

I guess a core plug is a possibility although it would seem that the leak is only apparent when the system is pressurised. If a plug had rusted through I'd expect it to leak to some extent at all times. Still, I'll have a good look.

I came across this pipe unexpectedly when I took the head off last month. I noticed that neither Rod's manual nor Haynes mentioned it but never guessed that that was because it wasn't supposed to be there!

As you say Lazza, I'd guess that it is an oil heater when the engine is warming and the coolant heats up quicker than the oil but perhaps also a cooler when the oil is stinking hot but the coolant is no more than 90C or so. My car also runs v high oil pressure - 6 bar when cold and 4 to 5 when hot. I've changed the oil sender unit on the assumption that the old one was faulty but it made no difference. I'm now thinking that the same previous owner who fitted the 'oil cooler' probably also changed the oil pressure relief valve spring. Taken together with the blanking bolts fitted into each branch of the inlet manifold which suggest water injection (or nitrous?!) and I have a picture of a foced induction engine set to run high oil pressure and driven within an inch of its life! Or perhaps it was all for the pose factor. I'd love to know!