The cold temps and oil pressure....

So it has dropped to below freezing a few times recently and I needed to use the 8n this weekend ( side distro, 12v, 33 hrs on full rebuild).

I started it up and my oil pressure was terrible. I usually get 50psi at idle during startup and then it ocmes down to 20-40 idle to max rpm when warm.

Yesterday it was down to 5 psi to 20 at idle to full rev.

I would think colder temps would make it more viscous = higher pressure?

Theories:

1) Gauge did not like cold weather and was not working.

2) Crank shrunk a few thou and spun bearing

3)????

Any ideas? If I didnt have 33 good hours on the rebuild, I would say I f'd the bearings again and I lost oil pressure. But on startup after it was cold?


Thanks for any ideas,

Cam

(quoted from post at 08:07:35 11/03/14) So it has dropped to below freezing a few times recently and I needed to use the 8n this weekend ( side distro, 12v, 33 hrs on full rebuild).

I started it up and my oil pressure was terrible. I usually get 50psi at idle during startup and then it ocmes down to 20-40 idle to max rpm when warm.

Yesterday it was down to 5 psi to 20 at idle to full rev.

I would think colder temps would make it more viscous = higher pressure?

Theories:

1) Gauge did not like cold weather and was not working.

2) Crank shrunk a few thou and spun bearing

3)????

Any ideas? If I didnt have 33 good hours on the rebuild, I would say I f'd the bearings again and I lost oil pressure. But on startup after it was cold?


Thanks for any ideas,

Cam

Click to expand...

Colder temperatures do make oil more viscous = higher pressure. But more viscous also means it is harder to pump which can result in reduced/no flow and low/no pressure at cold startup. That is why the viscosity of the oil needs to match the ambient operating temperature.

In 1940 Ford specified viscosity grade SAE 30 for use at ambient temperatures consistently [b:2584e6eedc][u:2584e6eedc]ABOVE[/u:2584e6eedc][/b:2584e6eedc] 90F, SAE 20 for temperatures between 32F and 90F, and SAE 10 for use at temperatures [b:2584e6eedc][u:2584e6eedc]BELOW[/u:2584e6eedc][/b:2584e6eedc] 32F. That of course was a tradeoff between cold startup and hot operating temeprature viscosity. Today we have high quality multi-grade oils and a modern SAE 10W30 covers that entire range with no viscosity tradeoff and no need to change grades with the seasons.

So what is in your sump?

TOH

20w50.

I'll try 10(15)w40 tonite.

Basically, even though the pressure would be higher with more viscous, the pump would need to be more robust to overcome to internal shear/friction due to higher viscosity?

(quoted from post at 08:46:22 11/03/14) 20w50.

I'll try 10(15)w40 tonite.

Basically, even though the pressure would be higher with more viscous, the pump would need to be more robust to overcome to internal shear/friction due to higher viscosity?

Click to expand...

No - the difference is the same as drinking a thick milkshake versus ordinary milk through a straw. With the milkshake you have to suck harder and you still get less in your mouth.

When the oil is extremely viscous it is much harder to draw the oil out of the sump and you get a reduced flow into and consequently out of the pump. Reduced flow to the bearings = lower pressure at the gauge.

TOH

At the risk of continuing to beat a dead horse....

You really don't need or even want a grade 40 oil in an N-series. You have a rebuilt engine with good oil clearances and a grade 30 is MORE than sufficient in terms of producing a strong/thick oil film. Anything heavier is quite literally a drag on the engine AND it inhibits cold cranking and pumping.

Don't be fooled by the 15W in a 15W40 grade label. Here are typical viscosity curves for grades SAE 10W30, 15W40, and 20W50. All your engine needs is a viscosity somewhere around the values on the far right side of the graph and ALL of those oils are very close together and ALL of them are fine when hot. But there is a huge difference in their cold startup viscosity and the LOWER you can go on that end the better for your newly rebuilt engine.

Using a heavier than needed oil does not get you more protection when hot and in cold startup conditions actually gets you less.

TOH

(quoted from post at 09:55:21 11/03/14)

(quoted from post at 08:46:22 11/03/14) 20w50.

I'll try 10(15)w40 tonite.

Basically, even though the pressure would be higher with more viscous, the pump would need to be more robust to overcome to internal shear/friction due to higher viscosity?

Click to expand...

No - the difference is the same as drinking a thick milkshake versus ordinary milk through a straw. With the milkshake you have to suck harder and you still get less in your mouth.

When the oil is extremely viscous it is much harder to draw the oil out of the sump and you get a reduced flow into and consequently out of the pump. Reduced flow to the bearings = lower pressure at the gauge.

TOH

Click to expand...

Now I want a milk shake! Darn...and I am trying to lose weight.
But none-the-less excellent analogy

Would you believe this?

Before they came out with multi-ciscosity oils, we would replace the 40 wt. oil with 10 wt. oil.
Part if the winter prep for our snow plow..9N.

Or, simply drain the 40wt. oil, wait till the plow is required, and heat-up the oil on the wood stove. Pour the warm oil into the engine and plow away!

Lots of times, we could not get the 10wt. oils.

John,PA

I would not be concerned at this point about viscosity numbers until you get some pressure numbers with a known good pressure gauge. Don't trust your oil pressure gauge yet. Post back with cold idle and 2,000 RPM psi readings from a known good gauge AND operating temperature idle and 2,000 RPM tests. What viscosity oil is in the engine now?

TOH,

Good news is today (50-60 ish degrees in Ohio) everything was back to normal on the gauge.

You made a believer out of me yet again haha.

Definitely an interesting topic for BITOG website.

What pressure does your 8n generate, warm, with 10w30?

Ideally, if mine is drastically lower/higher. I know how to dial in what will work with my tractor over winter.

Thanks,

Cam

(quoted from post at 21:40:28 11/05/14) TOH,

Good news is today (50-60 ish degrees in Ohio) everything was back to normal on the gauge.

You made a believer out of me yet again haha.

Definitely an interesting topic for BITOG website.

What pressure does your 8n generate, warm, with 10w30?

Ideally, if mine is drastically lower/higher. I know how to dial in what will work with my tractor over winter.

Thanks,

Cam

Click to expand...

I use a conventional 10W30 year round. Our winter lows are seldom below 5F. I have a pretty good history on my 8N and it's had a pretty easy life. AFAIK the engine has never been apart and at cold startup pegs the 50 PSI gauge. When fully warmed up it idles just below the 30 PSI mark and at 1500 RPM it is a just above the 40 PSI mark. I have never checked the calibration on the gauge.

TOH

PS> Shortly after we moved in here we had a bitter cold snap - ovenight lows below 0F. I decided to start my prized Thunderbird Turbo Coupe and let it warm up a bit before I went to work. Came out 5 minutes later and the car was not running and would not start. Turned out to be a wiped cam caused by overly thick oil that left the upper end high and dry. Despite what all the Roger Ramjets had said Castrol GTX SAE 20W50 was not a "better idea" in my Turbo Coupe.