pontifex4

My mechanic suggested I add oil until the level is past the high mark on the dipstick before taking my car on track. What do you think? Is this common? If so, by how much?

Van

I keep it right at the full mark and have no problems.

rlm328

I would suggest not over filling. Filling to the top mark is perfectly legit. If an engine is over filled too much the crank can get into it and froth it up like egg whites, not a good thing. Just check the fluid level after every run. I usually check all of my fluid levels after each run and top off as required.

Adonay

My mechanic tells me never to overfill at any cost he states its better to fill slightly under the full mark to be SURE. However i cant back that info up on anything other than hes words and 20 years of hes track experience.

Bri Bro

And to add to this, check after every run to insure it is topped off. Too much oil can cause foaming and this makes air bubbles in the oil. Too little oil and you get starvation and then it is rod bearing time.

Richgreenster

I think that it would be better to run 20-50 wt. oil at the top of the full mark. If you over fill it the oil air separator will suck up to much oil due to foaming.

DanR

All of the above +10

Willard Bridgham 3

+1

pontifex4

Okay, deal. Thanks, guys!

Mark944na86

Clark discusses this wrt to the oil starvation problem (rod bearing #2). He says it is/was common for racers to overfill by 1/2 litre. He obviously saw no need for any concern regarding this.

So there you go. Your mechanic is in good company, at least.

Chris White

Your mechanic should be sent to the corner of the shop and have a ‘time out’ for bad advice.

I am amazed that this advice still exists. Its very bad advice.
Here is some better advice and it comes with an explanation too!

It has been noted by many that the #2 rod bearing can fail from lack of adequate lubrication. Based on ‘conventional wisdom’ (that means that they did not tyro t figure out why, they just did what worked on other engines) people assumed that the failure was from oil starvation because the oil pick up was getting uncovered and oil pressure dropped off suddenly. The fact that this happened at the track where cornering forces were much greater seemed to support this conclusion. Same thing used to happen to other types of cars too…so it must be the problem.

Wrong…in fact horribly wrong.

In reality there are four factors that cause the rod bearing problem.

1)The crankshaft is only just above the oil level in the oil pan. About ½” above. When you brake hard (like on the track) a significant amount of oil surges to the front of the pan and the oil hits a crank shaft turning at 5-6k rpm (on the track) and it does a very good impression of a blender on ‘Frappe’. Loads of foam – and once the air in entrained in the oil it does not separate out quickly. Foam is not a good lubricant.

2)944 turbos put a lot of heat into the oil – tempos over 250 are pretty standard of a stock 944 turbo on the track. Hot oil gets pretty thin, pressures drop and thin oil offers less protection. Hot foamy oil is not a good lubricant.

3)There are 90 degree bends in the oil passages in the crank shaft – not a good idea for a performance engine.(Porsche never intended the 944 to be raced and did not do any engine development towards that goal). Hot foamy oil going around 90 degree corners is not a good lubricant.

4)The oil pump has a cavitation issue at higher rpms (over 6500). Cavitation causes a big drop in pumping efficiency – less pressure. Cavitation can also introduce more air bubble into the oil. Hot foamy oil going around 90 degree corners with reduced pressure is not a good lubricant.

What makes this worse? Adding more oil!! You add more oil and there will be more oil hitting the crank and getting aerated. Those that overfill the oil are making problem worse.

On an interesting note I did an unintentional test many years ago - I was driving / instructing at the Glen and my wife was driving the 944 also. I was so busy I did not do all the usual checks – and on the third day I suddenly thought about the oil level – when I checked it there was none to be found! I added 3 quarts to get it back to mid level. So the car had been running around the track with a very low oil level and there was no oil starvation. So much for the uncovering the pick up ideas! That’s what started me analyzing the oil system in detail (10 years ago).

Van

Shoot! In that case, I'm going to run 1/2 quart down!

YZ250

Chris White's experience trumps mine, but I ran a 20 minute track session 1 qt down with no apparent issues. I normally run at the full mark with 20W50. This is on a race car with R compounds pulling 1.3G peaks in the corners.

gt37vgt

Chris i know realy just drained the oil on the sly as your misus was cutting faster laps than you ..

Chris White

Not an issue...she was never allowed full boost!!!