High oil temps in jet boats..What's up??

I am a small town engine builder and new to the performance jet boat arena. I have a couple of friends/customers that have come to me over the winter and asked me to build them new engines for their jet boats. After discussing what they thought they wanted/needed in their new motors,(which will both be 496ci's) they both expressed concern that the motors they have seen run in performance type jet boats have all seemed to have very high oil temps and wanted to know what we could do to help this problem. While I know what to do to lower oil temps in most types of engine applications I would like to know what kind of oil temps you guys are seeing in your boats and whether or not any of you are running oil coolers and large capacity pans to help the problem, and what kind of results are you getting. Sorry to jump into y'all's "Jet Boat" forum with a question like this, hell I don't even own a boat right now, I am just trying to do a little research for some good customers of mine who are trying to get me into the hotrod boat motor business. Thanks in advance for any help!

In my application, if anything, the oil temps are low. I'm lucky to get it up to 180. Most jets run cool, due the high pressure and volume of water being pushed through them at speed.
I have seen a couple of guys running oil coolers though.

It's not uncommen for a marine Engine due to the extream load on the Engine to see oil temps almost 100 degrees higher than the water temp. Now this is during extended periods of wide open throttle or close to WOT.
Several combat the high temps with a oil cooler of some sort but some (jetters) don't run a thermostat at all in their engines thus they run kinda cold. However...even with a cold running Jet lets say at 130 water temp...at extended rpm's the oil temp will rise.
The large oil Pans will only slow the temps from riseing...but not stop it. And will also take longer to bring the temps up to a warmer temp for proper operation.
Personally I run a thermostat By-Pass System, temps right at 160-170, a 10 qt Oil Pan and run straight 40 wt. Kendall. The thicker oil doesn't break down as easly as the multi. I've gotten some lifter noise after a long heated run that I don't get with the straight wt. Also some use synthetic oil...not me.
I'm one that won't go wide open for very long as I don't run a oil cooler...if I did it would be a plus. 3000-3500 RPM cruise is good enough for me. (With the occasional HammerDown):cool:

Oil cooler and 10 Quart or more pan are mandatory if the owners/drivers think they have to run WFO for minutes at a time.
Jets put quite a load on an engine at peak output. I would keep full throotle runs to 30 seconds or less. My oil temp will go up about 50 degrees and will lose about 10 pounds at idle for about 2 minutes after a hard pass. That is with a 7q pan and no cooler.
But, if the driver is sane and cruises in the 3800rpm range or less there should not be a big problem with oil heating. Dont let the cool temps on the water temp gauge fool you. The water temp is not going up because it has an endless supply of cool water curculating into the system from the lake. The oil heats extremely fast due to the load on the bearings etc, And cannot exchange the heat at a faster rate than it is being produced, because the oil reserve is mostly setting in the pan and is not in contact with the (relatively)cooler block. But, after the rpm drops after a hard pass, the oil passes through the engine slower and under less load, and it cools back to normal.
Since you are doing the machine work, it is very important you understand clearancing inside a marine engine. The same thing happens(heating cycle) in the combustion prosess. You must run extra clearance for the piston-to-wall and valve guides. The cold incoming water limits the expansion rate of the bores and heads, but the severe duty demanded of the engine causes high combustion temp spikes and causes the pistons and exhaust valves to expand at a very quick rate while the surrounding lake cooled metal has almost no expansion. Seize, ouch, $$$$$$
I,ve repaired several marine engines in our area built by the local self proclaimed hot rod gurus that didnt last 100 yards outside of the no wake zone.

yeah, what hammerdown said. If the motor is going in a heavier boat that will run 4k+ rpms for extended periods (or spinning a small impeller which creates higher rpms for cruising) then oil temps will run higher and usually warrant a cooler. I run an A (steeper impeller) which allows me to cruise at lower rpms (3-3500) and my oil temp stays pretty normal. I have a deep vee, light jetboat that will get squirrelly when going very fast in rough lake chop. A tunnel or larger boat that stays more stable can sustain higher speed for more water conditions and thus would have more rpms and oil heat if used that way. I would have to say its based on the type of boat, jet/motor rpm setup, and driving habits.
.02,
jd

I have no idea what my oil temp is running but I'm at about 140-150 on the water side. I figured because of the large difference between oil and water temps that I would try to bring down my oil temp. I added an oil cooler and have not had any problems. My motor is a stock fuel injected 350 with 120 hrs on it and I normaly run it wide open (4900-5000 rpms) for 15-45 minutes at a time, yes, minutes, that's not a typo. I obviously am no scientist/profesional as I don't even run an oil temp gauge, but I'm guessing a boat oil cooler is extremely efficient with the endless supply of cold water and the liquid to liquid heat tranfer vs. a non-marine engine that can only use air flow to cool the coils-Aluminum Squirt

Originally posted by DiverDown
I have a couple of friends/customers that have come to me over the winter and asked me to build them new engines for their jet boats...they both expressed concern that the motors they have seen run...all seemed to have very high oil temps and wanted to know what we could do to help this problem...I would like to know what kind of oil temps you guys are seeing in your boats and whether or not any of you are running oil coolers and large capacity pans to help the problem...
DiverDown,
Under full load, a jet pump causes the engine to hit a "stall speed," much like the torque converter of an automatic transmisson. Typically, this stall speed is somewhere between 4500-5500 rpm. Imagine moto-ing a car with a 5000 rpm stall converter, and your flooring it almost all the time.:rolleyes: The constant, severe load on the engine is the primary cause for the increased oil temperatures. Once fully warmed up, it's not uncommon for jetboat oil temperatures to exceed a whopping 300 degress F. Anybody that has an oil temp gage on their boat knows this, and most eveybody knows better than to estimate their oil temp by viewing their water temp gage.:o
Motor oil has several very important functions, including acting as a lubricant, as a seal, as a coolant, as a corrossion inhibitor, etc. All of these properties (and others) are diminished with its increase in temperature.
Some ways to combat this problem include:
-a hi-volume oil pump. This can include modifications to the block's oiling system for better oil distribution.
-a larger capacity oil pan. Most marine pans are a minimum of 8 quarts capacity; I myself run a 10-quart pan and my engine holds a total of 13-quarts with all my additional oil lines, filters, etc.
-heat exchanger. Not as common as the above mentioned components, but a very important one if you must combat a serious oil temp problem. I think more jetboats should be equipped with them.
-a good quality lubricant. Anybody that is apprehensive about running a synthetic lubricant specifically engineered for the application is probably not well educated in the area of engine lubrication, engine lubricants and their differing properties. As you are an engine builder, I don't believe I need to go into the details.
Anyone feel free to add to the list.:)
LO

Thanks for the info guys.
LakesOnly originally posted
-a good quality lubricant. Anybody that is apprehensive about running a synthetic lubricant specifically engineered for the application is probably not well educated in the area of engine lubrication, engine lubricants and their differing properties. As you are an engine builder, I don't believe I need to go into the details.
I build a lot of engines for the off-road guys around here that encounter some pretty extreme conditions including sustained RPM for long periods in 100 degree plus heat, and I can tell you that I have become a firm believer in synthetic oils and oil coolers in these applications.
I almost always use trap door type pans and run windage trays on the off-road deals. Do any of you do this with the boat set-ups?

Originally posted by DiverDown
Thanks for the info guys.
I almost always use trap door type pans and run windage trays on the off-road deals. Do any of you do this with the boat set-ups?
Marine pans are engine-orientation specific; it the engine sits forwards or backwards, the pick-up tube is placed accordingly to be aft of the engine...
Crankshaft rotational speeds can cause a roping effect on the crankcase oil much like a tornado looks, except horizontal and wrapped around the crankshaft...Since our engines are usually around 5000 rpm, most all of us run a windage tray and gated pan.
LO

I almost always use trap door type pans and run windage trays on the off-road deals. Do any of you do this with the boat set-ups?
I'm pretty sure most large capacity jet boat pans from either Dooley or Dan Olsen have both trap doors and windage trays