OT break in oil for a new car

[clare]

No, the filters don't bypass when cold or reved. The oil pressure regulator does. Two totally fdifferent animals.

[Zootal]

Yah - the filters only bypass when the filter element is sufficiently plugged. Oil pumps have a pressure regulator that bleeds oil back into the crankcase if the max pressure is exceeded. This happens at cold startup and high rpm.

[Zootal]

FWIW - one of my old instructors built race car engines, and he told us of the time he put a high volume oil pump into one of his engines. Took it out on the track and the engine siezed before he completed one lap. Come to find out that the drain holes in the head were not big enough to drain the oil into the pan as fast as it was getting pumped to the rocker arms. The top of the engine filled up with the oil, oil pan went empty, and bye bye engine.

[Jules]

and it's fun when they break on old vehicles and the engine's sitting there recirculating unfiltered oil - then the particles jam up whatever the smallest oilway is and things go bad from there...

[Tony]

I thought at least some filters have a bypass in them? Maybe not but yes on the pressure regulator, wasn't thinking, just typing.

[Jules]

Maybe. The last old car I had used a cartridge filter (i.e. the cartridge was replacable, but the housing was retained - unlike modern filters where the whole filter can is swapped). The cartridge was held in place under spring tension by what was essentially a valve - too much pressure (or a blocked filter) and the valve would open.

Whether any modern "all in one" filters have a built-in mechanism like that though, I don't know.

cheers

Jules

[clare]

MOST filters have a bypass on them, but they are set to bypass when the pressure difference across the filter gets too high (blocked filter) GENERALLY they do not come into play from cold, and virtually never because of high engine speed (which increases oil flow - and therefore pressure across the engine clearances, but not the filter.)

[The Daring Dufas]

Do you remember the toilet paper oil filter cartridge kits? It was a reusable filter replacement for the spin on throw away filters. I saw ads for them but never got my hands on one of them. Some toilet tissues I've come across remind me of oil filter media material. OUCH!

TDD

[Tony]

All oil filters restrict oil flow. Some more and some less. If they didn't, they couldn't filter. Cold oil is less fluid and causes the pressure difference to increase. Revving the engine pumps oil faster. Wherever there is a restriction the greater the pressure difference.

One very cold day I saw a guy at work start his car. He always revved it up when it started, and he only used 30 weight oil. That cold day the oil filter blew out from all the pressure and he had quite a mess to clean up and a filter to replace. I suppose the bypass or regulator in the motor was a little too little, or a little to slow opening up.

[dpb]

Tony wrote: ...

Which is why any modern vehicle will specify multi-grade oil. There the viscosity is modified by the additives to _not_ increase drastically w/ temperature...

The failure you state was an extreme aberration at best; I'd think it more than likely it was a case of either wrong oil or cheap filter or combination of both and perhaps other causes as well...

--

[Zootal]

I seriously doubt that revving the engine on a cold startup with 30w oil would blow the fitler. The oil pump pressure valve would limit the pressure to 60-80psi or so, no matter how cold or thick the oil is. The filter can take a lot more pressure than that. I can think of several things that will blow a filter - faulty installation or the wrong filter can blow out the gasket. A defective filter could blow, but that is pretty unlikely. My next vote would be that the oil pump pressure valve stuck shut. I've seen that happen - it is extremely rare, but on a cold tight engine with heavy oil and a sticky valve (it's just a ball and a spring, after all), the oil pump can put out a couple hundred psi or (much) more if the check valve sticks shut.

*That* will blow out the oil filter! Real fast, and quite spectactularly! And it will make a mess as oil under high pressure sprays all over the place. And if you don't catch it in time and just keep running the engine, in a few moments the engine itself will quite nicely sieze.

[Tony]

I completely agree. I should have worded it better to say that the bypass wasn't good enough *for the wrong type of oil he used*.

[Tony]

I don't see what you are trying to say. If you have seen a filter blow, don't you think it would be more likely to happen if the vehicle also had the wrong oil, temps were extremely cold, and revving the engine? I think those three things would surely raise the chance of blowing the filter.

[Zootal]

Those three things would only raise the chance of blowing the filter if something else was wrong in the first place. If nothing else is wrong, those three things would not mean anything. You can't blow a filter unless the pressure is too high, and the oil pump keeps the pressure from being too high, even if the oil is cold and thick and the engine is revved.

[Phisherman]

I've always changed mine after the first 1000 miles and then every

3000 miles. I've stuck with Castrol.

[clare]

Again, nothing to do with the filter bypass. Although in extreme cold with thick oil, the bypass COULD come into play, it would have NO EFFECT on the problem you noted - blowing the filter off.

[clare]

You might think so, but a 20Wx oil at -40 in a slant six dodge can pruduce oil pressures up around the 200psi range on initial startup. This is because at that temperature the pressure releif (or regulator) valve can be extremely reluctant to move. Don't need to rev the engine either

I've blown a filter off a slant 6 myself (20W50 in Winnipeg, of all the stupid things) and have also seen it happen numerous times with straight 20W20 oil at -20F - on other brands. On mine it blew off at IDLE. Also had the oil pump drive on a Ford 351 twist off in a similar situation.

[clare]

In your dreams.

[Tony]

Exactly! Having the wrong oil means there IS something wrong with the engine. It has the wrong oil! And it makes the bypass move a little, or a lot slower and presto, blown oil filter.

Ever try to pull start a little briggs engine with straight 30 weight oil in the middle of winter. You better believe things move slow.

[Zootal]

If the pressure regulator is reluctant to move, then that is what is wrong with the engine...