When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I suspect my engine is burning oil due to valve guide wear. On the exhaust side, this is a photo of the valve. Having never examined valves, I don't know how to judge them. All six exhaust side pretty much look like this one. The intake side is much cleaner, but I suspect that is from getting "washed" by fuel.
Steve - would there ever be a benefit to walnut planting the carbon off the back similar to what BMW and Audi owners are doing in the intake side with direct injection issues? Obviously won't solve the route issue regarding the valve guides.
Exactly - don't panic just yet and stop driving the car. :-) It does not look good, and yes you are burning some oil, but we need more parameters, like mileage on the car, some history and oil consumption.
I jumped the gun and already dropped the engine and took all the "peripherals" off it. Rather than panic, I was glad to have the excuse to tear my car apart :-). I posted the picture to double check before touching the engine internals though.
To answer your questions, the engine has ~77k miles. I've owned the car the last 2.5 years and in that time I estimate my oil consumption has gone from 1qt/1500 miles to 1qt/750 miles. The last couple months I estimate at being even higher than that (very roughly about 1qt/250miles).
A couple other things I noted:
1. My fuel economy has fallen below 10mpg in normal driving
2. Black residue on air filter where the "feedback" tube enters the housing (maybe unrelated, see part 7 in the diagram below).
PS. Mike -- I love pcarworkshop and really appreciate your efforts on it.
How do we know at this juncture, if its valve guide wear as opposed to oil blow by, the rings?
I admit there is oil being burnt here, but the source is generally not ascertained via a photo. Would it not be more prudent to rotate the crank until the exhaust valve is open and check deflection of the valve stem with a dial indicator, buy push/pulling in a few locations to try to determine valve guide clearance/wear/potential out of round condition?
I don't claim to have Steve W's experience in things of this nature, but the methodology I suggested could be ascertained without dropping the motor and pulling the heads, yes?
Steve may suggest that if there is ring wear and the valve guides were still in decent shape, then you would not see these kinds of deposits...Jus thinking out loud here...
First, I ALWAYS recommend performing a leakdown test before engine disassembly for these very reasons. Properly done, this allows you to determine whether the rings are sealing properly or not, thus helping to isolate the source of any measured loss of cylinder pressure. This is SOP around here. In most cases, the pistons & rings are just fine; its the worn guides that need attention.
About the guides,.......to date, after doing hundreds of sets of 3.6 heads, I've never seen any 993/964 engine that didn't need guides, unless they were already replaced.
Porsche's fitment at the factory was, in many cases, far too loose and even beyond their own stated wear limits noted right out of the factory manuals. Rennlister Bill Hutchinson's 3K mile 993 C2S guides were well outside of factory tolerances and that was the lowest mile example to date!
Certainly one should remove the lower valve covers and measure/assess the lateral movement of the valves in the guides, but at 77K, I'd wager anyone that they need replacement.
Naturally, this is all MHO so please accept all this in the manner offered.
2. Black residue on air filter where the "feedback" tube enters the housing .
That is a vent tube from the clutch housing. I don't understand the benefit of blowing abrasive clutch dust into the air intake with the potential for some of it to ending up in the engine. Also with the OE configuration when one is not careful with the clutch the cabin heat air intake that is in the engine compartment sucks in the fumes and pumps them into the cabin adding that pleasant German Roast Clutch scent, very refreshing! I am considering rerouting the pipe out under the car where it belonged in the first place!
Have you revealed the engine previously? If not, you might want to replace the various gaskets while you have the engine out. Your oil loss could be leakage as well as burn off.
That much of a drop in fuel economy alarms me. Check you on board computer for codes, make sure you don't have a failed O2 sensor or something that might affect the fuel economy more directly.
03-28-2015, 06:49 PM
Is this exhaust valve guide wear
