Oil Blow-By Diagnostics/Engine Swap or Rebuild

[tonytony9]

Hi Everyone,

I have been trying to chase down a pretty massive oil leak on my Stock 302 (to the best of my knowledge original to the vehicle) for some time now. I redid the 2-piece Rear Main Seal, Oil Pan Gasket, Intake Manifold gasket, Valve Cover gasket. Rebuilt my AutoLite 2100 carb with a very knowledge old schooler. Used all Fel-Pro gaskets following guides on the forums. My compression is very solid/consistent. Leak-down test on cylinder 1 was not good. I replaced all my vacuum lines, PCV valve, Distributer dual port vacuum advance, and Oil Fill Cap. I am loosing about 1-quart per ~100 miles. It is dumping on the ground. The bottom of the Bronco looks like a war zone. I have cleaned it up, tried to trace it down, I cannot figure it out.

For the most part, the motor runs and idles very well. Has never left me stranded. I have oil building up all over the intake below the carburetor. I am getting a good amount of oil in the stock air cleaner. No smoke out the exhaust. During the leak-down test, yes it was at TDC, I could hear air coming from the top of Carb (intake valve?) and through the dip-stick tube. None from the exhaust pipe. I am going to re-run the test this week on every cylinder and post a video. I thought this might had been from washing out the rings because my old carb was running way too rich. So I rebuilt, and put another 1,000 miles on it.

Questions:
1. Are there any more tests I can run to try and confirm this is Blow-By and pin-point where it is coming from: Valve stem, Piston Ring, Head Gasket, Block Damage?
2. If my leak down test does fail again, what should I be considering in a cost-effective motor? I want more HP and pep then stock. NO EFI! Need a bit of reliability I love driving the Bronco on longer runs. Explorer 5.0? Rebuild? If the Valve Stems are shot, buy a rebuilt GT40 head to drop on? I would really like to avoid buying a new motor if possible. Heard Summit ATK Roller 5.0 fully dressed is the cheapest best option.

Cylinder Compression:
1. 150
2. 145
3. 140
4. 150
5. 150
6. 148
7. 148
8. 148


Leak Down Test Video:
YouTube - Leak Down Test

Block Tags:

PCV Setup:

Misc:

 

[AZ73]

Blowby is rings or scored cylinder walls ( they can get the oil washed off them with excessive fuel and no spark while the engine is turning over and the rings scratch the walls). If it's bad you'll see smoke coming out of the valve cover at the pvc hole when you pull the pcv out.

Just do a leak down test on each cylinder making sure the valves are closed at that cylinder. Usually if it's bad it will escape through the oil dipstick or the valve cover gaskets. Sometimes though the oil pan gasket. Leakdown is rings or valves, but you wouldn't really get blowby though the valves.

1 qt per 100 miles is an awful lot for blowby. What's your oil pressure? I once has a tiny crack in the block righ at an oil passage, but it was on the inside of the engine so the oil ran back into the pan.

 

[Timmy390]

I am loosing about 1-quart per ~100 miles. It is dumping on the ground. The bottom of the Bronco looks like a war zone. I have cleaned it up, tried to trace it down, I cannot figure it out.

Oil pan gasket, rear intake manifold gasket i.e. rear china wall, valve cover gaskets, distributor gasket and rear main would be the first place to look.

Clean it up the best you can then go to local parts store and get the dye to add to the oil. Run the engine then use black light to find the source of the leak.

Tim

 

[Wild horse 75]

While not common I have had head gaskets fail in such a way that they leak oil like a sieve. It will run down the seam between the head and block and look like it’s the intake but it isn’t. I would also look at resealing your oil pressure sender and fuel pump. The pump itself can also leak oil.

 

[DirtDonk]

Another common source of a leak “down low “is from the rear corners of the valve covers. So check those very well for any oil seeping out of the back. That can easily travel down low and look like it’s a leak from elsewhere.

 

[tonytony9]

Blowby is rings or scored cylinder walls ( they can get the oil washed off them with excessive fuel and no spark while the engine is turning over and the rings scratch the walls). If it's bad you'll see smoke coming out of the valve cover at the pvc hole when you pull the pcv out.

Just do a leak down test on each cylinder making sure the valves are closed at that cylinder. Usually if it's bad it will escape through the oil dipstick or the valve cover gaskets. Sometimes though the oil pan gasket. Leakdown is rings or valves, but you wouldn't really get blowby though the valves.

1 qt per 100 miles is an awful lot for blowby. What's your oil pressure? I once has a tiny crack in the block righ at an oil passage, but it was on the inside of the engine so the oil ran back into the pan.

The oil loss cant just be from Oil Blow by. But maybe the extra crankcase pressure blew out the RMS??

Last leakdown the air was coming through the oil dip stick and the top of the carb as in the video

Cylinder Compression:
1. 150
2. 145
3. 140
4. 150
5. 150
6. 148
7. 148
8. 148

 

[Brush Hog]

I’m with Dirt Donk. Those valve covers look a bit weathered. I had a bad leak I chased for about a year. Ditched my beat up thin stamped aluminum valve covers for some more ridged cast aluminum covers and problem solved. Ridged edge better seal don’t bend like the stamped ones.

 

[73azbronco]

Old motor? Bet valve guides/seals.

 

[.94 OR]

If you are getting air escaping back up through the carb I would suspect a burnt valve but your compression numbers don't really show that.

 

[BOBS 2 68S]

I chassed oil consumption and had to install a baffle under the PCV also replaced the new PCV with another new unit. Is your oil pressure sender extension pipe loose? Is you oil fill/ breather clogged with oil and dirt?

 

[tonytony9]

Another common source of a leak “down low “is from the rear corners of the valve covers. So check those very well for any oil seeping out of the back. That can easily travel down low and look like it’s a leak from elsewhere.

I’m with Dirt Donk. Those valve covers look a bit weathered. I had a bad leak I chased for about a year. Ditched my beat up thin stamped aluminum valve covers for some more ridged cast aluminum covers and problem solved. Ridged edge better seal don’t bend like the stamped ones.

I chassed oil consumption and had to install a baffle under the PCV also replaced the new PCV with another new unit. Is your oil pressure sender extension pipe loose? Is you oil fill/ breather clogged with oil and dirt?

Ok, two issues I am dealing with; potential oil blow by and loosing a ton of oil on the ground.

The valve covers, I will clean up, use the dye, and run to see if I can see oil leaking from there. If so, I will buy new valve covers. Any suggestions?

I am also going to test the PCV to see if there is a noticeable idle change when removed/putting my finger on the bottom to plug it. If not noticeable change, replace PCV?

Could an improper PCV setup and/or clogged/broken PCV/Oil cap be also contributing to the oil mess? Even contributing to oil blow by?

What PCV, Oil Cap and Valve covers should I buy? I am currently routing the Oil Cap Breather to my original Oil Filter housing (stock ford one).

 

[laserfish]

Had a friend with 78 F150 302 that leaked like a seive 30 years ago. I finally figured it out. The line from the carb base to the PCV valve was clogged. Everything looked good from the outside but there was no crankcase relief. Add that to the fact it was well worn and it built up pressure enough pressure in the crankcase to push oil out of every weak seal. Check that PCV and make sure it has good vaccuum.

 

[DirtDonk]

Same thing here. A friend had a 76 LTD that I was giving a tuneup to one time. Noticed the PCV was acting funny and found that the original hose and hard line were completely caked up with burned up oil. Or I should say “coked up“ instead.
A little bit of soaking with B12 Chemtool, and a little poking with whatever chaser tools I had around, and finally the gunk broke up and spit out.
Everything worked great after that!

 

[tonytony9]

Had a friend with 78 F150 302 that leaked like a seive 30 years ago. I finally figured it out. The line from the carb base to the PCV valve was clogged. Everything looked good from the outside but there was no crankcase relief. Add that to the fact it was well worn and it built up pressure enough pressure in the crankcase to push oil out of every weak seal. Check that PCV and make sure it has good vaccuum.

Same thing here. A friend had a 76 LTD that I was giving a tuneup to one time. Noticed the PCV was acting funny and found that the original hose and hard line were completely caked up with burned up oil. Or I should say “coked up“ instead.
A little bit of soaking with B12 Chemtool, and a little poking with whatever chaser tools I had around, and finally the gunk broke up and spit out.
Everything worked great after that!

I am hoping this is my issue! Running diagnostics today and I will report back with a video. Thank you everyone!

 

[tonytony9]

I am hoping this is my issue! Running diagnostics today and I will report back with a video. Thank you everyone!

Okay, I confirmed that my PCV tube is not blocked. Blew air through the line, it is clear. Pulled out of the valve cover, covered with my finger, noticed great suction and the idle dropped.

Can someone please confirm my vacuum system is correctly hooked up? I have a hunch the blow by is caused by my valve seals, some sort of issue on the intake side. But still need to confirm with wet compression test and closer diagnostics on the leak down side.

 

[DirtDonk]

Someone (I think it was Oldtimer) recently posted a diagram of the vacuum cone thingy.
I could be wrong, but it seems to me that the retard port at the back of the advance can on the distributor should not be connected directly to full manifold vacuum.
Again, I could be wrong, but it would be nice to find that diagram. Just to be sure.

 

[DirtDonk]

Your PCV valve is routed correctly to the base of the carburetor at the spacer.
Your heated choke stove is only half functioning, and could constitute a tiny vacuum leak.
The metal tube wrapped in heat resistant fiber should be attached to the threaded fitting at about the 7 or 8 o’clock position of the choke housing on the carburetor.
The missing second half of that would’ve been another metal tube coming up from the exhaust manifold adjacent to that tube. The second tube runs up to near the carburetor, where a rubber hose continues the journey to that angled fitting that you can see in your pictures with the black rubber cap on it.
The vacuum being pulled through the choke and exhaust manifold are potentially a small leak. Small, but maddeningly enough to create a rough idle.

 

[DirtDonk]

If you can feel vacuum at the PCV valve, then while the engine is running with the oil fill cap removed, place your hand over the hole.
If you feel a slight vacuum, then blow by is not overpowering your PCV and is probably not the root cause of your problem.
If, on the other hand, you can feel pressure building up in spite of the PCV sucking, then you apparently do have some blow by.

During the leak down test, air coming up through the carburetor is a leaking intake valve. Not the valve, stem seal, but the valve itself.
Feeling air coming out of the dipstick tube is worn rings and are typically the major cause of low by.

With the engine idling, even with the PCV intact, don’t worry over much about oil vapors looking like light smoke that might be coming out of the valve cover. That’s pretty normal from the heating process.
A lot of of it is not normal however! A little is.

How often do you drive it? If it sits more than it drives, you might be seeing fatigue of the piston rings.
Could be buildup, or they could just be old.
If it was mine, I’d be driving it fairly often and be adding plenty of oil additives designed to free sticky lifters and rings, and generally de-gunk the inside.
It’s not a cure-all, but it’s a big help for mildly under utilized engines.
Don’t ever do it though, if pulling a valve cover shows you that there’s tons of built-up gunk. That requires a whole different direction.

 

[Oldtimer]

With and without smog pump (thermactor). Copied from 68 shop manual.

 

[Oldtimer]

No help on choke plumbing.
68 was manual choke only.