your thoughts on mixing oil weights and longevity?

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Aug 12, 2002
here's my situation. Pulled the boat out of the water late November and winterized the engine while on land. I ran the motor for at least an hour and got it nice and hot then drained the oil. Replaced the filter and refilled with 4 or 5 qts of pepb boys proline 10w30 oil, and 2 or 3 quarts of pep boys proline 20w50. Ran the motor for about 30 minutes to an hour more to circulate the oil, then shut it down for the winter.

my question is this, will mixing weights like that cause the oil to not last as long? And I mean only in the sense that it's going to sit in the oil pan for about 6 months until spring time. The motor isn't running on it. What I do is use cheapo dino oil to winterize the motor for the winter. When the boat goes in the water come spring, I run on the winterizing dino oil for a few hours, then change it and refill with a quality oil (been using various synthetics last couple years) to go the rest of the season. Should I be concerned about running this oil for the few hours next year? From what I've gathered it's ok to mix oil weights as long as it's understood that you mix using the same brand (which I did) and also understand that the oil may not last as long as compared to using all 10w-30 or all 20w50 because their chemistries and additive packages may clash. Do you think, given what I've done, that the oil will be 100% come spring, or will it also break down more over the winter because different weights were mixed?

btw, I thought I had all the oil I needed but I didn't and wasn't about to run 10+ miles for proline oil. And the 20w50 has been sitting on the shelf for the last year so I was more than delighted to use it up

oh, and I know I'm talking about a boat here but it's really just a mixing oil weight question and I figured I'd get the most responses here. Thanks.

[ December 10, 2002, 01:23 PM: Message edited by: 1 FMF ]
What boat engine? I don't think you are in trouble. What brand of synthetic and weight are you going to use? You could have more problems with mixing the pro-line oil with the synthetic in spring. But then i doubt you will have any problem.
I like your plan.

But, I'd start the engine and run it for a minute to get your winterizing brew up in the head.
No problem with that type of mixing. Atually if all I was going to do was winterize, I'd use the thicker oil anyway.
its a Factory Ford Marine replacementmotor, 1993, 351w with GT40 heads, holley 4160 carb, 285hp.

I've got a 1992 Ford Marine v-8 engine that requires (per the manual) straight weight oils only. What synthetic do you use? I use Delo 400 sae30.

[ December 10, 2002, 04:19 PM: Message edited by: JonS ]
the boat is a 24' 1976 Apollo, formula thunderbird bought out the apollo corp. the following year so unless you know your boat history, it's a 24' Formula, deep-V hull, 24 deg deadrise I believe. The oringal motor was a Mercruiser model 233, which was a 351w with the rochester 2bbl carb rated at 233hp, with a Mercruiser I drive, 1.23:1 ratio. The motor was actually good until 1993, but I was having problems with the carb and distributor, and the exhaust manifolds were clogged and rusted onto the heads. So I finally said the hell with it, it was nickel&diming me to death with miscellaneous parts and fixes and was down more times than it was running so I went with a factory replacement motor, 351w HO from Basic Power Industries, out of North Carolina I think. Got the motor complete, with everything except exhaust manifolds, fuel pump, and ignition wires, for about $2800 I think. You can still find their ads in Offshore maggazine and other boating publications. Shortly after the new motor went in, the sterndrive crapped out. I bought a lemon Konrad drive- an aftermarket replacement for Mercruiser drives- from them also. But it only lasted one season, it had a warped lower housing that leaked water into the gearcase and could not be fixed, and Basic power would not honor the warranty. To this day I would give anything to meet somebody from Basic Power, especially the guy I dealt with on the phone, I can still remember the sound of his voice
. Anyway, traded the junk Konrad along with the original 1976 Merc drive for a new Alpha I drive (1.5:1 ratio) in 1995, and have been running that since. The next thing that needs replacing is the whole transom assembly, as it is over 25 years old, and the steering knuckle is shot. To replace that everything has to come off, so if it does then nothing less than brand new is going back on
Except for usual maintenance like oil, cap&rotor and a starter every few years the motor has been solid. I have to say Ford is #1 in durability for marine engines, especially the 351w. Only had to rebuild the holley carb this september, and also had valves redone last semptember but that was because I had a riser gasket fail and leak water into 4 cylinders. When I went to start it one morning I blew the head gaskets out, thankfully that was the only damage. But since I was pulling the heads off and was that far I figured better have the valves done. Just started using Redline lead substitute in it this year, along with doing oil analysis'. And too keep this sort of on topic
I sent in a sample of Redline 10w-40 that I ran all season in the motor, haven't gotten the results back yet from Terry though
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