I'm a little puzzled by this... Normally I expect the engine to be loose when cold and tighten up when it gets warm. But my engine has almost no detectable blowby when cold, and it's a solid stream coming out of the vent when hot.

I'm expecting to do the shortblock this summer, but was wondering what people thought this might be.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

Since you haven't had anything helpful yet, I'll take a stab in the dark. Worn valve guides/stem seals? Have you done a compression test?

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'66 Dodge Dart

Head was rebuilt about 5000 miles ago. I have no reason to think this is an issue.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

A bit of blowby is normal. That is why road draft tubes and then PCV valves were invented. Have you done a compression check?

Not after the valve job.

I'm going to build myself a new shortblock this summer to put under my head. I'm just puzzled by what it does, and how much it is. I would normally expect an engine with this much blowby to use a lot of oil, and it doesn't. It does seem to use a little (it leaks a little, too, so hard ot tell which is which), but certainly not a lot.

I want a forged piston engine, balanced, proper bore and hone job, moly rings, and so on. Not the half baked job that most machine shops do.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

Several years ago I had the 351W motor in my Ford van rebuilt. It would dump oil in the air cleaner through the breather and had a very strong and steady stream of blowby once it got warmed up. It turns out that the topmost piston ring (I believe it was an oil scraper) was GONE on all the pistons. Not worn out, but GONE, as in physically not present. The rebuild cured the problem.

I'm betting you have worn cylinders or rings.

On the other end of the spectrum, one of my sisters has an 03 Buick Rendezvous with the GM 3.4 litre v-6. The motor has 116,000 miles on it and doesn't smoke or leak a drop of oil, but it burns through a quart of oil about every 1000-1500 miles. Plenty of power and decent fuel economy given the vehicle, but the oil consumption is concerning. I am probably going to end up pulling the engine and getting it rebuilt sometime this year or next.

Solid stream of blowby out the crankcase breather is no good. You're right to be puzzled by why hot and not cold; the other way round is more common. Whatever's causing the excessive blowby is expanding/opening up as it heats. Sounds more like a hole in something than a crack in something; cracks often close up with heat.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

This is fairly common on modern engines, esp if eng oil isn't changed every 3000-4000 miles. The cylinder bores & compression rings will be in great shape- comp test will be good, leakdown test will be under 10%. However, the (low tension) oil control rings will have seized due to carbon build up & the engine will consume lots of oil.

As far as more blow-by when hot, I'd hazard a guess that the blow-by gasses are just more visible when things get up to temp. On a cold engine all the moisture & lighter contaminants in the oil can't "boil" out into the crankcase- until you add some heat.
( I could- I say I COULD, be wrong....do-DAHH! )

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63 Valiant Wagon
225 - 4 bbl

Cannot agree. The necessity for a 3k-4k mile oil change interval is a shamefully wasteful myth in the vast majority of cases.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.