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BBC - Oil Cooler Location


Well-known member
I have a question for my car motor crew:

currently running a 540 BBC and i added an oil cooler. its added at the middle top of the cage with a sandwich plate between block and oil filter. i over filled the oil to compensate for the extra capacity of the cooler and lines but notice that after long runs and the oil runs through the cooler as it should, going down the banks ans such i see the oil pressure drop as if the pan is empty, mind you i have an extra 2-3 quarts in the pan above the fill line. what do you guys think im doing wrong. normal flat running is fine and even on dry ground, only when i enter back into the water and the nose dips a bit. i would run it at the bottom below the engine but i fear with all the crap that get sucked into the radiator as is its more of a pain.

let me know what you guys have done thats tried and true. ill post close ups of set up when i see the boat again.
I can't fully answer your question about why it's doing what it is doing but I can tell you that running 2-3 quarts over the fill line isn't good. Most oil coolers don't hold more than a half of quart more than what the motor holds. Also even with the oil cooler you should still use the full mark on the dipstick because the oil cooler doesn't change oil level full once it fills the oil cooler. The only thing I can think of is that maybe because you have the oil cooler above the motor that it is creating an air pocket and causing the oil pump to cavitate. I run an oil cooler on my 540BB but it's under the motor in front of the radiator and I also run a 180° thermostat for the oil cooler and I have no problems.
I have cracked 2 oil pick up tubes over my years FYI

Maybe plug off the cooler and see if it it still occurs?

Curious as to WHY you added the cooler to begin with ?

What was your oil temp vs engine temp ?
ill have to post a pic of the setup for you guys to better understand but i see what you guys are saying

i got the mount from marks airboats in franklin and they tend to run their coolers above the engine and i havent heard of any issues doing so.

its a rather big oil cooler (10"x10") approx and the lines are over 5' long each so i added an extra quart to compensate for the added volume.

i also understand that overfilling the oil is bad and causes windage problems but id rather overfill then spin a bearing losing oil pressure. correct me if im wrong here fellas.

i run an oil cooler because we do alot of hard running and i noticed my temps were a little higher than i liked and the engine builder suggested i do so. i dont see it hurting anything, ill say it does help in keeping the temps in check on hot days here in south la and i have less of a dieseling problem after appropriate cool down after hard runs. i always run 93 octane in this AB too.

again its only when going back into the water and the bow of the boat in lower than the back. acting like its low on oil hence why i added some.

i think im going to move the cooler to below the engine and redo the lines and see how that works, drain some oil out and try again.

pics of proven set ups will help me as well if anyone has pics offhand.
Do your oil lines enter at the top or the bottom of the cooler? They should enter and leave out of the top so the cooler stays full of oil, not air. If they run to the bottom of the cooler, I can envision the issue described.

I agree with Gladesman, you should have a cooler bypass thermostat system to improve warm up time.

Gladesman06 said:
I also run a 180° thermostat for the oil cooler and I have no problems.
This is also a very good possibility. If your pickup tube has a crack up high or even a possibility that the pickup tube came out/broke off. This would make since of why it's only doing it when the boat is going down hill. This would mean the oil is running away from the pump, causing it to suck air. This would explain why it's only doing it when the nose of the boat is downhill. If the pick up tube came out of the pump normally you would usually lose pressure pretty much completely but if you are running extra oil like you said the oil could be covering the inlet of the pump enough for normal running but not when going down hill. This is probably a long shot but I've seen crazier things happen lol.


I have cracked 2 oil pick up tubes over my years FYI
So to be clear you did not have these symptoms before adding the oil cooler and adding the extra 2-3 quarts of oil to the system?

Here are a few posts from a racing forum on overfilling the engine with oil.

"If the oil level is too high, it contacts moving parts in such a manner as air is mixed into it. The result is air pockets in oil galleries, and less liquid oil to cool parts such as piston skirts. The "foam" also sticks in place and doesn't drain back to the pan, and insulates parts from normal heat transfer."

"That extra oil ends up splashing around the crank and under the pistons creating windage. Windage can cause aeration in the oil which reduces the oils ability to pull heat from the engine. Even though modern oils have anti-foaming agents that aim to reduce the underlying cause of foaming, the high amount of windage makes the oil more vulnerable to it."

This may not be the issue but sounds eerily similar to what you describe.

Great input from the other guys!!

Hope you find the culprit! :salute:
i ran the boat this weekend and noticed it still would do it. when i got home i flipped the oil cooler to have the lines enter from the top. due for an oil change and will fill to full mark and that is, to be clear, i only added 1/2 - 3/4 a quart over full. i do know BBC have windage problems and are aware of the issues.

we run the boats hard down here and after 3 engines in the same hull, i would rather keep this one cool as possible. i did notice a significant drop in overall engine temps once i added the cooler.

i am hoping the flipping of the cooler eliminates my issue which it sounds like it should as the boat runs great everywhere else now.

will keep posting on the findings.