Odd oil leak under extreme load... only..

[JimRummy]

Good evening friends. So over this last week I went camping at Lake Cachuma in central/southern CA with my Girlfriend, Daughter and buddy. If you're not familiar with the area, it is right past Santa Barbara, about 30 miles up east into the mountains, and it was 104 degrees the entire way. From my house it is about a 140 mile drive with 105 being freeway, and the last 35 miles being up mountainous large 7%+ grades. With about 18 miles left going up a large part of the grade (and going about 75 because I was passing someone who wanted to go 15 under the speed limit {and these are the situations that would cause my truck to overheat in the past} and I had 2 vehicles following me, so I had to go fast) my truck developed a decent sized oil leak.. Like I was billowing some pretty large clouds of smoke under my truck. I pulled over, turned off the engine, and the smoking slowed down and eventually stopped. We were close to the campsite (16 or so miles), so we pressed on. After another minute or so it started up again while going up the grade, and I pulled over at a ranger station (haha). There was a oil trail behind me, not quite a complete line, but almost, and the oil was running out like it had thinned out considerably. We were there with the truck off for maybe 10 minutes before we left, and there was a 8" diameter spot of oil I left on the ground.
Here is where it gets really strange. After leaving the ranger station there was still hills, but now it was mostly downhill or level. I took the bike rack off and put it on my buddies truck and we headed off. 15 miles later (with some hills) got to the campgrounds, and pulled over before checking in (waiting for the last person who got separated to arrive), and there is no oil trail. No leaking whatsoever. 5 minutes goes by, not a drop. Drove it to the campsite, and around the campsite all week. Not a drop.
Finally Yesterday (and with extreme worry and anxiety all week) I did the 140 mile drive home, again 103 degrees ( going 65-75 ). Again not a drop of oil lost. Check the dipstick again today, oil level is fine, nothing on the ground, no clear oil leaking at all.
I'm really stumped. I haven't gotten a chance to really dig in yet, but I wanted to get some opinions so I have an idea of what to look for. Don't want to open a can of worms, but I don't have the money to ignore it either.
A little history on the truck; It has never leaked oil before. Maybe a tiny bit of seeping you could see under there, but not actual leaks. No real formed droplets. and never any on the ground. Only coolant before head gasket job
The truck is a 1993 4.0 AT, and had a head gasket job about 12,000 miles ago. I run 10W-30 Synthetic (I've heard of synthetic getting past older engines seals, don't know if that was the case)
It has 133,000 miles on it, and everything is original with the exception of replacing the coil pack & MAF (both stock motor craft) and I'm good with keeping all fluids fresh.
The only modifications it has besides audio stuff is it has a KKM intake, Flowmaster 40, 225 75 15 Toyo Open Country AT 3 -15x8 Outlaw II (came with the 14x6 wheels) & the dual piston upgrade from a 96 Explorer.
I had about 270 lbs in people weight, about 100 lbs in the tool box, 200 lbs in the bed, and then the bike rack (which was really heavy duty) and bikes were probably 70-80 lbs altogether.
So around 640 pounds of extra weight between the cab, bed and trailer hitch.
Like it said I was going fast, up a large grade in 103 degree temperatures, but why would it go away? Then not come back when coming home in slightly less harsh conditions (less up hill), but still pretty rough...
I never got any check engine, or needles jumping and the truck never acted strange. No weird shifting or noises, lack of throttle or anything...
ANY input, as always is greatly appreciated.

 

[RonD]

Check its hoses and change PCV Valve

You probably have a small oil pan or valve cover gasket leak, I am trusting you that its not an Automatic trans cooler line leak, because you would have checked that.................

When engine is under a load Blow-by goes very high, so pressure inside the oil pan and valve covers also goes high........UNLESS PCV valve can keep up
But under load vacuum also goes down a bit so unless PCV valve is in tip top flow condition the pressure inside these areas PUSHES oil out of small leak points, so they are no longer small leaks, lol

Once pressure is gone, lower blow-by, then you are back to the smaller gravity leaks

 

[JimRummy]

Check its hoses and change PCV Valve

You probably have a small oil pan or valve cover gasket leak, I am trusting you that its not an Automatic trans cooler line leak, because you would have checked that.................

When engine is under a load Blow-by goes very high, so pressure inside the oil pan and valve covers also goes high........UNLESS PCV valve can keep up
But under load vacuum also goes down a bit so unless PCV valve is in tip top flow condition the pressure inside these areas PUSHES oil out of small leak points, so they are no longer small leaks, lol

Once pressure is gone, lower blow-by, then you are back to the smaller gravity leaks

I'll do that. I've never replaced the pcv, and at 27 years old I'm sure it could use it either way. Thanks for the quick reply.

 

[Dirtman]

It was due to be changed 26 years ago...

 

[JimRummy]

It was due to be changed 26 years ago...

Yeah after discussing it with a few people I've heard of many that change it yearly. What can I say, if it ain't broke don't fix it. Never had a problem before, and getting 18/20 mpg I had no reason to go searching for problems that didn't exist.

 

[Dirtman]

"If it ain't broke don't fix it" doesn't apply to routine maintenance...

I'm not trying to bust on you here but the PCV valve is a maintenance item that needs to be replaced often. It keeps pressure from building in the crankcase which prevents leaks as you now know, but when it starts to fail it also reverses the flow of those crankcase gases sending them through the intake tube and throttle body where they build up carbon and cause performance issues.

You don't wait until your engine seizes to change your oil, and you don't wait until your engine is puking oil to replace the PCV valve.

 

[JimRummy]

"If it ain't broke don't fix it" doesn't apply to routine maintenance...

I'm not trying to bust on you here but the PCV valve is a maintenance item that needs to be replaced often. It keeps pressure from building in the crankcase which prevents leaks as you now know, but when it starts to fail it also reverses the flow of those crankcase gases sending them through the intake tube and throttle body where they build up carbon and cause performance issues.

You don't wait until your engine seizes to change your oil, and you don't wait until your engine is puking oil to replace the PCV valve.

You're right, I would never argue against preventive maintenance. It's the reason the truck is still on the road. I just checked and the maintenance schedule says every 60k, so this should be at least the second replacement, if not third or fourth. There's definitely some things that get ignored, like some of the lubrication schedules. 7,500 for U joints, steering linkage & drive shaft.. I can't say I've done those that often..

 

[RonD]

I change PCV valve when I change fuel filter, every 5 years or so, lol

But each engine type is different, so its not a fixed interval for all, many change it at 3rd oil change, so for some that might be once a year for others once every 2 years

 

[Dirtman]

My theory is if its simple to get to, just pop it off and clean it with some brake cleaner every oil change. Do that and itll last quite a while, but its also only a 5 dollar part so no point to not just toss a new one on every few years.

Now on my truck, it is a horrible pain in the ass to remove. The wheel and inner fender need to be come off just to get near it. So I admittedly often let it go a little longer than I should. I usually end up doing it when I do brakes since I'm already in there...

 

[JimRummy]

My theory is if its simple to get to, just pop it off and clean it with some brake cleaner every oil change. Do that and itll last quite a while, but its also only a 5 dollar part so no point to not just toss a new one on every few years.

Now on my truck, it is a horrible pain in the ass to remove. The wheel and inner fender need to be come off just to get near it. So I admittedly often let it go a little longer than I should. I usually end up doing it when I do brakes since I'm already in there...

Good advice. Never had a problem so it was never on my mind. It's on my radar now, among the other routine maintenance parts I've been slacking on. The lubing of the suspension & joints is the only thing (aside from the pcv) I haven't be as on top of as I should be.