Erratic Oil Pressure
 

I have already gone through about 40 different threads without finding an answer. In my race car, which I just pulled out after sitting for a year. I changed the oil, fired it up and everything was good. Took it out for a test day and the car made very good power and we felt it was good to go.

Some background may help. It is an S4 4 port with s5 NA internals. It has a TII oil pump and Racing Beat high pressure bypass. It starts and idles cold (1500 rpm) with 40 - 60 lbs oil pressure. Touch the throttle and the oil pressure buries the gauge at around 120 psi. Hot pressures are 30 lbs at idle and again rises to over 100 psi at 4000 rpm. Oil temps in the 170 - 200 degree range. Oil used (3 changes) Mobil 1 20-50, RedLine 20-50 and Mobil 1 20-50 V-Twin oil which was recommended by Mobil 1.

What I am noticing is wild oil pressure fluctuations while I am out on the track. The Autometer gauge swings between 100 psi and 40 psi after coming out of a corner and running down the straight. Its almost like the pickup is sucking air, but the oil levels are fine and it has the Racing Beat anti aeration plate. With no changes to anything from the last run. When I come back into the pits the oil pressure is around 20 psi for a moment then rises to 40 psi and if the car is sitting I can pick up the revs to 4000 rpm and the oil pressure is still over 100 psi. Its like the oil is sloshing around.

What also bothers me is that the oil levels remain the same, but the oil looks like water and just runs off the dipstick when hot. During the 3 oil changes there have been no metal flecks in the oil and the coolant levels have remained the same. Could it be a gauge problem? Could it have a stuck bybass valve?

Ideas would help a ton.

Eric Nummelin

First thing I'd try is to increase the oil fill level and see what happens to the pressures, as you said, it might be sucking a bit, and with a rotary, overfilling it somewhat won't really hurt anything (no windage).

Could you be getting fuel into the oil, diluting it, causing it to run off the dipstick like that (smell it)? You could always take an oil sample, send along a new control sample and get them tested to see what's up with the oil, rather than just guessing. There's probably a lab around your area that does that sort of thing that might be willing to do the job.

Another way out possibility is that the pickup tube is cracked and hard cornering is opening it up, allowing air in, then it closes up again after the corner and the pressures go back to normal.

Thanks for the ideas. Oil dilution is one of the first things I checked. No fuel smell at all. What is interesting is that the oil looks like water as well. Its almost clear when hot. I can barely see it on the dip stick. Very strange. I am going to go back to 40 weight Redline. I used it in my old motor for years with no issues. It just takes a while to heat up before running hard. It really annoys my pit mates, LOL.

Good idea to overfill the sump. It may help. I am also going to try bleeding the line to the oil pressure gauge as well. It has a loop in it that may have some air trapped in that.

I will also look into a cracked pickup tube, But I am a bit reluctant to pull the engine out unless I have to.

Good ideas to start with. I appreciate it. Anybody else have any ideas??????

Eric

i think i would start with simple stuff too.

go back to the other oil. did you change filters too?

Check for oil leaks. I had a micro fracture on one of my banjo fittings from my dual oil kit and my oil pressure was pulsating down the back stretch at Mosport (when I noticed it at least). It would only leak when under pressure.

thewird

What rpms are you running?

Look real close at the dipstick as soon as possible after some sustained hi rpm track time. Do you see lots of small air bubbles/foam on the dipstick?

Where is your oil temp measured? After the cooler (where it is coldest), or in the pan (where it is hottest?)

Just curious, what are you running in the way of a PCV or catch can?

What about the front o-ring? Could it be that the thick, cold oil isnt thin enough to leak past it? Once the motor is warmed up and pushing high pressures, it forces oil between the front cover and iron?

Speedturn - I was looking for bubbles in the oil, but I didn't see any. Like I said before when the oil is hot its like water and no air bubbles could stay in it. The oil temps are measured in the pan where the old oil level sensor was. I am turning up to 9,000, but this past weekend I was only pulling about 7,500 to 8,000 as the track was damp.

Gene - The oil catch tank is a JAZ with big vent filter on top. I have used this setup since 2004 with no issues. I also added a vent filter through the top of the oil filler tube, through the cap to maximize breathing. This issue is a new development with no changes to anything.

Shainiac - I understand what you are saying, but the oil pressure surges as I go down the straight and around corners with little to no pattern.

I got an idea from the ausrotary site. They suggested that I may have air trapped in the gauge line. The line I am using was too long so I put a loop in it to take up the slack. They suggested that I crack the line at the gauge with the engine running to bleed off the air.

I am going to try this this afternoon. I will let you know.

Eric

This happend to me, it was the gauge (of course it was the last thing I checked) My gauge has an oil pressure sending unit on the block. Air gets trapped in the diaphram (sending unit) and the oil pressure goes nuts. Anytime I reved up it went back to normal, and was weird at ilde also. This occured after sitting for a long period of time. Changing the sending unit fixed it. If your gauge is oil feed then your gauge might be junk. Get the autometer gauge with a sending unit, it's safer and only costs a little more. Thats my 2 cents anyway.