MFI fuel/oil mixing

[Flieger]

I have a 2.7 liter RS spec engine with MFI. When I drain the overflow tank or check the oil, I notice a gasoline smell and the oil seems very thin.

The oil pressure is good. I have the usual 10 psi per 1000 revs. At 4800 revs, I had 60 psi today, running ~185 degrees Farenheit stable. At idle on start up, I have about 40 psi. The oil temperatures are good. Running hard, the front oil cooler works and the temperature never gets above 190 F, even on very hot days and vigorous exercise. The engine runs strongly and has a lot of power. The oil filter area has a leak because it used to be very overfilled when my mechanic changed the oil and filter. As a result, I smell and see oil smoke at stops.

I don't hear any unusual noises from the engine such as knocking. Everything seems to perform well.

Is it normal for some fuel to mix with the oil with MFI? If I have a serious fuel/oil contamination issue, would I see very low oil pressure and high oil temperatures?

Thanks for any information.

[Jeff Higgins]

No, even a little fuel in the oil is nver normal in an MFI system. Any at all is unnacceptable and must be addressed immediately, if not sooner. It takes very little gasoline contamination to significantly reduce oil viscosity. You won't see an increase in oil temps or a decrease in pressure as the oil thins from contamination. I guess maybe, in extreme cases, but it would certainly be too late by then.

Does the oil level actually appear to rise over time? That is a very clear indication you are getting contamination. If you are, stop driving it until you get it fixed. This really is a serious issue. You might consider sending an oil sample to one of the testing labs to verify whether or not you have a problem.

[Flieger]

Thanks for the reply Jeff.

The oil level does not go up. The oil level was about 1/2 quart too high after the last oil change. It is back to normal now. It is not like large quantities of fuel are being dumped into the oil. The oil leak around the oil filter area is probably just a leaking fitting or gasket.

I would suspect to see a decrease in oil pressure and an increase in oil temperature if there were a problem.

Can you give me the name of a lab to send an oil sample to ? What does it cost ?

Thanks !

[Grady Clay]

Jeff is right on. Oil dilution with gasoline is a very serious issue.

Most significant is with serious dilution, once the engine is warm, the gasoline can quickly boil off leaving nothing (or too little) to pump through the engine. Of course the oil-gasoline mixture is not a sufficient lubricant. This is particularly true at the cam-rocker arm interface and rod bearings. If you see higher temperatures or lower oil pressure – too late.

You should change oil twice in a short period of time getting the engine hot. Add a third change with a front cooler.

You need to find why there is oil dilution. Has the engine been started often and not driven? This is not uncommon if the car has been in a workshop or body shop.

Is the cold running thermostat turning off soon? Is it getting sufficient hot air? Does the cold start solenoid completely turn off? Haw is the maim mixture? Part throttle mixture? What do the plugs and exhaust look like?

I would do your first oil change (with sump inspection and new oil filter) before you start it again.

Best,
Grady

[zotman72]

My 2.4S MFI engine's oil was getting contaminated with gas for several years. I tried to live with it, changing oil every 1K miles, different injectors, valve adjustments, cleaning the plugs all the time (and new ones) and finally resigned to rarely driving it. Last summer I really wanted to go an extended trip to the Durango 911E Rendezvous with my car and did not want to destroy my motor due to oil dilution causing extensive wear on bearing surfaces. I made an appointment at the best MFI shop in Denver (or within 1500 miles for that matter), Eisenbuds. The work did not get done at Eisenbuds that appointment day so I turned to another Porsche shop as a fall back, thinking they might be able to fix things if I gave them "proper directions" as I knew pretty much what the problem had to be (bad thermostat) based on Check, Measure, and Adjust procedures. However it did not go that way at all. The second shop kicked me out of their shop in the process destroying our 10 year relationship ($25K+ their way) For they were erroneous convinced that is was my Pertronix, worn distributor and combined with new plugs were the solution. I knew otherwise and said fix the thermostat (and was correct) and the rest can addressed later if needed. They countered with get your POS car out here and do not come back. Ironically, this shop's motto was "We listen to our customers." The next day, I finally got Eisenbud fix the thermostat and made the Durango trip. http://66.236.61.177/showthread.php?t=349295&page=7&highlight=Durango The lesson here is: MFI expertise is a rare comodity and you need to be self sufficient as much as possible, and if you must go to a Porsche shop for MFI help, choose it based on their record of MFI expertise, not on a mechanic's confident bravado. YMMV
Yeah do get that oil dilution issue fixed, I would recommend check the thermostat rod and see if the clip holding the rings has sheared.

[Grady Clay]

Bill,

Aside from the rant, what was the issue with your car? Was it the thermostat as you suspected? If so, why not fix it yourself, an easy repair.

Most of the shops are my former (20+ year ago) employees and are very well versed in MFI. In fact I paid for John to attend Bosch MFI school when he worked for Rennenhaus or before (pre-'71). Greg and Pat are equally skilled. I think even Chris keeps up his skills between golf rounds. For the really old timers Karl and Vern are still around.

My argument to every MFI owner is to become your own best diagnostician. If you present a knowledgeable MFI tech with a written report of every detail of your CMA (and CMA2) procedure and results, you will probably find greater help.

I can’t imagine why you got kicked out of a shop. Perhaps it wasn’t MFI related.

You can always report your symptoms on this forum and get good advice.

Best,
Grady

[Flieger]

Originally Posted by Grady Clay

Jeff is right on. Oil dilution with gasoline is a very serious issue.

Most significant is with serious dilution, once the engine is warm, the gasoline can quickly boil off leaving nothing (or too little) to pump through the engine. Of course the oil-gasoline mixture is not a sufficient lubricant. This is particularly true at the cam-rocker arm interface and rod bearings. If you see higher temperatures or lower oil pressure – too late.

You should change oil twice in a short period of time getting the engine hot. Add a third change with a front cooler.

You need to find why there is oil dilution. Has the engine been started often and not driven? This is not uncommon if the car has been in a workshop or body shop.

Is the cold running thermostat turning off soon? Is it getting sufficient hot air? Does the cold start solenoid completely turn off? Haw is the maim mixture? Part throttle mixture? What do the plugs and exhaust look like?

I would do your first oil change (with sump inspection and new oil filter) before you start it again.

Best,
Grady

I don't have a hose connected to the MFI pump's temperature sensor. I have no heater. There is a screw in the place where the hose should be but the engine runs well and I was never concerned about the set-up.The mixture seems to be fine, as there is not an excessive amount of backfireing, there is good power, and I do not smell a lot of gas or see high engine temps(lean). I have no accurate means to measure the mixture, though. The car starts well, even without the hand throttle up and the part throttle mixture seems just a little rich, but normal. There are occasional backfires on over-run.

I will change the oil soon for a valve adjustment. I'll look at the plugs then.

Can you reccommend a lab to analyze my oil?

Thanks for the help!

[ttweed]

Originally Posted by Flieger

Can you reccommend a lab to analyze my oil?

Try these guys.

[john walker's workshop]

no preheat hose to the t/stat eh? looks like you self diagnosed it already.

[eapcpa]

Looks like you have three options going forward. Reconnect the thermostat and re-tune the system. Call Henry and get his manual thermostat conversion setup so you can re-tune the system. Or re-tune the system toward lean without a thermostat but you will compromise drive-ability at some point in the warm-up cycle. You will certainly reduce the engine life if you leave it as is. The MFI was engineered as a system to promote performance, drive-ability, emissions, and economy. Cause and effect dictates that if you change one parameter of the designed system you will affect the drive-ability at some point. You may be able to live with 1000 mile oil changes or poor cold running or whatever. I can tell you a properly functioning MFI system is very rewarding to drive and is dependable. Just my .02

[Jeff Higgins]

Fliegler, could you snap a photo of what you have right now, in the area of the back of the pump where the thermostat is, and post it? I'm confused. You say there is no hose to the "temperature sensor", but there is a screw in its place. Hmm... there is no "temperature sensor", so I suspect you mean the thermostat. Also, if just the hose were missing, it is unlikely there would be a screw in its place. A lot of guys take the whole thermostat off, and replace it with a screw like the one Ed mentions (as supplied by Henry). So, let's see what you've got on the back of that pump. That's "back" in car orientation; the side you can see easily from the back of the car.

[Flieger]

Originally Posted by Jeff Higgins

Fliegler, could you snap a photo of what you have right now, in the area of the back of the pump where the thermostat is, and post it? I'm confused. You say there is no hose to the "temperature sensor", but there is a screw in its place. Hmm... there is no "temperature sensor", so I suspect you mean the thermostat. Also, if just the hose were missing, it is unlikely there would be a screw in its place. A lot of guys take the whole thermostat off, and replace it with a screw like the one Ed mentions (as supplied by Henry). So, let's see what you've got on the back of that pump. That's "back" in car orientation; the side you can see easily from the back of the car.

Here is my set-up:




I am told that this is a common modification for race cars without heaters. The pump may be set to run a little rich all the time, but not mix oil and fuel. I cannot simply reconnect the warm-up hose, as there is no attachment point on the heat exchangers, which have had the heater part cut off.

[Flieger]

here's a zoomed in view of the pump:

[Jandrews]

Subscribing

[Jeff Higgins]

Yup, that's kind of what I suspected. You are right; that is a very common modification to enable the deletion of the somewhat troublesome thermostat and heater hose. Not just on race cars, either.

So it sounds like you never change the setting on this. Correct? If it starts easily when cold, and you never fiddle with this, then I would suspect the screw is not in all the way. The screw (or the rod on the old thermostat) is meant to push on an arm inside the pump body that will lean the mixture as it moves forward. The full rich, cold start setting is all the way back (again, back of the car "back"). Full lean, where it should run when warm, is all the way forward.

You should be able to turn the screw with your fingers. See if you can turn it further in. Don't use a wrench or horse on it; when the internal lever stops, you'll feel it. Most guys have a big wing nut style screw head on these to make them easier to turn, but you should still be able to do it with your fingers without one.

If it goes further in than where it is right now, you have been running too rich. Too rich may cause excess fuel to blow past the rings, unburnt, and into the crankcase. Correcting this by properly leaning out the warmup circut sure would be the cheap way to fix your gas-in-oil problem. "Cheap" as in "free". Hope that's it...

[Flieger]

Thanks for the advice, Jeff

I have a feeling that that is what is causing the richness. I hope that this is the problem with the fuel/oil mixing.

The richness did not seem to be so excessive so as to cause fuel and oil to mix in the crankcase, as I would think that there would be backfiring or other problems with the engine's performance if it were that rich. The engine runs smoothly but I will check the mixture. I would like to lean it out, anyway, and I hope that the fuel and oil are not mixing inside the MFI pump because that means a lot of $$$$ and sending it to the legendary guru known as 'Gus'.

It seems like there should be a "jam" nut on that bolt to keep it tight. I have 1 nut on it and I can just barely turn it with my fingers. Perhaps the bolt backed out a little.

Thanks again for all the info and advice.

[Jeff Higgins]

MFI can run very rich without the symptoms one would expect from a carburated or CIS motor. The fuel is atomized so well by the 230-240 psi injector pressure that it will still continue to run well. It will stink like hell and put out a black cloud worthy of any dump truck, but it won't backfire, cough, sputter, bog, or anything those other systems will. It just loses a bit of power, and contaminates the oil.