Tonyrandl

Hello everyone, I'm after a little help with a sight problematic 996 4S. I bought this as a project as the engine was suffering with scored bore. It's the 3rd 996 engine I have rebuilt but this one has been extremely problematic.

The car is a 2005 C4S in Atlas grey, Tiptronic with a lot of factory options and just 98k.
The engine was stripped and the block was re-sleeved by a well known company in Bolton (UK). The engine was re-assembled by myself with no issues but when it got to hot idle after the engine was re-installed, it indicated an oil pressure issue at 0.5 bar which tripped the lights. A mechanical gauge was fitted directly to bank 2 which showed the same reading. Some oil was removed and it had a distinct shimmer to it with flakes in the oil filter.

I nearly cried as it had only 30 mins of idle on it!
Engine was removed again and partially stripped. I found that bank 1 intake cam had picked up on the bearing seat and worn. It looks like like the oil way had become partially blocked with RTV during rebuild.
The engine was completely stripped down again to the crank, extensively cleans and rebuilt with a replacement cylinder head, refitted and it started up. Oil pressure is very good until its at hot idle and the pressure dropped back down to 0.5 bar, 6-7 psi and rises with revs.

I'm running through a list of areas that could be of concern but I could do with some help as its becoming quite frustrating.
The engine sounds great, even when at 0.5bar, no ticks, knocks or anything and no CEL (oil is clean)
During the rebuild, it had new main/big bearings, pistons, chains, guides, IMS, gaskets, AOS, oil cooler, oil pressure sensor, oil filter housing, oil pump relief valve was replaced with the upgraded parts and bolts. The oil pump shows no wear inside and the crank was within specification during re-build. Current oil is a quality 5W-40.

I have found that bank 1 chain tensioner is faulty but not effecting tension and no apparent oil pressure loss but I have a new one on order.
Does anyone have any ideas on this? - next on the list of areas to check/replace are the sump oil returns/seperator and change the oil pump (incase there is an issue that I can't see with the current one)

I feels like I'm just throwing parts at this now - any help is greatly appreciated.

Porschetech3

Always start with the simple stuff first.....check the oil filter to see if it has crushed...( you never mentioned having replaced or checked it )

Remove the sump and check to make sure the pick-up tube is not blocked with excessive sealer ( you mentioned a blocked port in the head to cam bearing).

I know you mentioned a new oil pump by-pass valve and spring......but didn't say when ,before or after the first or second attempt .......make sure the new one is working properly and not sticking....

Pull the cover off the oil pump and inspect the main oil pump gears and housing, ( you can also check the by-pass valve while the cover is off much more effectively)

If you don't find the problem after these things, then you will have to go into the engine again looking for the loss of pressure...

hardtailer

Is your current observation based on the OP gauge of the car only or have you confirmed it with the external pressure gauge?

If the former, then it could be the sender reading too low.

Tonyrandl

Sorry, should have mentioned that. Yes, the filter is in perfect condition and is genuine Porsche filter that came with the new filter housing and the sump is clean.
The pump gears are showing no wear and are clean. I'll take a look at the bypass valve/spring later this week and put a borescope camera up. Thinking about it, it could be getting stuck if its even slightly damaged.

Tonyrandl

I've hooked up a manual gauge on bank 2 where the sender usually sits and its reading 0.5 bar (6-7 psi) at idle. Pressure at cold, warm and even with load applied to the engine is reading very good oil pressure.

binaryaudax

Any chance the scavenge pumps are oriented incorrectly? Would that cause oil pressure to be low?

De Jeeper

i was thinking the same thing.

Porschetech3

It would have to have both scavenge pumps oriented wrong to have low pressure at idle, but it would be even worse at RPM's and the OP is stating the pressure is ok at rpm's and cold...(?)

I have seen engines run for 10k miles with only one pump oriented wrong, albeit was probably driven like a Granny...

It would be smart to verify them though...

We really need an accurate oil pressure data at full temp and 4k rpm to ensure the pressure is at least 50 psi at the head @4k rpm..

If the pressure is only low at idle, I would suspect the piston oil squirters are stuck open....they are spring loaded to not operate at hot idle to keep the pressure from being low, they only start squirting when the pressure is ~ 30psi..

Tonyrandl

Both pumps are set to the correct orientation but I've been thinking. How much should usually drain from the engine when bank 1 tensioner is removed? - I estimate 2-2.5 litres drained out which seems excessive. is it possible the oil is pooling in bank 1 head?

Tonyrandl

At hot idle, the pressure goes to 4 bar (50ish PSI) at 4k revs. It increases/decreases nicely with no jumps on either gauge. I'm really hoping its not the oil squirters as I'm rebuild no 3 within 2 months is hard work!

meirschwartz

squirters were replaced during first or second build?

Tonyrandl

They weren't replaced. Ive never replaced them in previous rebuilds. I've never checked the price of them but I've recently discovered they cost next to nothing........

allcool

With your (re?)sleeve job, did you get the Capricorn pistons with 2 piece spiral wound springy thing oil rings..? What size is your engine..?

Mpfaff

We’re the squirters removed from crank carrier to clean oil passages?

Tonyrandl

They were re-sleeved with nikasil liners using Mahle OEM pistons