Type 4 Start Up Oil Pressure Lag - Fixed it

[SGKent]

There are many threads here where T4 owners of late T4 engines have a delay getting oil pressure when the car has been sitting. This occurs on new and used engines. The proposal I made 10 years ago is that once air gets into the over pressure return loop on a late case, it aerates the oil, which in turn causes the oil pump to cavitate. The work around was to start the bus, let it run 3 or 4 seconds, shut it off, wait 7 - 10 seconds and do it again. Usually one had oil pressure in 8 - 12 seconds of run time. However if the engine was just allowed to run, the oil could take 25 seconds or more to come up to pressure. Early cases dumped the excess oil into the sump. On a late case it circulates round and round thru the pump and cooler until it gets used. On a late case, over time sitting, the oil drains out of that port just enough to let air replace enough of it to cause the cavitation.

On my last two engine builds, I decided to seal the return area case halves, being careful not to use so much sealant that it could end up in the oil flow to the pump. This morning was the big test. The old GD engine used to take the normal 25 seconds to get oil pressure when it had been sitting, unless I did the start - stop - wait - start thing. Today I started the engine after sitting 3 weeks and only 4 - 5 seconds to get pressure, totally within reason for an engine that has been sitting almost a month.

You can see the return port on a late case in the image below. When you build an engine with this style case, be sure to seal that oval between case halves. Also be sure to use an oil filter with a return check valve. Any air that gets into that port will get sucked round and round causing the pump to cavitate.

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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[Takamotti]

Good info, thanks. Never noticed it before (have the same TM info in german) that they say "after relief valve" , I thought these engine cases were always without the second pressure valve?

[SGKent]

[raygreenwood]

[SGKent]

Ray - on the late case the issue is that as the oil drains down to the sump it sucks air into that passage slowly. Then instead of the air getting ejected, it goes back into the pump and froths causing the pump to cavitate for lack of a better word.

The pressure relief valve used to dump into the sump so any air was ejected. In the last cases VW routed that dump back to the oil pump inlet so any air being ejected goes right back into the pump pickup, upstream (closer) to the pump than the pickup tube.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[RalphWiggam]

Huh. Did not know this.

My early 1.7l case takes maybe 5-6 seconds to build pressure after sitting for awhile. You can really tell in the sound once the pressure comes in. My dash light and pressure gauge both confirm at the same time.

I thought I had read here that 1-2 seconds was normal and I always wondered why mine took 5-6 seconds. I was worried something was wrong.

[Wildthings]

Don't have much experience with the later cases, as for my own engines I have mostly kept with 1800 cases and parts. However I learned long ago that on hard turns and steep side hills you can see your oil pressure drop if you are running the recommended amount of oil in the sump, so for most of the 1/2 million miles I have driven a Type 4 engine I have kept an extra quart of oil in the sump. Outside of having to raise whatever side I am adjusting the valves on slightly to keep oil from running out, I have not found that it causes any problem. I would suspect an extra quart of oil it would help with the problem SG Kent is talking about.

[raygreenwood]

[SGKent]

[Wildthings]

[SGKent]

Mike I don't question that your buses are really special. But I do know that if oil gets up to the level of the crankshaft, the oil becomes like a taffy wrapped around the crankshaft. It froths, it heats up. That is why some high performance cars use dry sumps, or if wet sump they use a windage tray. Late racers even put scrapers on the crankshafts to wipe oil off it. That frothing and taffy creation of the oil makes heat, puts air into the oil and robs horsepower.

I made this post for people trying to solve the lag getting oil pressure on a late bay. Adding thinner oil, an extra quart did not solve it. Many of the people who had the problem sold their buses and moved on a long time ago, just like I plan to soon. Just thought I would leave a fix for future bus owners who have the issue. I am glad you get a million miles out of brakes, clutches, and engines.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[richparker]

I always prime my T1 engines if they have been sitting. Could doing that possibly help prevent this issue in a T4?
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[SGKent]