911SC engine troubles...Overheat and oil leak?

cnielsen · 05-14-2009, 10:31 PM

Quick facts...

Built this car for my dad...'69 chassis, '79 3.0L with only 40K original miles on the motor. Details of the swap here....

Refreshing a 1969 911T / RS

No major work done to the motor. Recent valve adj and slight advance of cam timing prior to install into the '69. Back dated heat and exhaust. Front oil cooler (loop) and trans also from the '79 installed in the '69 chassis. CIS airbox was cracked but repaired. Also installed the enhanced sump screen available from EBS.

History of problem...

On a recent road trip we noticed the oil level was low. Strange as it had just been changed. Suspected that oil went into the new oil cooler lines and was now showing low on the dip stick. Added oil and proceeded. 45 min or so later we discovered an over heating issue, going down the freeway at 70mph, ambient temps at 60 deg. Engint temps started climbing to 250. Pulled over, looked everything over. Engine was definately hot. Hotter than other cars in similar situation. Oil cooler lines were hot also...not warm but pretty hot. Oil was also leaking out of the rear main seal area and dripping out the bottom of the engine yoke (rear motor mount support). BTW, oil pressure guage is normal and shows very good pressure.

We let the car cool down and attempted to drive again. Sure enough, same thing 5-10 min later...stopped the car and had it trailered home.

Current status...

Drained the oil, found nothing suspicious although, I did save some oil and sending out for analysis. They will determine if there are any particulates and if so, what they consist of. All oil lines seem fine, non are collapsed. Pulled the alt fan off, inspected the top of the motor and top of the engine oil cooler...everything looks good and clean. Alt belt was tight and fan was functioning properly. Also inspected installation of sump screen but the new EBS sump screen can only be installed one way and it is correct.

Added new oil/filter and started the car. Everything seems fine. Let it run for 45 min in the garage and still nothing unusual...temps are stone cold, motor runs smooth, revs smooth...totally normal. All guages read normal. Tried spraying carb cleaner around the CIS box where it was cracked and did not notice any variation in idle. Also, NO oil leaks at all while it was running.

No oil leaks over night either...bone dry.

Drove the car to work this morning (3 miles) and all seemed perfectly normal. Ran great, lots of power, revs nicely. Looked under the car and still bone dry.

Drove the car on an errand at lunch time (45 min round trip), tried to drive it hard...higher revs etc to build temps. Ran great up until about 5 mins from my office. Temps had stayed constant at below 180 but now they started slowly climbing to about 190 and then dropped again. I figured that is when the front oil cooler kicked in. Still ran smooth but noticed a hint of oil smell. Finished driving back to the office with stable temps.

When I got in the parking lot, I noticed the car started to stumble like it was missing a cylinder. Also noted an oil "bread crumb trail" through the parking lot. A decent sized drip every 12 feet or so. Looked under the motor and it was leaking again through the rear main seal area.

Came out after work (several hours later) and there was no further oil leaking from the motor...only that which had leaked when I pulled in. Started fine, ran great all the way home with no issues (3 miles). No leaks when I pulled in the garage.

Ideas...

1. Initially I thought something had obstruced the engine oil cooler so air was not getting to it...totally clean, nothing there.

2. suspected overfill on the oil level as we had added several qts at the road trip stop...counted qts removed from the engine and seemed normal. Also read correctly on the dip stick. That means the engine was low on the road trip. If it was leaking then the way it is now, I am not surprised.

3. Will have oil checked for any particulates causing internal friction. Doesn't make sense though as it runs GREAT at operating temps of less than 180.

4. Air fuel mixture problem? Just had that checked at idle a short while back. Although I just ordered a portable A/F meter so I can check it while driving. If the air box is causing an air leak that for some reason is temp related, then it would run lean and could potentially cause an overheat....but how does the oil leak relate to that?

5. Plain out of ideas from here...

HELP!?!?

Anyone got any brilliant ideas before I do something crazy like buy dad a Japanese car

sc_rufctr · 11:22 PM

Your symptoms trouble me...

I have no real idea of what it could be but I would double check the ignition to
make sure it's not "Over Advancing" at higher RPM. (Check with strobe light at 6000rpm)

I'm guessing you've already checked the ignition but thought I should post it anyway.

Brother · 05-15-2009, 12:23 AM

Stock oil pump?

I'm going through the irrational options and started thinking about the pickups not emptying the case at some random times. This might cause a leak and a lack of cooling which then returns when the flow returns to normal.

Elombard · 05-15-2009, 02:44 AM

I had an SC engine over pressure and start leaking once when I capped off the breather to the back of the CIS "turtle" and then inadvertently pinched the breather hose from the top of the motor to the oil tank before installing a catch tank with a breather. Apparently quite a bit of pressure develops inside the case and it is normally vented into the intake.

Not sure if this would lead to an over heat but it caused weird oil leaks like crazy.

Bill Verburg · Bill Verburg's Garage

Sounds like the oil could be going into the crankcase as described here, that was an issue w/ '78 SCs.

You mentioned a new sump screen, are you sure that is installed correctly?

cnielsen · 05-15-2009, 05:48 AM

Thanks for the input guys! It makes me feel better now that we have some collective thought going into this. I'll try and answer some questions...

Sump screen... The new updated one from EBS can only go in one way. I confirmed this with a call to EBS and spoke to Troy.

Timing... That was checked when the motor was first installed, probably 250 miles before the problems started showing up. My mechanic checked it and I always see him do an idle, then a high RPM so I would assume it is still good.

Ignition... All stock SC components

Oil pump... Also stock SC

Breather tube...Now I find this idea interesting. I did try and "simplify" the SC motor as much as possible. Got rid of all the emissions stuff, basically tried to backdate it to a '74 type setup. One thing I did notice is that the hose going into the airbox breather had a mesh restrictor in it. I replaced it with a plain rubber hose. i.e. no restrictor. Would the lack of that restrictor cause and air issue where it would cause the oil to stay inside the crank case, over pressuring it more or less...leading to leaks and high temps??? Sure would be an easy fix

dtw · 05-15-2009, 06:15 AM

Gorgeous preparation. Nice job!

Some thoughts in no particular order -
-First thing that sprang to mind is that you overfilled - have you verified oil level correctly?
-Is crankcase breather line kinked? Are you sure that the leak is coming from the flywheel seal, or could it be leaking down from the (blocked?) breather line?
-With the engine warm & idling and the airbox lid & filter pulled, are you getting air flow from the breather vent line? Any oil smoke into the airbox from the breather vent line?
-Put a timing light on the engine again
-What kind of shape are the valve guides in? Done a leakdown lately?
-Have both thermostats been checked out (cooler lines get hot though...huh...)
-Cracked airbox - repair might be stable at idle but letting air in under higher vacuum/load conditions
-What does the plug cut tell you?

You should probably order those questions better than I did, but basically they are looking for evidence that the engine is leaning out, and/or that the heads/valves are not doing their job of helping cool the engine. Start with the overfill though, that's the low-hanging fruit.

cnielsen · 05-15-2009, 06:27 AM

1. checked, double checked and triple checked the oil level. Not overfilled.

2. Crank case breather does not appear to be kinked. Pretty much a straight shot from the tank to the breather.

3. No smoke in the airbox

4. Oil leak is coming from the rear main seal...back of the motor...not the flywheel side.

5. Both T-stats appear to be working as both coolers get hot.

6. I wonder about the air box too... but it would have to be temp related as it runs great under load when it is cold...or at least not HOT.

7. What is a plug cut?

8. If the oil tank were getting too much air in it or letting too much air out...i.e. no restrictor, would that cause a problem?

mca · 05-15-2009, 06:34 AM

Could it be your that your oil cooler needs to be pressure tested?

If it were to leak then it would look similar to an RMS leak.

cnielsen · 05-15-2009, 06:38 AM

The oil leak is coming from the back of the motor...not the front. Its back by the rear motor mount yoke...near the muffler.

john walker's workshop · 05-15-2009, 06:40 AM

SCs are a closed crankcase system. you have the breather hose from the filler neck going to the side of the airbox instead of to the back of the air boot. that may cause some difference in how much the sensor plate raises in relation to throttle opening. ever notice how SCs run funny when the oil cap is off?

mca · 05-15-2009, 06:41 AM

Quote:

Originally Posted by cnielsen

The oil leak is coming from the back of the motor...not the front. Its back by the rear motor mount yoke...near the muffler.

Ok... earlier you said RMS which is at the front of the engine (flywheel side).

Hmmm. So is it coming from the #8 nose bearing area?

dtw · 05-15-2009, 06:43 AM

I was thinking that screen was to help precipitate oil droplets but could be totally wrong.

Oil leak - oops, I was thinking flywheel seal. Thought that was the RMS. Anyway, well damn, that's scary. Hopefully the o-ring on the crank nose bearing is not damaged.

Airbox - a small unmetered air leak under load might not show up on the butt dyno - it could just slowly roast the motor until you ran into the overheating conditions you mentioned. Had similar problems on my 2.7 pre-rebuild, but it was caused by other factors. However, 30 mins of normal driving in 60 degree weather would have my temp gauge over 250. I also ran into stumbling and oil leaks just like you describe when the temps got that hot.

Plug cut - the process of 'reading' the spark plugs - search here or on the googles for detailed procedure. Can help to tell you if your combustion chambers are getting oiled or if they are running too lean. Post good-quality macro pics here if you are having trouble reading them.

Elombard · 05-15-2009, 07:39 AM

Thats it I think.

If you are running from the air box to the oil filler neck and the breather at the top of the motor next to the throttle lever mount plate is capped; when the oil is in the tank it would cause the block to be under pressure?

Or where does the hose from the top of the block go to? Capped (as I speculate above) or teed in?

That mesh thing I think is just to keep oil from slopping into the intake.

daepp · 05-15-2009, 08:09 AM

Can breather issues cause 250+ deg engine temps?

My thought is oil blockage causing excess engine heat and the resultant leak @ #8.

Stuck thermostat? Clog?

Elombard · 05-15-2009, 08:55 AM

Good point David, seems odd that it would not start the symptoms though until after a while? Maybe the stuck thermostat does not come into play until its warm?

cnielsen · 05-15-2009, 09:06 AM

Thanks a ton for the input!!!!

Ok, so my plan is to reconfigure the breather line to the correct location AND check the air fuel ratio coming out of the exhaust. I am assuming that would help me determine if there was a crack in the airbox that was causing a lean situation.

John W, I think you are right. This car does not run any different when the oil cap is off so I would assume there is an issue with the breather.

Sound like a good plan?

Anyone have a 78-79 good CIS airbox laying around?

Elombard · 05-15-2009, 11:13 AM

Try rubber banding a rag over the oil cap opening (leave cap off) and drive around and see what it does?

I am very curious.

SP2 · 05-15-2009, 11:57 AM

But what about the oil leak?

cnielsen · 05-15-2009, 12:08 PM

I think the oil leak is caused when the case heats up and has too much oil in it...not overfilled, just too much in the case and not enough in the tank. Also too much oil in the case would make the motor work too hard and potentially cause an over heat issue.

I have heard from several sources that symptoms of an overfill are; increase in engine temps, oil in the air box and leaking crank seals. All of which resolve when the overfill is corrected. We basically have the same symptoms but it is being caused by something else.

Not sure if leaving the cap off would do anything as the filler neck is vented into the air box at the air filter. Soooo, it is not a sealed system as John Walker stated that it should be. I think I need to route the oil tank vent back where it was supposed to originally go....onto some emission crap that I was tyring to eliminate.

Anyone have any photos of the back of a stock SC motor showing the configuration of the hoses?