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Complete loss of oil pressure from 3000rpm upwards

2K views 16 replies 10 participants last post by  isus 
#1 ·
On Saturday I had a freakish failure, I lost all oil pressure while driving on a motorway, at some 4000 rpm as I removed my foot from the accelerator pedal my oil pressure fell to almost zero ( from some 5 bar)

After stopping and letting it cool down a bit, I had normal oil pressure at idle and up to 3000rpm where it suddenly cuts off and falls to zero, if the engine is hot the oil pressure warning light sometimes goes on and stays on regardless of the rpm. If you shut the engine down and then start again the light goes off, yet there is almost no oil pressure.

The engine starts normally, runs normal, no noises, no gasket failure detectable, oil level is ok, water level OK, no shavings on the dipstick.

Anyone ever heard of something similar? The small and big end bearings have been changed some 10 000km ago.

1992 A2H TS 265 000km, Castrol edge 10-60
 
#8 ·
Maybe but that doesn't really explain the low pressure light coming on. I'd suggest performing some sort of verification test before dismissing it, especially considering the major work done on bearings in the recent past.
 
#5 ·
plus one on the sending unit. ciao, chris
 
#7 ·
Did the oil pump get checked at the bearing repair. If changing the oil pressure senders (one for oil warning light and one for oil pressure gauge) doesn't change things get the pump checked. You need to remove the sump pan and the pick up tube and wire mesh. The pump is driven off the distributor drive.
 
#9 · (Edited)
Yea. The best course of action would be to remove the warning light sensor and screw in a mechanical pressure gauge to determine if the warning light sensor and gauge sending unit are bad. If oil pressure is normal, I'd check the wires next, then R&R the senders.

I got a hard time believing that oil pressure goes instantly to zero at 4000 rpm and throttle position. Sounds like the oil pressure warning light wire is grounding itself as it is rubbed by something in the engine compartment.
 
#10 ·
I believe this is a twin spark 4 banger. I'm looking at the sender first. When mine dumped, it did exactly this. The sweeper within the sender appeared t be bad and the diaphragm stopped diaphraming. ciao, chris
 
#12 ·
My gauge sender is all over the place and has been for years. Only once did the oil pressure light come on, also on a motorway, but the pressure gauge was reading fine so ignored it and it went away. Sometimes think Alfa double up on the information due to such electrical issues.
Oil pressure is mechanical and, unless your sump suddenly empties, it isn't going to suddenly drop to zero - only to later return. The senders aren't expensive and any possible oil-pressure issue does need looking into - just for peace of mind if nothing else. Reckon just the senders but unusual to have both failing at the same time. Even for an Alfa.

Good luck.
 
#16 ·
Fist check the oil pressure with a external gauge screwed into the instruments feeler. Then yo have the exact pressure. I once experienced that the instrument's feeler went bust when I chanced 10W-40 oil to 20W-50.
If the pressure measured with the external gauge is all right (4 bar) at 20 C idling you can fit a new feeler. I not OK (below 2 bar) don't drive it. Have to be pulled or pushed on a low loader.
 
#17 ·
Well on a mechanical meter engine hot, the fans started twice, at 5000 it's -2.5 bar. Iy says the same on the dash. Some 1 bar below, after 10-15 km motorway it drops to 2 bar.
Also while reving when the engine is not totaly warmed up it gets up to 4 but then drops a bit.
 
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