Last Thursday headed off from home in West of Ireland to attend Volksworld show. About 10 miles out on the motorway at 60mph noticed that the oil pressure needle (new vdo gauge and sensor) would slowly drop from about 4 to 2 bar then return to 4 (always drives at 4 for past 3k miles since got the van - T2 1973 1600 twin port - bog standard everything) This was happening about twice per minute. Then after a few more miles it started to drop to 2 then down to near 0 and the oil light would come on for about a second !!! Came off at next junction checked oil level and wiring etc (all ok). I then made an “executive decision” to turn back and get the day car and the tent!! As above happened all the way back home I’d say the light came on more often - Made the show in good time in the day car and it was well worth the hassle!! What could be causing the problem ?? Brian
I'd check the wiring again, and then suspect a duff sender. Hard to think how your oil pressure could fluctuate in that odd fashion. Obvious: you have got a decent oil level? If it'll do it with the van stationary, worth chucking a mechanical pressure gauge on it to check.
This may be way off but last time I did an oil change, there had been none in for days and the engine was stone cold. When I turned it over to get the oil circulated I couldn't get the oil light on the dash to go out. Also no oil was appearing at the sender port. I reasoned this was due to the pressure/temperature relief valve doing its job. The pressure sensor port and the oil cooler don't get any oil if the valve is doing its job according to Haynes. I overcame this by placing a 500W inspection lamp underneath to warm up the engine and all's good now. It occured to me that if your relief valve was sticking this might affect the pressure reading. Mine's a type 4 so I can't tell you where to look on your 1600.
One reason for the high speed pressure fluctuation could be that the oil is getting hot and the oil level has dropped a bit and is starting to froth up so air gets in the pickup. So on mine the pressure will be 38 psi and flicker down to about 32psi for a moment.. For me, that is time to fill up from the lower line to the upper line on the dipstick .. I have a very fast acting digital gauge with a picture of a dial.. with 10 updates a second so it never sits still but it gets more flickery .. This is usually coupled with the oil temperature starting to rise a couple of degrees. It could be an air leak where the oil pickup goes into the engine block . Then the oil pump fills with oil/ air froth and loses pressure until the oil flow slows and the air stops being picked up then it re- primes and the pressure builds again, and the cycle repeats.. You were probably right to turn back.
Guys you are amazing! Some very incisive replies!!! I’m still on the ferry back but will get under the van tomorrow and start the diagnosis!!! If I had decided to continue with the trip past experience told me I’d arrive in Pembroke and about 5 miles out the road I’d be thumbing a lift to Volksworld while planning a cross-water vehicle recovery I’ll keep updates coming……
That sounds more likely to be the pump lost prime, unlikely to be the pressure relief valve sticking and there is always some oil flow through the cooler regardless of whether the oil is hot or cold.
This^ All very well theorising on oil frothing and air leaks but the clue to the problem could be the ‘new vdo gauge and sensor’. Check the easy things first – the last new bit fitted.
I have seen a Druine Turbulent aircraft fitted with a VW engine do the same thing, full p/x when climbing, then a 'clonk' when you level off and the p/x reduces to half. Another 'clonk' as you start to climb again and full p/x returns. The crankshaft had snapped and was broken at an angle allowing the crack to open and close.(end float) Tony
Just checked the oil level and its about 1mm below full.... Will investigate more fully this afternoon
Obvious wuestion: if you've got the dual terminal sender, the connections are on the right way round? Gauge to "G", oil light to "W"?
Only today managed to get back to diagnosing the problem: I fitted a t-piece and attached an oil pressure gauge - its a Durite with a 12foot capillary tube, passed the pipe out through the drivers side engine air vent and was able to wedge it in the sliding window on that side so I could see the gauge in the mirror while driving. drove about 40miles mostly motorway at 60-65mph - could not reproduce the problem!!!! - oil pressure stayed rock solid about 3.75 BAR/45psi it only changed marginally when I was off the motorway and doing about 40mph Oil Temp was about 90C. ???
Just for clarity -Both gauges were in use for my test The vdo sender in now pointing down at around 45 deg whereas before it was horizontal That’s the only difference!
So, maybe you disturbed something while you were teeing in the mechanical gauge, inadvertently fixing it? Whatever, so long as it's a gauge wiring fault rather than an actual random loss of oil pressure that's a result.
