Oil and oil temp in 502 mag

[sleeper_dave]

I have a 27' Fountain with a 502 Mag. It has a little over 100 hours since a rebuild (rings / bearings / valve job / turned crank) last summer. I've been running the recommended quicksilver 25w40 since that time, with oil changes on a 20-30 hour interval. Engine has forged pistons, i get a little slap when cold. When i run it hard, i get some blowby and burn some oil. If i drive like an old man, i don't burn any. I haven't done an oil analysis yet, i'm still working on the logistics of getting a good sample out without contaminating it.

Is the quicksilver the best oil I can run? Is there another oil that will give me less blowby and oil consumption, and/or last longer? I'm open to trying synthetics, or other more expensive oils (not that quicksilver is cheap) if it means longer intervals or less blow-by. Is it important to stay with 25w40, or would a slightly different viscosity, or a straight-weight oil be advantageous? I run from April through October in MI, so the engine sees start-up temps from the low 40's to the high 90's.

Other question is oil temp. I have an oil temp gauge, it hasn't gotten past 160 all summer. Most times when i'm running, it will barely get to 140 (minimum reading on gauge). Is this bad? I know I don't want to run the oil too hot, are there consequences to running it too cold?

Thanks, and sorry if i'm asking the "same old questions". I still have some reading to do.

 

[Laminar Lou]

First off:

Now that is out of the way. Have you seen this device for pulling samples? I am not sure how your boat engine is configued but you can pull this through the dipstick. It's the only way to go even for a car if you ask me:

Extractor

If you are going to get an oil sample, get a "marine report"

Balckstone Marine report

After that, I would highly advise you send the report to Terry Dyson at Dyson Analysis. You have a very specific application and if you really want to get the best out of that motor, his consulting services are top notch (and very affordable).

Everyone here (including myself) is just guessing compared to Dyson.

 

[sleeper_dave]

Wow, i never saw that extractor. I'm going to have to order one. I'll be changing the oil this fall when i winterize, i'll send in a sample then and get the "dyson analysis" through blackstone.

 

[JonS]

Is this a Ford or Chev? I have a FGord v-8 in my skiboat, and all the marine tech say to use straight weights in the fords. I can't figure what the real difference is. May the lifter cams or such. Anyway most guys with the big blocks run straight 40 in Chev and Fords. Quicksilver is ok.

 

[Laminar Lou]

Quote:

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Wow, i never saw that extractor. I'm going to have to order one. I'll be changing the oil this fall when i winterize, i'll send in a sample then and get the "dyson analysis" through blackstone.

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I know other pumps exist, but the one from blackstone is well made and I use it for other things too. I've been known to use it for pulling power steering fluid out of the car instead of a turkey baster. The tubing is like $3 for a 25 foot section at Home Depot. Works like a champ.

Glad you are going to Dyson analysis. You won't be dissapointed.

 

[KBFXDLI]

I have a pair of 7.4L Merc Horizons in my SeaRay with the forged pistons/cams/crank and they all sound like a bucket of bolts when you start them until the pistons expand to tolerance. I run the quicksilver 25w40 with fine results but I have seen some guys run Pennzoil Marine 40w and it works ok too. If you are running a go fast boat, I think I would try the 40w or maybe a 20w50. But, just make sure you let that motor warm completely before you get on it.

 

[Brett Miller]

It it was mine, it would have Amsoil 20W-50 or Mobil 1 15W-50 EP.

 

[1 FMF]

Quote:

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I run from April through October in MI, so the engine sees start-up temps from the low 40's to the high 90's.

Other question is oil temp. I have an oil temp gauge, it hasn't gotten past 160 all summer. Most times when i'm running, it will barely get to 140 (minimum reading on gauge). Is this bad? I know I don't want to run the oil too hot, are there consequences to running it too cold?

Thanks, and sorry if i'm asking the "same old questions". I still have some reading to do.

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the temperature at which you start the engine will dictate whether or not you'll want a multigrade oil like a 25w-40, 15w-40, 5w-40 or 20w50 versus a straight 40 or straight 50 weight oil. The 15w-40 oils are most easy to get and least expensive, and they are good oils. Chevron delo 15w40, mobil delvac1300 15w40, and rotella 15w40. The synthetics in 40 weights are 5w-40: mobil 5w40 if you can find it or rotella 5w40. Everyone will attest the mobil 5w-40 is a good oil. Any multigrade oil, 25w and lower, will be fine for any starting temp. A cpnventional petroleum monograde 30 oil is ok down to around 40F, a monograde 40 oil around 60F, and a mono 50 I don't know but expect it to be >= 60F. Expect a "synthetic" monograde to be ok to lower temperatures.

The temp the oil reaches when the motor is running dictates what viscosity you should run: 30, 40, or 50 weight. 40 weight is the norm for boat motors, hence the recommended mercruiser 25w-40 oil. If you're oil temp gauge is registering at most 160F then something is wrong! Either the oil temp gauge or the oil cooling/water cooling setup on the engine. If the oil is only getting to 160F that is bad and a recipe for nitration and oil sludge, especially if you know you have blowby!
A quick fyi on oil temps: too cold = nitration, and add fuel, water/moisture, and combustion byproducts = nitration, acid, and oil degradation. Too cold is anything less than a temp and run time to burn off water and fuel/combustion byproducts, ballpark typically < 200F. Then there's also too hot, ballpark > 200F which equals oil oxidation and vaporization, decreased viscosity, and oil degradation.
The oil temp you want to shoot for is 180-220F. That way you have the viscosity that's intended, contaminants get burned off and the oil stays clean and lasts long, and it's not too hot where the oil oxidizes.

Even with coolant temps in the 140-160F range, your oil temp should hit 180F+ after 15-20 minutes running at 3000-4000 rpm. I would first suspect an inaccurate oil temp gauge. When you had the engine rebuilt, was there any mention of a dirty oil pan? If you're oil temps were that cold and you had a decent amount of hours on the motor I would think there would've been some evidence. However if you were religious on frequent oil changes then you may have prevented that problem from getting out of hand.

I would verify oil temps somehow and be sure of the reading. If you're typically 210-220F and lower all the time then a 40 weight would be fine. If you plan on running high rpms' and long periods of time, the oil will run hotter and you'll want a 50 weight oil so the viscosity is there at higher temps. And if you know the engine runs rich and the oil is diluted with fuel from blowby (oil analysis) then you'd want a higher viscosity oil (50 weight) to generally help offset the decrease in viscosity due to fuel dilution.

Also look into where your oil temp gauge is taking its reading, and do you have an oil cooler and what temperature cooling water is supplied to the cooler? Maybe the oil temp guage is correct depending where it's taking it's reading

 

[Ryan02SS]

1 FMF covered about every aspect to your question very well.

160 is too low for sure. I have large 3" Mercrusier oil coolers on mine and the temp stays 180-190 cruising speed and 210* after a min or so WOT. I run a 140 Tstat and it normally keeps the water temps 148-150*. This is mainly to help stave off detonation as i'm running 10.4 compression.

It sounds like a gauge problem to me. I would check the wiring, gauge and placement of sender. Oilpam is best for the oil temp.

I used Mobil Delvac 15W-40 in my last 360 SBC with nice results. It seemed to hold up well in that 400hp engine.
My latest 355 SBC should be edging near 450hp I intend on Amsoil Syn 10W-40 or Redline 10W-40. It's a fully forged shortblock that I feel will benefit from the Synthetic.