V-twin oil pump pressure - ok for a larger cooler?

[VeeTwin]

I'd like to put a larger oil cooler on my Duromax 713cc engine (Honda clone). Like something for a car or truck transmission. I'm pretty sure the oil pump would have a pressure bypass and I'm concerned that by increasing the size of the cooler, it might cause too much back pressure causing less flow through the filter/cooler route causing worse cooling than better.

Is my understanding of the oiling system correct and do you think this is something to be concerned with?

[slonomo]

I wouldn't use a larger cooler for the reasons you described. Not that it won't work, but the risk is engine damage. I wouldn't want to be the guinea pig, ya know?

Does that engine come with a cooler? If so, why not keep it small and rig a small fan to it? Or fabricate some kind of cold air scoop that feeds cooler outside air, rather than underhood warm air. That's the route I would go. You could even make a "cool can" type thing for the oil if you really wanted to cool it down. I have also seen some pretty nice intake fans for the engine compartment on some carts. They are a little noisy, but if temps are getting that hot that you are concerned, sounds like more cool air would be the ticket?

[VeeTwin]

Yes it comes with a little plate cooler that's attached to the side. There are louvers on the engine air ducting that are meant to redirect air from the flywheel fan over it. But I am dubious of how much air flows over it and it would already be hot from flowing over the cylinder fins.

Mounting it in cool air with with a fan is another idea I can look into. The charger on this engine is weak though so it will have to be a weak fan maybe even with a resistor to reduce the current draw.

What is a cool can? Is that just like a little external tank that holds extra oil?

[VeeTwin]

I did a search on pressure drop from oil cooler and found this post in an automotive forum which describes the opposite of what I was thinking but makes sense:

"Actually, a larger cooler should provide less resistance. Basically, you have a fixed flow rate of oil that has to pass through the cooler. The more rows you have in the cooler, the more parallel paths there are for the oil to take. The more paths there are the slower the oil moves through them, and the less total resistance there is.

Imagine it like this: Each "row" is maybe the size of a -3 line. Probably smaller. So if you had a "1 row" cooler, then your -10 supply line has to drop down to a -3 to get through the cooler. But if you have 10 rows, then you are running your -10 supply through 10x -3 lines."

So a larger tube-and-fin cooler would increase pressure drop, but a larger stacked plate may actually reduce it.

[Dave in VA]

My 23hp Vanguard had the oil cooler mounted to the intake shroud, very close to the flywheel. Holes in the shroud allowed cooling air to be blown thru the cooler.

I rotated the breather straight up to prevent oil from being blown out...

[slonomo]

What kind of oil temps are you seeing now? And what is the temp on the cooler intake side vs discharge side? Take note of the temperature in the engine and then how much temp drop you get as your baseline. Do you need more cooling capacity based on those numbers?

Adding a larger oil cooler means adding more distance that oil has to travel from intake to discharge of the cooler. Will the stock oil pump withstand that? No way to tell. A car engine's oil pump has the capacity to do that, but does a Briggs Vtwin?

I'd focus on where you are now and see if that cooler even needs upgraded.

For Air Cooled 4 Stroke Engines:

Oil sump temps on an air cooled engine should be in the 230 degree F range. Higher than 250 in the sump is cooking, time to let it cool down. Ambient air temps have a great affect on overal oil temps.

Oil temps on the valvetrain will be higher, maybe 250-270, so expect to see a 30 degree rise in temps at the top of an engine. More of a rise if you run higher compression and run higher revs.

Conventional oil starts to degrade at 275 degrees. Synthetics can tolerate a few more degrees. Frequent oil changes are key no matter what oil you run, due to high temps on air cooled engines.

Expect a 10 degree temp drop on a well ventillated oil cooler. If air speeds are low, and air is hot, expect this to be lower. If air speeds are high and air temps are low, expect more than 10 degrees drop. This is why a fresh air vent duct and electric fan are helpful. The air coming off the engine fan is usually 200 plus degrees, more on a hot day and at low speeds. Outside air, even on a hot day will be half of that. It's all about heat transfer.

[VeeTwin]

I have a temp gauge in line with the cooler. I mounted it several months ago and **** if I can't remember if I mounted it at the inlet or the outlet of the cooler! So far the highest I've seen the temp is around 180, but I don't know how exactly that would relate to the crank oil temp.

That doesn't seem too bad, but this is with only short spurts of hard riding, maybe 10 -15 minutes, in 70-80 degree weather. I want to make sure it's safe under more continuous operation.

This engine is modded and I do notice higher temps vs when it was totally stock. I've had the heads planed and ported by perfm670 and I used a thin head gasket, tougher valve springs, dual carbs on a custom long ram intake and dual exhaust. I run 93 pump fuel and Amsoil Z-ROD 10w30. I have a tach and try not to rev it past 5500 for safety sake.

[slonomo]

180 is pretty good. If that's after the cooler then your sump temps are likely 200-210 range. Yes hot ambient air makes a difference, as does humidity, and the speed of the engine. 5500 is cooking. You might egg out your con rods doing that kind of rpm. I guess that'd be a good reason to get some billet rods with bearings then.

[VeeTwin]

eww, I sure hope that doesn't happen to the connecting rods The prospect of having to remove and tear down the motor would be a bummer, but more importantly, I don't know where I'd get billet rods for this motor. I only wing it up to 5500 for very short bursts. Mostly I'm operating it in the 3000 - 4500 RPM range during typical fun-runs