Forged pistons and oil consumption

[75Carrera]

Since upgrading my 75 Carrera's motor with a sweet '88 SC 3.2 (see description below) I've been experiencing unusual oil consumption. This is my first experience with "ROSS" racing pistons. I finally called Ross to see what they could tell me about the high oil usage. I was already aware that forged pistons need to warm up before expanding to seal the rings in the barrels but assumed that would be compensated for by added warm-up time. I've placed blankets over my intake grill, let her idle in the driveway for 15 minutes (or longer) but the oil usage remained unreasonably high.
When we installed the motor we also added a 28-29 bar front fender oil cooler but kept all my 2.7 lines otherwise (no cat). The car seldom warms up beyond 130 degrees (even after some spirited runs) and has yet to see 180. I suspect the problem is the pistons aren't running warm enough to properly expand and seal the rings completely. I even tried wrapping the cooler bars with an insulated piece of sound damper material (no change). Now I believe the issue is my oil thermostats, either at the motor or at the return line. If they aren't working properly (question here) could that be the problem? Ross said "as long as I don't mind pouring oil through the motor it isn't hurting the car" I'm not too sure about that but the idea of running warmer to allow the pistons to properly expand does make sense. Anybody out there know more about forged piston operation temps or have an opinion about this issue?

[DUK]

Did they recommend using any detergent oil to help seat the rings? We used to send a pint of sea-foam with the vw engines for break-in and never had any problems after that.

Just my .02

[75Carrera]

Actually my wrench filled her up with synthetic (which I dumped after about 1000 break-in miles and switched to a semi and then went to a straight Dino 15/30) Operating temp seems an obvious issue...
What's "sea-foam" Duke?

BTW: Duke, did you guys notice MID9 is down? Looking for someone to take over the site and get us back up. Any ideas there? PM me if you'd like to know more about that.

[DUK]

Break-in on synthetic is a bad idea. Ask lubemaster or the others, I'm sure they can explain it better than me.

Sea-foam is a detergent additive for oil. Helps the rings "cut" and seal.

PS- I haven't been on the mid9 site in quite a while. I'll let a few others know though.

[YTNUKLR]

The Mahle 4000-series Aluminum (I think 4024), original equipment (OEM) is a high-silicone alloy which makes it weaker than the same part made from 2618, which is what JE and Ross pistons are made from. These aftermarket pistons have more copper and less silicone, are stronger than 4000-series parts, but expand and contract much more with temperature changes.

The oil temperature is very important. The engine needs to see 180 F/82 C. The problem sounds like your thermostats for sure, I would definitely check/replace them, or add the one to the front cooler if you don't have it yet. Try putting a blanket around the front cooler on especially cold days.

Otherwise, your issues may be related to set-up. Using cylinders that were in-spec. and not out of round is very important. Then, pistons must have been sized correctly for your application, in order to achieve proper piston/cylinder clearance. With Nikasil cylinders and JE pistons (Ross, same deal), I like .0015" clearance, perhaps as little as .0013" if using dry-film lubricants and/or putting them in a street car. Less clearance=less oil consumption.

Oil consumption is not a good thing, but it WON'T hurt the car. Oil just seeps by and burns. May cause unpleasant exhaust scent and cause you to spend a few bucks topping up the oil.

Should break in a fresh motor (new rings, or in storage for prolonged period of time) with a non-detergent mineral oil, NOT synthetic because it is *too* slick and does not generate enough friction to seat the rings. I have never personally used Sea-Foam. Should beat on it to get the rings to seat, ie., lots of 3/4 throttle and deceleration in gear (no/less brakes) as soon as the engine is at operating temperature.

Get the thing up to temp.!

Cheers,
Scott

[75Carrera]

Scott,

Excellent pin-point evaluation and advice my friend. My wrench is a top air cooled hand and mind. He felt the fresh, tight motor would break in just fine but early smokey traces took me back for a switch to a semi. Considering it's "all about the oil temp" (to which I agree), my wrench wasn't wrong. Even on straight dino there's no real difference. The oil temp stayed at the 120-30 level constantly so the piston never expanded to close her up. I looked on a few sites for new thermostats ($3-400) ugh!

No problem putting the juice to my motor! LOL I live in "twistie heaven" with no real traffic, so running at high RPM (once I get this thermostat thing worked out), using the motor and no more than tap brakes up and down the mountain sides of Northern Arizona to test the results will be a chore but, hell, I'll do it!

Thanks Scott.