oil leak on the intake side

jtower · 2011-03-06 11:20:50 UTC

i’m getting a non-trivial amount of oil leaking from the throttle position sensor on the bottom of the throttle body, which then drips down and makes a big mess on the left side of the motor. looks like it’s coming from the vent/breather hose at the top of the valve cover feeding into the side of the throttle body. what if anything can i do about this? replace the tps? plug the throttle body inlet and vent the valve cover hose to a catch can? install an inline separator of some sort? put a diaper on the tps? the airbox and throttle body are currently removed so i could clean things up.

FishMan · 2011-03-06 21:17:16 UTC

Blow by is causing increased pressure in your crank case and pushing oil to your intake through the breather hose. A catch may help, but freshening your bottom end is the proper fix.

jlevie · 2011-03-07 00:13:18 UTC

Excessive oil in the intake will be from worn rings. worn valve seals, or a combination of those. Compression (dry and wet) and a leak down test will tell a lot about condition of the rings.

There was a big discussion a couple of years ago about catch tanks. As I recall the consensus was that a catch tank would not be a legal mod. In my opinion a catch tank should be allowed as it provides no competitive advantage and makes it easier to live with a worn engine (thus cheaper).

jtower · 2011-03-07 06:21:47 UTC

my engine was built in 2009 by someone who ostensibly knows what he’s doing and it makes pretty good power (as everyone is fond of reminding me). so i’d say it’s reasonably unlikely, although not impossible, the rings are problematic.

what would happen if i clamped the breather hose shut? that would solve the intake oil leak but presumably something even worse would result.

three possibilities off the top of my head (no pun intended):

i’m getting excessive oil thru the breather, root cause TBD
i’m getting a normal amount of oil thru the breather but it’s leaking out the TPS, which is atypical
i’m getting a normal amount of oil thru the breather but it’s leaking out the TPS, everyone’s car does this but no one whines about it

Ranger · 2011-03-07 07:12:43 UTC

Have to have the vent or the engine’s seals won’t last because the inside of the block will be a high pressure zone.

How much oil are we talking about?

The seal between cylinder wall and ring usually last quite awhile on our motors. Most everyone who pulls apart a high mileage motor remarks how they can still see honing marks on the cylinder walls. The way you lose bottom end compression, apparently, on a race motor is the ring grooves in our cast pistons get hammered out. That allows the rings to move a bit more than they should, and a consequence of that is more blow by. And none of this should apply to a relativelyl fresh bottom end.

jtower · 2011-03-07 12:10:06 UTC

[quote=“Ranger” post=55001]Have to have the vent or the engine’s seals won’t last because the inside of the block will be a high pressure zone.

How much oil are we talking about?[/quote]

it’s not a ton of oil but enough to make a bit of a mess. i’m kinda fussy about fluid leaks, after each weekend i put the car on jacks and wipe down everything that looks wet, this is always the first place i hit with the rags.

isn’t there a vertical tube between the crankcase and the bottom of the intake manifold? does that vent or serve a different function than the rocker cover breather?

jlevie · 2011-03-07 22:37:32 UTC

[quote=“jtower” post=55010]it’s not a ton of oil but enough to make a bit of a mess. i’m kinda fussy about fluid leaks, after each weekend i put the car on jacks and wipe down everything that looks wet, this is always the first place i hit with the rags.

isn’t there a vertical tube between the crankcase and the bottom of the intake manifold? does that vent or serve a different function than the rocker cover breather?[/quote]
A slight film of oil in the intake is normal on these engines, but enough to drip out of the TPS is abnormal. As an FYI, the TPS is normally sealed, but a builder who knows his stuff will drill a small hole in the bottom of the TPS. Otherwise oil will collect in the TPS and cause it to fail.

The tube under the intake is the oil return from the head. Although it connects to the intake manifold that connection only goes into the head, not into the intake.

[quote]1. i’m getting excessive oil thru the breather, root cause TBD
2. i’m getting a normal amount of oil thru the breather but it’s leaking out the TPS, which is atypical
3. i’m getting a normal amount of oil thru the breather but it’s leaking out the TPS, everyone’s car does this but no one whines about it[/quote]
Option 1

An engine built in 09 should not have this much oil in the intake. The question now is whether it is from the valves or rings. Compression and leakdown tests should help assess the cause.

Ranger · 2011-03-07 23:26:34 UTC

Re. oil return. I think that the bitch tube doesn’t normally return oil to the block. Pop the rocker arm cover off and look down at the contours of the head. Look at the oil return holes that parallel the head bolt holes, and than look at how the oil would have to flow to get to the bitch tube. I think you’ll see that the oil will preferentially go down the vertical holes.

I’m not saying it doesn’t go down the tube at all, but look at those oil return holes and you’ll see what I’m saying.

tpr_jules · 2011-03-08 03:45:26 UTC

Jason, one more theory - and this is the one that I subscribe to as our 919 car has the same issue. I discussed with David and Vince at Harrison Motorsports (they help us a bunch) and they said that this is a common issue with M20’s when cornered hard. Oil flows up from the valve cover vent/breather tube during high G turns. This is less of an issue when I drive the 919 but Eric has also driven it so that makes more sense In any event, if you haven’t checked that for a while, you prolly had a bunch of oil accumulation and it finally went into the TPS. I clean ours out every couple of events. Clean up and monitor after every event. Hope this helps.

turbo329is · 2011-08-30 02:09:12 UTC

[quote=“jlevie” post=54985]Excessive oil in the intake will be from worn rings. worn valve seals, or a combination of those. Compression (dry and wet) and a leak down test will tell a lot about condition of the rings.

There was a big discussion a couple of years ago about catch tanks. As I recall the consensus was that a catch tank would not be a legal mod. In my opinion a catch tank should be allowed as it provides no competitive advantage and makes it easier to live with a worn engine (thus cheaper).[/quote]

can we get this in the rulebook for 2012 since i,ve already done it. My engine is thoroughly worn.

jlevie · 2011-08-30 02:59:57 UTC

[quote=“turbo329is” post=59487][quote=“jlevie” post=54985]Excessive oil in the intake will be from worn rings. worn valve seals, or a combination of those. Compression (dry and wet) and a leak down test will tell a lot about condition of the rings.

There was a big discussion a couple of years ago about catch tanks. As I recall the consensus was that a catch tank would not be a legal mod. In my opinion a catch tank should be allowed as it provides no competitive advantage and makes it easier to live with a worn engine (thus cheaper).[/quote]

can we get this in the rulebook for 2012 since i,ve already done it. My engine is thoroughly worn.[/quote]
I certainly favor a rule change to specifically allow a catch tank. It helps reduce plug fouling on a high mileage engine, and so far as I can tell has no affect on a low mileage engine.

This is a slightly gray area in that 8.10.1 mandates a catch tank if the oil breather is vented to the atmosphere, but no where else in the rules does it say that modification of the oil breather system is permitted (the “if it doesn’t say you can, then you can’t” rule).