Low oil pressure 803cc

[pde2000]

Thanks Liam. Yes the oil is a lower rated modern type, which is what i have to hand. I am dropping in on my dad later, where he claims to have kept a couple of cans of old duckhams Q in the garage. One good thing about using a gallon of modern oil for a bit is that it will have given everything a clean. These modern oils are designed to be used with full flow filtration because they pick up every little bit of crud. Old oils allow a nice layer of gunge to settle out in the sump.

I think you're right about replacing the engine and box eventually, with a 948. I sold the plate a few years ago to survive a lean patch so can hardly claim to have kept it all original. It was 155ATW and is now 656XUS - who cares?

[pde2000]

The Duckhams Q has brought up the pressure a bit, it's just a regular 20/50. Cold start is now less energetic but once warm the engine sounds less tappity than with the synthetic. It's a bit frustrating that heritage oil now costs more than fully synthetic. Another thought is that the coolant gallery of the block is clogged, as that will get the oil hot. When i got the car i tried emptying the block and nothing came out. Having taken the tap off i took it out for a drive only to find that all the coolant escaped and had to refill, but there was still no coolant coming out of the tap hole, very odd.

I have taken a hacksaw to a tecalemit filter to get inside and see whats what. It's not that the orifice is small, but rather that the filtration material is very impermeable. Even when the oil is warm not much can get through the material, whereas the new filter is more like a modern full flow type so is a good filter, but just lets plenty of oil through (as it should if it was full flow).

[pde2000]

download/file.php?mode=view&id=1099

Here's something i was not expecting; the bypass filter has a bypass. The little hole in the end of the filter cartridge allows oil to bypass the filtration, and is smaller than the restricted orifice leaving the filter. Oil comes in and surrounds the cartridge with some getting through this hole rather than through the material. The cartridge is pushed against the end plate by a spring and has a rubber seal, so when the can is cut all the way round it pops open.

So it's not a dummy, but not particularly worthwhile in my opinion. Better off with no filter and better pressure, using old fashioned non-detergent oil, like the side valve engines.

edit; the restriction diameter is 75thou, about 1.9mm

[liammonty]

Good to hear that the oil change has improved the pressure a little, and also a good idea re using a low detergent oil if you are running no filter, though I'd still be inclined to go for a filter with Declan's corrective restrictor. Morris Golden Film is a decent quality low detergent oil that is available as 20W50.

It was interesting to see what's actually inside those filters!

[oliver90owner]

The amount of oil being bypassed is controlled by the inlet orifice - less pressure, less oil bypassed. The smaller hole will prevent the filter from over-pressure.

The bypass filters on my tractors - designed before 1930 - had an inlet orifice (with jiggle pin, to avoid blockage) a PRV to avoid over-pressure and a spring loaded valve which prevented any oil being bypassed below 8 psi, I think. Simple to check if it needed cleaning - just feel if it was warm when the engine was hot - and a quick scrape-off of collected dirt from the felt media, or change of cotton waste packing (dependent on the type fitted) when it did not get warm enough.

Bypass filters are generally not regarded as best option for steel backed precision bearings, but were good enough for engines with rather larger clearance tolerances with thick white metal bearings.

Nowadays, the bypass filters, installed on some vehicles, is designed to filter out sub-micron sized particles in conjunction with the usual full flow filtration, thus extending the oil change intervals very considerably.