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A-Series & Oil Coolers

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dklawson

dklawson

Yoda
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This pertains to my Mini but there's a lot more A-series discussion here than there and what I need opinions on can come equally from the Spridget world.

My Mini was originally built with an oil cooler. On the early cars like mine, the mount was vertical and attached to the engine on brackets that hung it below the generator. Since I've switched to an alternator that's no longer an option and the body work does not allow the fitment of the later horizontal cooler used on Minis and Midgets. I've always had what I consider low oil pressure (even after rebuilding the engine with a new pump and bearings). I decided to squeeze in a horizontal cooler to improve the idle oil pressure but I had to settle on a cooler quite a bit smaller than the ones run on later Minis and Midgets.

After installing the cooler I had to really crank in the relief valve spring to get my oil pressure back up. Apparently the hoses, fittings and cooler add a lot of pressure drop themselves (the gauge connection is after the filter and cooler). I used 6AN fittings and hose, I probably should have used 8AN. That said, I was still struck by the new, low, oil pressure readings.

After adding the cooler I'm seeing an hot engine idle oil pressure at 900 RPM near 30-35 PSI. Through the RPM range my relief valve still seems to be doing its job of holding the peak pressure close to 65 psi cold, 50 psi hot at anything over 1500 RPM. It's the idle pressure that bothers me.

There was a significant drop in my oil pressure after installing the cooler and this leads me to believe that the pump I installed had "marginal" tolerances when new.

Finally... getting around to the reason for this post, the questions.
What size oil lines and fittings have most people fit if you made your own instead of buying off-the-shelf hoses?
Have any of you seen problems with new oil pumps having loose tolerances that gave you lower than expected oil pressure?
 
Doug:

I was thinking that 30-35 psi at 900 RPM in a hot engine doesn't sound too bad.

If you're getting 65 cold, your pump can't be that bad (I'm assuming your running 10W-40 or 20W-50).

As for oil coolers, I've never bothered to run one in my 1500 race-Spridget or my old 1275 race-Sprite. The more tricked-out 1275 Sprite I sometimes co-drive doesn't have one either.
I understand their value in a 130 HP production racer that shifts at 7500, but I wonder if the rest of us really need them?
Part of my reason to avoid them is that they trap a lot of junk even if they are only a few years old (and they are virtually impossible to clean out). I've seen several original MGB oil coolers that were hideous inside.
If I truly wanted to run one, I'd replace it every year.
You might find that running a cooler thermostat will make a bigger difference to oil pressure than an oil cooler.
Have you tried running your car without the cooler?
 
Thanks Nial.

I haven't had a cooler on the car for the seven plus years I've owned it... until today. A previous owner removed the cooler and during the restoration I sought a used one "just to have". All the changes I've made to my car are reversible and I wanted the ability to put the factory cooler back on should I ever sell the car.

I know I shouldn't worry about the pressures I'm seeing except that I rebuilt the engine only about three years ago... which means there is probably less than 8k miles on the engine since its rebuild. I"d like my hot idle pressure to come up a bit and hover closer to 40-50 psi. Perhaps it's just wishful thinking.

BTW, I took the used oil cooler I bought and left it soaking inside with paint stripper for about two days after which I reverse flushed it. A lot of nasty stuff did come out. I don't pretend it's pristine inside, but it's not the cooler I'm running either.
 
When my engine rebuilder rebuilt my engine he showed me the old oil pump and the new oil pump he installed. There was a significant difference at the in and out locations of the two pumps. Also, he "ported" the two locations where the oil flowed so the oil didn't have to go by square corners. Both these things made sense to me, Idle oil pressure hot is 50-55psi, running at rpms 80psi.
 
On my street car I saw the same thing until I added a thermostat to the system. There was so much pressure drop when cold that my oil pressure went down with increasing RPM’s. This is with -6 fittings and hose. That said, your pressures sound fine. Any more back pressure you put on the system above 10psi / 1000 RPM is just a waste of horsepower.
 
Hah! Thanks Chris! My low oil pressure is just a performance mod! Now I feel better. /bcforum/images/%%GRAEMLIN_URL%%/smile.gif
 
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