TheSamba.com :: View topic - Occasional airlock on 1600 rebuild with full flow filter

Mon May 01, 2017 8:59 am

I rebuilt the 1600cc engine on my '71 Bay last year and added an external oil filter and a larger oil pump. Trouble is, I occasionally get zero oil pressure and have to loosen the filter and disconnect the HT lead from the distributor, and get someone to turn the starter over while I watch for oil coming out of the filter housing, at which point I quickly screw the filter back on, and this always fixes it and the pressure light goes off when I start it up again. It seems to happen more often after I've parked pointing downhill, but not always, so this might be a red herring. The oil level is at max and I fitted a new oil pressure sensor. I wondered if air was getting up past the pump gears when switched off, so I've taken the engine out and removed the oil pump cover. But the cover gasket is very thin and I can't see how air could get past the gears in any significant quantity. Also I've turned the engine upside down and removed the drain plate and oil strainer. The oil pickup pipe is rock solid, and I've poured oil into it (still upside down) to see if it might have a hole somewhere letting air in, or not be seated properly in the case, but once the excess oil has found its way out to the oil pump the pickup pipe retains the oil I've poured in. So I'm stuck for ideas now. Anyone got any suggestions?

Mon May 01, 2017 9:13 am

this is usually a combination of a filter with a leaky (or non-existent) back flow valve, and a loose oil pump. A good quality filter with a good valve will help. I recommend Wix Gold or Amsoil filters. Mann is also not a bad choice.

Mon May 01, 2017 9:21 am

[email protected] wrote: this is usually a combination of a filter with a leaky (or non-existent) back flow valve, and a loose oil pump. A good quality filter with a good valve will help. I recommend Wix Gold or Amsoil filters. Mann is also not a bad choice.
Thanks for that, I'll check what filter I used - a Golf one from Halfords I think. And by loose oil pump, I guess you mean worn - I certainly had the cover plate tightened enough and the pump itself was new, so thinking it's not that.

Mon May 01, 2017 9:37 am

new pumps can be "loose", if the gears are not tight radially, and/or if they have to much end clearance. That's why you blueprint them during the engine build.

Loose pumps are most noticeable with poor oil pressure at idle.

Mon May 01, 2017 11:45 am

Is your sump extension sealed completely on the pickup tube and is your pickup tube sealed to the case. I have seen air issues caused by both of these. IF your car is pointed nose first down a hill, that means the back of the motor where the pickup goes into the case might be above the oil level and sucking air.

brad

Mon May 01, 2017 1:34 pm

slalombuggy wrote: Is your sump extension sealed completely on the pickup tube and is your pickup tube sealed to the case. I have seen air issues caused by both of these. IF your car is pointed nose first down a hill, that means the back of the motor where the pickup goes into the case might be above the oil level and sucking air.
brad
The oil pickup tube is solid in place and appears to be sealed to the case ok because I tested it and it's holding oil, and I decided not to go for a sump extension so it won't be that. There's only 14mm between the bottom of the pickup and the sump drain plate so it shouldn't be sucking air up. I didn't have this problem before I overhauled the engine and put the external filter on, so I'm thinking [email protected] suggested the cheap oil filters I'm using may have ineffective non-return valves. It makes sense. I'll check the oil pressure relief and control valves are working as well.