22/07/2026
Well, this year’s fun driving has proven to be short lived and surgery is being undertaken!
In the last few drives the dash would flash up warnings of low oil pressure when hot, at tickover. This would go away with even the smallest raise of revs, then pop up again when at idle. After a bit of experimentation and observation, it seemed prudent to first change the pressure sensor. Sadly, this gave the same result and left me with only one option: check the oil pump, its pickup and O-ring. Unfortunately, due to the construction of the chassis, there’s no way to remove the sump and front cover without removing the engine. So here we are!
Engine out and inspected. Firstly, as the problem was only intermittent and the PDM / dash give live readouts, it wasn’t driven with low pressure and the clean metal-free oil has shown that. A check of the crank bearings has shown they are perfect and look brand new, big relief! The oil pump pick up is spotless and the O-ring is happy…
After further digging, what isn’t happy, is the pump itself. Externally, it looked fine, but with the cover and gears removed, I noticed the bypass plunger was stuck very slightly open. When the spring cover was removed, the spring itself popped out and was fine. So why was the bypass plunger held open slightly? Look closely at the inner casing: there are cracks forming in the casting, including a big one above the bypass plunger, likely snagging the spring and preventing the mechanism from closing properly, bleeding oil pressure at low revs.
This is the original GM oil pump, which was installed at factory. It’s lasted a good few years and occasionally gets revved harder than a stock engine would allow (my engine revs to 7.2k), so I can’t be too miffed about its death!
A Melling higher pressure oil pump has been ordered, but with the motor out, t feels like a few more “upgrades” are necessary… plans are being formed, watch this space!
