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Oil coolers and pressure drop calculations

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sdiesel
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Oil coolers and pressure drop calculations

Post #1 by sdiesel » Tue May 19, 2020 11:51 am

For the engineers among us here, please address a question that has arisen in my experimentstions.: Pressure drop.

The v8 Ford and likely the six can benefit from oil coolers assuming there is a heat problem to begin with.
In my case heavy trucks, lean burn early EFI, pollution - tuned engines that don't have the benefit of modern tech. Thus tend to run very hot.

In my current dalliance with an older 250 pickup the 351 small block has a reputation for self destructive behavior without attention to the temps.
So... I have removed front license plate ( read, lost the front license plate), and in it's stead have carefully cut a 3x11" rectangle in the bumper, behind this opening, is a fluidyne radiant cooler.
1/2" npt, and -10an fittings.

Pressure drop.
How do I address this, is it a concern?
If I add remote filters downstream from the cooler will it create a " backpressure" to hold pressure drop to a minimum?
If the cooler is full, and filters are full, is there even a pressure drop to contend with?

Engine currently enjoys a very solid oil pressure according to the factory gauge,, very healthy.
Compression is so-so and I attribute that to dirty rings which I'm addressing in a different manner.
I expect that to improve.

So, healthy engine, and oil cooler what do I do about pressure drop?

Further, it seems a temp gauge is in order and possibly a thermostat for the oil.

How have others addressed this issue outside of strict racing vehicle applications?
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

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bubba22349
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Re: Oil coolers and pressure drop calculations

Post #2 by bubba22349 » Tue May 19, 2020 1:29 pm

Other than a little increase in the engines oil capacity I don't see any reason for a pressure drop during normal operation. Might be a little lag to build pressure during engine start up if there is compleate oil drain back of the oil cooler (depending on its install height) after the engine shut down and when sitting maybe a one way check valve installed in the oil return line could help with that. Good luck :nod: :thumbup:
A bad day Drag Racing is still better than a good day at work!

I am still hunting for a project car to build but with my current low budget it's not looking so good. My Ex- Fleet of Sixes these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

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Re: Oil coolers and pressure drop calculations

Post #3 by RufusTDoofus » Tue May 19, 2020 2:17 pm

I added an external oil cooler on one of my old Toyota diesels. These engines are old school high pressure/low volume systems with mechanical lifters.

I used a thermostatically controlled sandwich type adapter from Derale. It would start directing flow to the external cooler around 180 degrees F oil temps. I had a mechanical oil pressure gauge on the engine too. When the 180 degree valve would open I'd see a drop of 5 to 7 PSI. 2200 RPM at normal operating temps would drop from 40psi to 33-35psi when the oil was flowing through the cooler. The oil pressure gauge was plumbed into the oil gallery that fed the turbo.

The oil cooler was plumbed with 3/8" ID hose [edited to correct 3/4" ID to 3/8" ID], about 10 ft total including supply/return from where the oil cooler was mounted in front of the radiator. I think all that extra volume was the reason for the drop in pressure.

I'd recommend plumbing in a mechanical oil pressure gauge for a sanity check if you're thinking about going this route.
Last edited by RufusTDoofus on Wed May 20, 2020 6:52 am, edited 1 time in total.

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Re: Oil coolers and pressure drop calculations

Post #4 by wallen7 » Tue May 19, 2020 3:45 pm

I used to remove the plug for the spring at the relief valve and add a flat washer . it will add about 5 psi to the oil pressure. Remember to put a new plug in the pump or weld the hole you drill to pull the plug. I did this when we were racing 240's . Smokey Yunick's theory was 10 psi for every 1000 rpm. Also you might want to upgrade the dist gear retaing pin.

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Re: Oil coolers and pressure drop calculations

Post #5 by gus91326 » Tue May 19, 2020 5:52 pm

I had a similar question when I added my oil cooler to my 200. I ended up not noticing a pressure drop compared to no cooler, at least as far as what my gauge was telling me. Cool away!

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68Flareside240
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Re: Oil coolers and pressure drop calculations

Post #6 by 68Flareside240 » Tue May 19, 2020 6:20 pm

I'm sure I will be corrected as this may not be correct (my collegiate physics courses have been a few years back) but my understanding was that the oil pressure was due to the volume of oil moved by the pump. So for a given volume of oil, in constricted spaces like engine oil passages, gives the oil pressure inside of the engine. This same volume of oil moving, in a larger line (like an oil cooler line) will lead to a lower pressure in that larger line only due to less resistance. So in this closed system, pressures in the engine will remain the same, the only thing that is changing is essentially the volume of oil in the entire system. I'll hang up and wait for the professionals.... :hmmm:

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Re: Oil coolers and pressure drop calculations

Post #7 by pmuller9 » Tue May 19, 2020 7:59 pm

The pressure difference between the oil pump and the oil gallery in the block is proportional to the (resistance to flow) squared x (oil flow rate) squared.

Before the oil cooler and lines are installed the resistance to flow is mainly the oil filter.

After the cooling system installation the pressure difference between the pump and engine block increases by the square of the added resistance to flow.

However because the block sees a drop in pressure the flow rate will decrease and the resulting pressure drop is not as much as if the flow rate was constant once pressure and flow reach an equilibrium.

This brings up the second part of the equation being flow rate through the oil cooler system.
If the oil pump is feeding a naturally aspirated engine with tight bearing clearance the flow rate will be low and the pressure drop will be low.
If the pump is feeding generous bearing clearances and a turbocharger the oil flow rate will be more with an increased pressure drop.

This is one of the reasons why a competition engine uses a multi stage pump and an external oil tank.
The scavenger sections of the pump run the oil through the filter and oil cooler then to the tank and the main pressure section of the pump provides oil from the tank to the engine with nothing in between minimizing the pressure drop.

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Re: Oil coolers and pressure drop calculations

Post #8 by sdiesel » Sat May 23, 2020 9:16 am

Very interesting. A summation will possibly sound like this.
If pressure lines to external coolers are kept not too large , the cooler not too grand, and distances from pump probably are less important than head pressure or elevation of cooler....?
Then I should see no issue with a cobbled together system of remote filter and cooler..
The factory, both Mitsubishi and Ford, see no reason to get sophisticated about this addition, neither even used a t stat on their coolers. Just open lines, a cooler. I get a sense that such a contraption is an afterthought, a band - aid to fix a problem that arose after the fact. Newer Ford's have rather clever and nice coolers for oil, these designs show engineering and careful thot in their design
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

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Re: Oil coolers and pressure drop calculations

Post #9 by pmuller9 » Sun May 24, 2020 12:24 am

sdiesel wrote:If pressure lines to external coolers are kept not too large , the cooler not too grand, and distances from pump probably are less important than head pressure or elevation of cooler....?

No!
The object is to minimize resistance to flow.
Big lines and Big low resistance oil coolers.
Elevation does not matter.
You put the oil pressure gauge in the oil gallery in the block as usual to see what the final oil pressure is and if you need more pressure you will need to raise the pressure at the pump as previously suggested in post #4.

sdiesel
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Re: Oil coolers and pressure drop calculations

Post #10 by sdiesel » Sun May 24, 2020 1:02 am

yes i get that. though not in an equation form. its counterintuitive to open ports to largest size from a smaller size and expect pressure to remain constant. though post 4 does say to increase pressure at pump if this happens. i get that. and head pressure is an issue in almost every pump i have seen it would not apply heare?
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

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Re: Oil coolers and pressure drop calculations

Post #11 by pmuller9 » Sun May 24, 2020 1:35 am

sdiesel wrote: head pressure is an issue in almost every pump i have seen it would not apply heare?

The vertical distance from the pump to the destination being the oil gallery in the block does not change.
Once the oil lines, filters and cooler is full of oil the head pressure is the vertical distance from the source to the destination and the in between can go all over the place with no effect.

If this was not true siphoning would not work.

sdiesel wrote:yes i get that. though not in an equation form. its counterintuitive to open ports to largest size from a smaller size and expect pressure to remain constant.

You cannot compare a compressible gas such as air having the same behavior to a non compressible liquid.
Totally different.

Summary:
Big lines, Big Filters and Big Oil Coolers placed anywhere you need them to be.

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Re: Oil coolers and pressure drop calculations

Post #12 by BigBlue94 » Sun May 24, 2020 12:54 pm

So lemme see if I'm following this correctly...

I added a dual remote oil filter kit and a small oil cooler to my 300, in an 85 bronco. The cooler is a simple tube and fin design, with like 6 bends. The dual fl1a filters are on the frame, just behind the transfer case. 1/2" i.d. hose.

This is most likely to not really affect my oil pressure, if I read this right.

I also think the type of cooler should be considered. Mine, the oil just flows through a single 1/2" tube with fins wrapped around it. Other than the bends, that wont change the pressure, other than from the temp decrease. However, stacked plate coolers are not a single tube. They are like forcing the oil through a bunch of tiny tubes. How do you think, if it would, this could affect oil pressure?

Been too long since I took fluid physics...
1985 Bronco. 309ci I6, NP435, 4.56 gears, Detroit locker and tru-trac, 4" lift, and 37" swamper tires. The 309 is 9.75:1 CR with a Schneider 140H cam, 4bbl, roller rockers, larger valves, and headers.

sdiesel
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Re: Oil coolers and pressure drop calculations

Post #13 by sdiesel » Mon May 25, 2020 1:32 am

And please comment on fittings.
Can 90 degree fitting be used it they are same i.d. as hose?
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

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Re: Oil coolers and pressure drop calculations

Post #14 by THE FRENCHTOWN FLYER » Mon May 25, 2020 9:27 am

Fittings with a smooth generous radius have less pressure drop than sharp right angle fittings. Check out Earles or similar brands.
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Re: Oil coolers and pressure drop calculations

Post #15 by CNC-Dude » Mon May 25, 2020 11:04 am

Every 90° bend in your oil lines or fittings adds 10° more oil temp. So don't go crazy with fittings and use 135° fittings where ever you need to use a fitting.
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sdiesel
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Re: Oil coolers and pressure drop calculations

Post #16 by sdiesel » Mon May 25, 2020 11:29 pm

The increase in temp is due to friction?
Interesting.
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

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Re: Oil coolers and pressure drop calculations

Post #17 by Lazy JW » Thu May 28, 2020 8:01 am

CNC-Dude wrote:Every 90° bend in your oil lines or fittings adds 10° more oil temp. So don't go crazy with fittings and use 135° fittings where ever you need to use a fitting.


During one of my many equipment upgrades in the sawmill business, a hydraulics engineer told me that 9 elbows equals a plug. We used large diameter piping with big, sweeping radius bends. One of the log carriage drive hydraulic power units I worked with had a 400 horsepower electric motor powering the pump; the heat exchanger was massive.
"The White OX" 1974 F-350 300-6, Stock single exhaust, Carter YF, T-18A, Dana70 w/4.11, Flatbed dually w/dump bed. "Where no oxen are, the crib is clean, but much increase is by the strength of the ox" (Proverbs 14:4)
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Re: Oil coolers and pressure drop calculations

Post #18 by BigBlue94 » Thu May 28, 2020 5:13 pm

Lazy JW wrote:
CNC-Dude wrote:Every 90° bend in your oil lines or fittings adds 10° more oil temp. So don't go crazy with fittings and use 135° fittings where ever you need to use a fitting.


During one of my many equipment upgrades in the sawmill business, a hydraulics engineer told me that 9 elbows equals a plug. We used large diameter piping with big, sweeping radius bends. One of the log carriage drive hydraulic power units I worked with had a 400 horsepower electric motor powering the pump; the heat exchanger was massive.


Similarly, I've read every 90° of bend in the exhaust piping, adds the equivalent of 4 feet of length to that pipe. Cant say if it's true, but makes sense.
1985 Bronco. 309ci I6, NP435, 4.56 gears, Detroit locker and tru-trac, 4" lift, and 37" swamper tires. The 309 is 9.75:1 CR with a Schneider 140H cam, 4bbl, roller rockers, larger valves, and headers.

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Re: Oil coolers and pressure drop calculations

Post #19 by sdiesel » Fri May 29, 2020 1:25 am

I was at kinnear specialties today, a hyd. Fab shop. A small place with wonderful owners.
I am weird about fittings and the like could spend hours in their warehouse.and they build some very specific stuff .
I asked abouts 90's. He had an entire row of oiled nineties in boxes. His advice" avoid them when possible,".
Having said that he went on to say " we have need of them often for space constraints so we play with sizes"
Much of what they do is mill related
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

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