Oiled the track - trying to diagnose
 

Hi, all,

I had my 993 at Grattan last weekend. On Friday (instructor's day), I had an oil line pull loose from the thermostat block that sits near the lower oil filter (just forward of the oil tank in the right rear), leading to a massive oil dump on the track (and the car). There are two oil lines that come out of this block and run forward to the front oil cooler. Only the topmost of the two lines pulled out by about an inch, revealing the internal gasket. There is a bracket that holds both oil lines in, and it had bent. I took the car to a nearby Porsche shop, and the owner pushed the oil line back in, straightened out the bracket, reassembled it, and tested the system. He thought I might have pranged something while trailering the car, though there was no evidence of anything touching the oil lines. He said I was now good to go.

Back to the track, where I ran several sessions that same day with no problem. I checked the position of the oil line after every run, and it was holding.

The next morning in the first session on the track (45-50 °F outside), the same thing happened after about two laps. Quite embarrassing and inconvenient for everyone while the mess was cleaned up, but no incidents due to my spill. Same oil line, bracket bent again. I put the car on the trailer for good.

A few details: There is a Cargraphic oil cooler installed in the front bumper (it's the big oil cooler that runs across the front of the car, not the smaller one that fits in the LF fenderwell). Earlier this season, it had been leaking at the coupling to the oil line, and I had that fixed by having some custom washers made (the oil line comes into the cooler at a bit of an angle rather than straight in, hence the need for beveled washers). No problems after many track events.

Current theories:

1. Blockage in front oil cooler, causing pressure buildup. This would be consistent with having it happen when temps are cool, since the oil is more viscous and the pressures are higher. Note, however, that the oil pressure gauge was behaving normally.

2. Front oil cooler installation is such that it may be putting a pulling stress on one of the lines. On a bumpy track like Grattan, it might be eventually tugging the line out of the thermostat block.

3. Broken motor mount(s). Probably not - they're relatively new RS mounts, and the problem is in front of the thermostat block, not behind.

Has anyone had any similar problems? I'll post when I know more - the car is back home and in the shop for diagnosis.

Apologies to those who waited patiently while the track was cleaned.

Thanks.

Did you wait for the thermostat to open up before you went to full throttle/max revs?

Greg,

How would one know when the thermostat opens? Before going on the track, I always let the car idle for a while to begin warming up, but once on the track, I get into the throttle as hard as my cold tires and brakes allow me to.

The temp gauge will creep up to about the 9 oclock mark and then drop once it opens and lets oil up to the front coolers. My mechanic warned me not to go to redline or full throttle until this happened. Chris Cervelli also mentioned this in this thread : https://rennlist.com/forums/showpost...6&postcount=26

Will:

As the PO and the guy who installed the cooler, I would suspect a cause other than those you listed. Here is why...

1.) The oil cooler(s) are fed off a thermostat and have a bypass associated with it. If one or both of the coolers were blocked, it should not cause a massive pressure build up enough to blow a line. If it does, I would suspect the thermostat or the oil pressure bypass valve associated with the thermostat. Consider how the oil flows while the stat is closed.

2.) Also, I cannot see how this is being caused by bumps on the track causing the lines at the rear being tugged on as the lines are tied to the chassis in many places and all of these attachments would have to allow for the lines to slip in order for the rear line to be pulled out. The lines from the second oil cooler are simple extensions to the OEM lines no different than all of the other Cargraphic kits and have have not heard of any other failures like this. If they have, someone chime in !!!!

As another less techie possibility, did the wrench "top" off the oil after the first line pull out. If so, any chance of an over-fill???

FWIW, I would investigate the oil pressure relief and/or oil thermostat as culprits. $0.02

Sorry to hear of the oil mess...

Regards

The same thing happened to my friends cup car at watkins glen last fall. It is due to the low air temps. If the motor isn't warmed up the oil is too thick and this will happen. I think the little tab that holds the lines on is designed to bend under this high oil pressure situation. You could try a thinner oil, or easier would be to let it fully warm up before getting full on the throttle.

Pete

Great ideas, everyone. I knew I'd get some help from my fellow Rennlisters. :)

I'll definitely pass your suggestions along to my mechanic. Jim, you're suggestions are very helpful.

Regarding not warming up the car, I'm a bit mystified by that explanation. I start my car and let it idle for a while before gridding up, then of course it sits on the grid for a while with the engine on. Out on the track, I do get into the throttle pretty well, especially if there is traffic to consider, but so do my fellow 993 drivers, and I've never heard of a problem with their cars. None of them have the big Cargraphic cooler, so that's why I thought there may be a problem with it, especially since I had it worked on earlier this year and thought perhaps some contamination had occurred. Hmm....

Can overfilling really cause such a problem? My mechanic said that would not be the case. I guess I agree with him in my particular case, since the first time the line blew, I had checked the oil level and it was fine, right in the middle of the appropriate zone on the dipstick with the oil temperature at 180 degrees. Still, I'm curious about the consequences of overfilling - it's not hard to do.

At this point, I'm sorta favoring the "cold weather with insufficient warmup" scenario, with the differences between me and the other 993's being that I have a huge front oil cooler compared to them and perhaps need a longer warmup. Stay tuned!

Again, thanks to all.

Hey Will,

I thought I'd point out that both oil dumps happened in heavy braking zones during sharp, downhill turns (turn 3 and turn 10). I distinctly remember seeing the oil burst out of the lines as you were braking/turning into 10. I guess that's why I always thought it had something to do with tension on the lines.

Oh, and don't worry about dumping the oil. students were able to use the marks for turn in points for the rest of the weekend :)

what about the rear tire rubbing the oil line and "pulling" it out? I would think that could happen with extra wide rear wheels. Being at work, I cannot look at my car, so rubbing may not even be possible. Just a thought.

Jason, good point. Sorry about the oil all over your car - I'm just glad I didn't cause you to spin. Do you recall how long we had been out when this happened? I thought it was on the warmup lap, but it may have been the first hot lap.

Bob, good suggestion, but the oil line is not close enough to the wheel to cause a problem. Unlike my old '87 Carrera, they've moved the oil lines into pretty well protected areas.

Diagnosis still to come!

Will,
Think about what you are doing in the brake zone. You are most likely rev matching and that sudden blip may have caused the issue. Sounds like once the lines come off that you need to replace them?

Will,

It was probably the first or second hot lap when it happened in turn 10. That was Saturday morning when we all had the thick coating of frost on the cars, so it was pretty crisp out.

The incident in Turn 3 on Friday also happened on the 1st hot lap, didn't it?

Hmmm.

Jason,

The incident on Friday at turn 3 happened on the third lap - presumably when the car was nicely warmed up. I forgot I had it on tape! I'm just cruising along and the car just spins out, when I'm heard to say, "What the hell?"

:)

Like others have said, sounds like an over-pressure moment, especially since ambient was a little cool and this happened early in the session. You may want to replace the retaining bracket as it has more than likely been weakened from bending it back into shape.

Also, the oil line may have been pulled (or pushed) out half way on your outlap, not leaking oil until a lap or two later when the actual 'Valdez' occurred.

Tire rubbing on the hardline in the RR fenderwell is also something to look into as well.

Hi Will:

Greg offered some VERY sound advice about warming the car up properly before you lean on it. :)

Insufficient oil temps will do this and I highly recommend that you install an oil temp gauge that has temperature numbers on it, instead of those silly markings. (remember, the sender also must match the gauge)

You should have at least 185 deg F before you run the engine above 5000 RPM to prevent such occurrances as well as ensure that the oil is warm enough to lubricate the engine's internals properly.