Oil Temp Limits

[PWMAX]

What would you guys think, max safe oil temp would be. Say, 10-15 minutes, at wide open in a marine application?

Frank

[PackardV8]

The oil guys tell me for sustained runs, not higher than 250 for mineral-based and not higher than 300 for synthetics. However, since you've got the whole lake or ocean for a coolant reservoir, why should it ever get close to that high? A good heat exchanger should be able to keep oil and coolant temps exactly where you want them for max performance and durability. For me, that has been in the 200-220 range.

jack vines

[PWMAX]

Jack, thanks for the replay. Thats what I was told at a Joe Gibbs oil seminar not to long ago. About 300 degrees. Reason I ask, this particular deal, the engines are about 820hp, 540 inch, hyd roller Whipple Supercharged, light boost, single carb deals. Under boost the oil temps hit 260 within a minute or 2 under boost, and creep up. I do the engine work for a performance marine shop, that riggs the boats, so, the oil cooler set up, etc, is their deal, but they have the biggest coolers you can get from what he tells me. Not sure if the oil going thru the the blower is adding a bunch of extra heat.

The owner of the boat is paranoid about the oil temps, as he was told by someone else, they should run at 160 all day. The super charged engines seem to be a bit tougher to keep cooler, but, I think 160 is an unatainable temp, for pro-longed periods of time. Not sure what to so, if the guy has rocks in his head, and won't listen, becaxuse someone else planted a seed in his head that won't grow, what do you do.

The game plan is to add another cooler, and put 14 qt pans + cooler volume, from 10+cooler volume. So, probably like 16 qts, vs 12, and add some jet. The engines were tuned on the dyno, on the safe side, hopefully that should help keep them in check.

Frank

[PackardV8]

The 160 is OK for coolant temps, but oil temps need to run 200-220.

I've put oil temp gauges on many cars and boats. Just cruising around, the oil takes forever to get as warm as the coolant. However, put a sustained load on the bearings and it shoots right on up there and will continue to rise unless a large and efficient cooler is removing the load-generated heat.

IMHO, adding more oil just takes it longer to warm up. Twenty-eight quarts will eventually get too hot if the cooler isn't large enough or plumbed into external water exchanger.

but they have the biggest coolers you can get from what he tells me.

Not likely. They probably mean as large as they usually use. Larger and more efficient than they are using are definitely available.

I don't think the supercharger itself is adding the heat; it's just the bearing loads. High compression NA engines behave the same way. Let us know how you solve the problem.

jack vines

(P.S. - getting so frustrated you start mixing your metaphors will not lead to clear thinking ;>)

Not sure what to so, if the guy has rocks in his head, and won't listen, becaxuse someone else planted a seed in his head that won't grow, what do you do.

[MadBill]

There's certainly no reason to aim for less than say 220°F.
Oil temp as mentioned is due maybe 85% to the power developed. Our road race Trans Am car puts out ~ 820 HP and races for an hour at a 9,000 RPM limit without the oil exceeding 240°. At that, we have one strip of tape across the rad inlet to keep the coolant above 180°. It uses a heat exchanger inside the rad end tank, which can't be nearly as effective as one exposed to lake/sea water. There has to be something wrong with the combo: Not enough water through the exchanger/not big enough, oil flow problem..

[Whitewater Racer]

Oil in a marine motor needs to get to at least the boiling point of water and maintain for a while to get the condensation out. Marine motors with lake / river water cooling seem to have a tendency to "add" condensate water to the oil. They are really bad, it seems, if they are under a cover that is exposed to bilge water in any way. (Not so much when running but after they are shut done they will condense water). You need to get enough oil temperature to get it boiled out. Marine motors will quite often have the milky residue from water on the dip stick, in the breathers and under the valve covers. On a tear down they tend to be rusty inside! Not enough oil heat for a long enough time to get it vaporized and "out".

Quite often the plumbing of the coolant water goes to the exhaust FIRST to warm the water before it goes to the oil cooler so as to afford quicker oil temperature rise. I have even seen them go lake pickup to exhaust cooling to motor cooling to oil cooler. The water temperature entering the cooler is already at 160+°. Then it is not much different than an oil cooler in a radiator. Check the plumbing. Maybe try altering it. (I dedicate one pickup coolant stream to the oil cooler ONLY and then ball valve it to try and keep some heat in the oil. We run in rivers where the water temperature is sometimes only 50° and unless you choke down the water flow you can hardly get any oil temperature).

[xenginebuilder]

Under boost the oil temps hit 260 within a minute or 2 under boost, and creep up.

I would ask where the oil temp is being monitored. If from the pan, that temperature will be pretty high just because it is the hottest place to collect after flowing through the engine, and I would think has no air flow across it to help cool at all. Of more interest would be the temperature of the oil entering the engine AFTER the coolers and filters. That temperature should be pretty easy to control to within 20-30 deg of coolant temp under any load. The "real" oil temp may be better than you think.

[jsgarage]

Some thoughts: a major oil company once instrumented a running V8 engine (likely a SBC; can't remember) on a dyno to check oil temps everywhere inside the block. They found that relative to oil in the pan which they got to 290F, loaded oil temps in the main bearings were up to 40 degrees hotter at 330F! So your 260F oil in the pan might be well above that in some other areas of the engine. A second thing to consider in your boat motor is, oil at maybe over 260F is being sprayed onto (possibly) teflon valve guide seals, which are known to melt at 250F per the mfgr. Super-hot oil isn't doing o-rings & main seals any favors either and the viscosity of most oil at 300F is close to that of beer- and lubricates about as well. FWIW, I like oil running no hotter than 200-220F- measured in the pan like everyone else. Doing this, I haven't had to sweep up a fragged engine since the flathead Ford days.

[PWMAX]

Thanks for the replys guys. Like I said, i don't rig the boats, so, I don't know where they are getting temp readings from, but thats something to look at. I know 200-220 is where the natural engines run, and thhe mercruiser engines are set-up to run 200 degrees. We will see what happens. The funny thing is, these things haven't skipped a beat in 3 summers, but now, someone tells him that they should run 160 degree oil temps, and the guy is giving the boat shop a bit of a hard time about it. So, we shall see what happens. Thanks for the insight

Frank

[Kevin Johnson]

You need to determine if the running oil level is so high that the rotating assembly is constantly churning it. That will really raise the oil temps and have no relationship with rejecting heat from the engine -- it is generating heat. Be sure to take into account the angle which the engines sit at relative to the surface of the water. The rotating assembly should not be striking the oil in the sump when under steady state power output.

[PWMAX]

Keving, thats a good point. These have the stock 10 qt, deep sump pans as used on the HP500 502's. These are nice pans, but maybe the extra stroke could be getting into the oil. Although, we have done numerous 540's out of the 502's, naturaly aspirated, without this issue, with the same pans. Something to look into though, thanks

Frank

[Kevin Johnson]

Keving, thats a good point. These have the stock 10 qt, deep sump pans as used on the HP500 502's. These are nice pans, but maybe the extra stroke could be getting into the oil. Although, we have done numerous 540's out of the 502's, naturaly aspirated, without this issue, with the same pans. Something to look into though, thanks

Frank

A big variable is the angle that the engine sits at while at speed. You will need to determine that and this could vary boat by boat and has no reflection on your builds. Deduct about two quarts for oil circulating through the engine while running. Fill the pan with water and start tilting. You will be looking for the angle at which the water starts flooding the windage tray. Remember that when the air starts getting churned in that the gross volume of the air-oil mix in the sump will increase. A nice estimate would be 20%. Add that extra amount of water and start tilting the pan again. The angle will decrease.

You might want to get a digital level and set it on the boat deck arranged so that it is accurately parallel to the centerline of the crank. Take the boat for a spin and read the angles directly at different speeds/power-levels.

[cfm]

I have played with many marine engines. Edit in: running 'hard' for over 1/2 hr at a time is not uncommon around here. My personal record is near 40 minutes. Granted, that was with a mild motor.

I Always try to get the temp under 250 measured at the pan.

Oil temp is far more important than water temp. Meaning, if you have to lower water temp to lower oil temp, you do it ! This is why most blower motors do not have water t-stats. (They may have oil cooler t-stats though, depending on temp of water boating in).This (running without water t-stats) is something I didn't want to do when first getting into boats and thought the boat guys where crazy for doing so, but now I understand.

Lastly, tune can change oil temps drastically. Have seen a few motors (mostly blower motors) run reasonable oil temps after re-jetting the carbs a little richer.

Of course, having the proper sized oil cooler is number #1 in keeping oil temps at bay.

[Kevin Johnson]

I have played with many marine engines. Edit in: running 'hard' for over 1/2 hr at a time is not uncommon around here. My personal record is near 40 minutes. Granted, that was with a mild motor.

I Always try to get the temp under 250 measured at the pan.

Oil temp is far more important than water temp. Meaning, if you have to lower water temp to lower oil temp, you do it ! This is why most blower motors do not have water t-stats. (They may have oil cooler t-stats though, depending on temp of water boating in).This (running without water t-stats) is something I didn't want to do when first getting into boats and thought the boat guys where crazy for doing so, but now I understand.

Lastly, tune can change oil temps drastically. Have seen a few motors (mostly blower motors) run reasonable oil temps after re-jetting the carbs a little richer.

Of course, having the proper sized oil cooler is number #1 in keeping oil temps at bay.

Adding a windage tray assembly to a NA 2.4 Dodge lowered oil temps from 231 F to 207 F on the dyno AND lowered coolant temp 10 F (7500 rpm). The thermostat was set at 195 F and the factory oil cooler was being used. This was with the proper amount of oil present. Adding a little too much oil to an SR20 will kick the oil temps over 300 F. In drag runs without a windage tray, the turbocharged version of the 2.4 engine can lose as much as 40 hp to windage friction -- sustained over time that would be a huge amount of heat.

Do you suspect that they were messing with the tune? It sounded like you had initially adjusted it on the dyno as with your other engines to keep the oil temp down.

[robert1]

The dirt late model motors I build all run around 260°, some more. 260° wouldn't even concern me.