Mixing multi-weight oil with straight oil

[mcmnswj]

My 5.7 litre Merc on my 23 Wellcraft Midcabin puked all her oil into the bilge during her shakedown cruise Memorial Day weekend due to an extra oil filter rubber gasket that was left behind last fall. (My fault, I changed it). Anyway, the marina staff was kind enough to have a nice gentlemen dinghy out 4 quarts of 10W 30. I have always used only Mobil One HD30. Beggars cant be choosers so I added what he brought me and started it up, found the problem, shut it off, had him tow me back to the marina where I changed the filter but NOT the oil and found the extra gasket sitting right on top. The next day I filled her back up with straight 30 weight oil and ran the boat for about 30 minutes with family on board. My question is this: have I caused any damage thus far by mixing 10W 30 and straight 30 weight oil together? Should it be changed entirely before I start it up again?

 

[Haut Medoc]

Re: Mixing multi-weight oil with straight oil

Welcome to iboats <br />You didn't do any damage, but I would replace the oil with the 30 weight.......JK

 

[mcmnswj]

Re: Mixing multi-weight oil with straight oil

JK,<br /><br />Thanks for the quick reply. Breathing easier now. I will change the oil.<br /><br />Joe.

 

[HT32BSX115]

Re: Mixing multi-weight oil with straight oil

You won't "hurt it", per se'<br /><br /><br />This was from Chevrons Automotive oil FAQ:<br /><br /> Can I mix different viscosity grades of motor oils?<br />Yes. It is always advisable to not mix motor oils, however, different viscosity grades of the same motor oil are compatible. Be aware that mixing viscosity grades will turn out a product that is different in viscosity than either what was originally in the engine or what was added. <br /><br /><br />This was from CITGO's FAQ<br /><br /> Myth: You can't mix brands of motor oil.<br />Fact: Mixing brands is not the best practice because the additive systems in each may be different and when mixed may not function as efficiently as desired. However, no serious problems will occur if you must add a different brand of equivalent quality between oil changes. It is very important to maintain proper oil level. <br /><br /><br />It appears that it's ok to do in a "pinch"<br /><br />And this was excerpted from the "The engine oil <br />bible"<br /><br /> Marine Oils.<br /><br />I sometimes get asked "why are marine engine oils so expensive and why can't I just use regular motor oil in my marine engine instead?". Well, the National Marine Manufacturers Association Oil Certification Committee (click here for more info) introduced a four-stroke engine oil test and standard called the 4T certification. This specification is meant to assist boaters and manufacturers in identifying four-stroke cycle engine oils that have been specially formulated to withstand the rigors of marine engine operation. The certification was prompted by the growing influence of four-stroke engines in the marine market and their unique lubrication demands. So the simple answer is that regular road-based engine oil products don't contain rust inhibitors and won't pass the 4T certification. Lakes, waterways and the sea is a lot more aggressive an environment for an engine to operate around than on land.<br />Note : the NMMA have long had a similar specification for 2-stroke oils destined for marine use, called the TC-W3® certification. <br /><br /><br />So it appears that you should be using one of the following type oils or equivelent in your 4 stroke powered boat.<br /><br /> http://nmma.org/certification/programs/oils/fc-w.asp <br /><br /><br />Regards, <br /><br />Rick

 

[Mischief Managed]

Re: Mixing multi-weight oil with straight oil

Better than the alternative... I would not worry at all.

 

[KRS]

Re: Mixing multi-weight oil with straight oil

Change it an go on!

 

[thunderroad]

Re: Mixing multi-weight oil with straight oil

One time when I checked the oil in my daughter's car it was a little over 2 quarts low. I asked her why she hadn't put any in. She said she forgot what kind to put in. I told her that in a pinch, look for these two words on the can.....MOTOR OIL....fill it up, save the can and show it to me.

 

[crazy charlie]

Re: Mixing multi-weight oil with straight oil

If you dont want to change it right away ,you can just add some Lucas oil additive or some STP.That will thicken it up enough.