| Non-GMC - VW Cabrio oil pump diagnosis [message #89608] |
Wed, 23 June 2010 09:57  |
hertfordnc
Messages: 1164
Registered: September 2009
Location: East NC
Karma: 0
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This group saved me with my last troubleshooting mystery on this car. I've tried the VW forum but it has not been helpful.
- the car has 160,000 miles
- low oil light comes on after the car has been running a few minutes. longer if it's cold.
- there is ticking in the top end after the light comes on but not before.
- It consistently comes on under the same conditions. I think that rules out a bad sensor.
I'm thinking oil pump.
AM i correct in thinking that if it were a bearing or some other serious problem there would be other symptoms? lack of power, knocking, etc?
Any other diagnostics?
thanks
dave
Dave & Ellen Silva
Hertford, NC
76 Birchaven, 1-ton and other stuff
Currently planning the Great american Road Trip Summer 2021
It's gonna take a lot of Adderall to get this thing right.
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| Re: Non-GMC - VW Cabrio oil pump diagnosis [message #89618 is a reply to message #89608] |
Wed, 23 June 2010 11:08  |
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burtco99
Messages: 31
Registered: September 2007
Location: Montreal
Karma: 0
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VW had some issues with main bearing clearances on some of the 1.8L 8V engines. The clearances were not enough to make any extra noises, but they did have an effect on oil pressure when the engine was hot. The oil pump on these engines is also notorious for needing replacement at the mileage you have. Many need replacement much earlier. Ultimately, the only long-term solution is an oil pump and/or bearings, but many have just run thicker oils, or oil additives like STP.
The ticking in the top end is a symptom of the low pressure as the lifters require decent pressure to keep quiet. The repeatability of the symptoms also tells me the problem is mechanical, but I have seen electrical problems in the pressure monitoring system that were extremely repeatable as well.
Another less likely cause of your low oil pressure is worn or loose cam bearings. These engines have pressure lubed cams that run directly in the aluminum head casting with no inserts. I have occasionally seen excessive clearance in the cam journals that required line boring to correct.
You don't specify if the low oil pressure warning triggers at idle, or only when driving or revving the engine up off idle (2000-3000rpm). This generation of VWs use a complex oil pressure monitoring system that has 2 pressure switches. One switch triggers the light if pressure is less than 15psi. The second switch monitors oil pressure AND RPM through a special module and will trigger the light if oil is less than ~35psi with RPM over ~2000rpm. I am not certain of the exact specs, but this is pretty close. The oil pressure problem is an annoying one as the oil pressure light is tied to a warning buzzer that is hard to ignore!
If the light is triggered at idle, then you possibly have a bad switch, a very tired engine, or an electrical problem affecting one or more wires in the oil pressure monitoring circuit. I strongly suggest a mechanical oil pressure test to confirm the problem.
If the light is triggered when engine is revved above ~2000rpms, you need to test with a bit more detail, again a pressure gauge test is recommended, but you also need to identify at what rpm the light triggers at. This is easily done with engine warm and slowly raising rpm till light comes on.
If the warning is triggered close to 3000 rpm, then an oil pump will definitely help. you can also try replacing both pressure switches with units from a similar year Jetta Turbo Diesel. The Turbo Diesels have an identical oiling system, but due to the oil feed to the turbo, as well as piston oil sqirters, the pump is not able to maintain as high a pressure at a given RPM. VWs solution was simply to use switches with a lower pressure setting. I've driven over 100k additional miles on angine using this trick and the engine oil pressure did not get any worse.
If your oil pressure drops below 15psi at idle when hot, or the warning is triggered near close to 2000rpm, then you need to consider more serious repairs as these symptoms indicate a heavily worn engine. I would certainly pull the oil pump and examine it for wear and excessive clearances. While the oil pan is off, pull the center main bearing cap (thrust bearing) and examine the bearing insert and crank journal for signs of wear. The VW cranks are tough so you might be successfull at doing an oil pump and bearing swap without pulling the engine.
Hopefully you have a better idea of what you need to do. if not, I'm sure you'll recieve addequate help here.
C Ya!
Les Burt
Montreal
1975 Eleganza 26ft
A work in Progress
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| Re: Non-GMC - VW Cabrio oil pump diagnosis [message #89620 is a reply to message #89618] |
Wed, 23 June 2010 11:23 |
hertfordnc
Messages: 1164
Registered: September 2009
Location: East NC
Karma: 0
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Thanks. that was exactly the sort of answer i was hoping for.
If i install a gauge and cut out the buzzer and light, what do you think is an acceptable oil pressure to avoid damage?
I have a parts car with a lot less miles on the engine so my long term plans do not include serious engine work. I just don't like the car enough. I'd rather work on the Coach.
dave
Dave & Ellen Silva
Hertford, NC
76 Birchaven, 1-ton and other stuff
Currently planning the Great american Road Trip Summer 2021
It's gonna take a lot of Adderall to get this thing right.
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| Re: Non-GMC - VW Cabrio oil pump diagnosis [message #89635 is a reply to message #89623] |
Wed, 23 June 2010 16:53 |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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Dave, Several members of the GMC Tidewater Crabs have sent you e-mail about your surplus GMC parts coach. Please reply of one of them.
Tom Phipps
220 miles away from you.
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: Non-GMC - VW Cabrio oil pump diagnosis [message #89650 is a reply to message #89635] |
Wed, 23 June 2010 20:13 |
hertfordnc
Messages: 1164
Registered: September 2009
Location: East NC
Karma: 0
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Tom,
i sent an email to you on Jun 13. Must be net voodoo.
I'll reply here; another GMCer here in NC has expressed interest in taking the whole thing but he can't do anything until July so I'm waiting for a definite answer from him.
If he opts out then the tidewater crabs are welcome to it.
Should have an answer in a few weeks.
Dave
Dave & Ellen Silva
Hertford, NC
76 Birchaven, 1-ton and other stuff
Currently planning the Great american Road Trip Summer 2021
It's gonna take a lot of Adderall to get this thing right.
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