Grog

Conclusion: The stock Merc oil cooler cools the oil about 30-40° for WOT conditions.

Here's why I think this:
I was having a problem with condensation under my valve covers so I installed a Gaffrig oil temp gauge (sender in the remote oil filter mount). Sure enough, my oil temps would only reach 210° after a long WOT run. As soon as I backed off to cruise it would drop to 150-160°. I like oil temps a little warmer than that.

Before plumbing in an oil t-stat, I decided to bypass the stock Merc oil cooler to see just how much cooling it provides.

Results: Peak and level off at 240-250° during a WOT run. 180° at cruise. This is right about where I want to be. Everybody agree???

Strip Poker 388

iTrader: (6)

No I dont agree.

My oil thermostat is set at 210. I can see it climb to 210 then open and go down to about 185-190. At this temp i would think it would help on the condensation . It takes a while to get the oil temp up. i Wait till 140 to go over 2800rpm.

blue thunder

I like oil temps to not exceed 230F after wot. Cruise at about 200-210 is ideal. 250 is too hot for longevity of engine and oil.

BT

Grog

Funny thing....I can't find anything on the internet where oil manufacturers provide a maximum safe temperature rating on oil.


388 -
According to a thread response submitted by Dennis Moore, oil needs to get to around 220°F to burn off condensation which makes perfect sense since water boils at 212°F.

I agree that oil kept at a higher SUSTAINED temperature will lose its lubricating properties sooner than oil at lower temperatures. But, I also believe that for a boat motor, normal oil temps of 160°F to 200°F (cruising) along with the ability to heat the oil above 212° (relatively short 240° to 250° WOT runs) might actually be better for the oil than always running 150° - 190°. I don't know what temp oil is safe to, but I am willing to bet that it is greater than 250°F. Especially when it is changed every 30 hrs.

Just my uneducated opinion....

Greg

Lmarth

For what it's worth, in a prior life when I was flogging big block chevies on the road racing courses in the notheast, GM said 300 degrees max measured in the pan. Now don't misinterpret that. Obviously, you'd size your oil cooler and ducting to maintain roughly 200-220 degrees, but if it spiked to 300 for whatever reason with the conventional oils of the day, you were in big trouble. I'll spare you those war stories. I would not ever want to see 250 degrees with my boat and I don't, even with the blowers.--Lou

mikes280

run the oil between 180 and 220 and run a pcv system to keep down on the condensation it works merc. does it on some of there motors we have been doing it for ten years and unless you have a leak like a headgasket you will not see the mosture.

Reed Jensen

My understanding is oil reaches it's maximum "lubricity" at around 200 degrees... according to the tech guy at Aviad ( they make external belt driven oiling systems for race cars and airplanes ) that whenever your oil comes close to boiling ... app 200 to 212 that most of the moisture will turn to vapor and leave... but.... if the block is running much cooler... such as an offshore boat that never gets above 150 (water temp)... that the vapor will condense in the valve cover and look like glop... so ... it isn't so much just oil temp that needs to be regulated. I guess if a few hot runs get the oil up to 240 to 250 you will definately get the water out of the oil... My understanding is regular dino oil is okay up to 350 before it begins to break down..

blue thunder

Mobil 1 synthetic calls out 325F on the back of the qt jug as a max temp. Not sure what the breakdown point of dino oil would be, but can tell you when I took straight 30wgt dino oil to 280F last year I ruined the mains in two engines simultaneously. I still had the oil temp problem after rebuilding and made sure I backed off when the temps got to 250F. Tore the engines down again after that and had some minor scuffing. This year I have solved my oil temp problems and it doesn't go over 230F. Later today I will have one of those engines on the stand and I will see how the bearings look. I already cut open the filter and it was clean.

Really there is no magic number other than the oxidation point at which oil starts to turn to its carbon state. That is probably the 325 number M1 speaks of. This temp is way too high. Oil viscosity can be charted linearly. On a chart the viscosity will drop as the temp rises. It will also loose its cushioning ability at the viscosity drops. Add this loss of cushion to each internal bearing clearance within an engine. The bearing with the largest clearance will begin to scuff first because the journal moves around more. The bearing that shows tighter tolerances will be happier at the elevated oil temp. Problem is, at startup with st 40, 50 or 15-50, this tight bearing may not get good flow distribution of oil and the bearing will suffer.

I believe if you built an engine to run specifically at 275-300f you may be to successful. Problem is, most of our marine engines are not built that way. So it is really not so much a matter of what the oil can take as it is a matter of what an engine can take with the clearances it runs. I can say with my method of clearancing an engine (.001 per inch of journal) 250F is as high as I will go. Build them tighter and you can probably go higher than 250F but will suffer in other areas.

BT