oil

[nu2it]

I am rebuilding my mercruiser 140 this weekend and was wondering what the thoughts are on motor oil. would you use regular or mobil one on a fresh motor? All parts are new. this is a complete rebuild.

 

[SneakyPete]

I have always been told to break in a motor with good old dyno oil, then after a 10 hours or so, switch to synthetic. FYI, the guys who are building my stroker told me to stick with regular dyno oil for the life of the motor, but I will prolly switch to syn eventually.

 

[vinny p.]

There have been a few discussions on this here. My experiences have shown me that there is not enough benefit in synthetic oil to be worth the extra cost. Unless you are racing and need every last single horsepower. The worst thing you can do, is switch to synthetic after a motor has a few years on it. However, breaking in a new motor with petroleum then switching to synthetic is fine. It fact, its the only way. Manufacturers claim you can leave sysnthetic oil in for ridiculously long periods of time, mileage or hours. I know the oil doesnt breakdown as quickly, but doesnt fuel still get past the rings and end up in the crank case?? Then isnt that same fuel pumped through your engine?? I think it is..
When I used to drag race, synthetic is all I used. As I said before, every last horsepower.. I also changed it after every race day. But do we as pleasure boaters need that. Will a couple of horsepower make us any faster? No , it wont.
Being a mechanic for many years, I have never seen an engine fail because it had petroleum based oil in it. I have never said to myself, if this engine had synthetic oil, this wouldnt have happened.
Here is a few interesting things that have happened to me recently. Let me start by saying I dont do oil changes for customers at home. Too damn messy and not enough profit. I had a '98 Lumina with 80k miles, owned by a regular customer. She got the oil changed at some shop. They talked her into synthetic oil. 2 weeks later, I was swinging a new engine in for her. The synthetic oil loosened up the deposits in the pan, causing the oil pump pick-up clog. That limited oil flow, locked up the rear cam bearing, snapping the cam, stopping all oil flow. I know because I took the engine apart. Done, next motor.
This other case was just a few weeks ago. Same deal, synthetics were put into an S-10 Blazer with 65k miles. Almost immediately, a lifter tick developed. A change back to petroleum oil cured the noise.
Basically, if the engine is new, synthetics wont hurt anything. I dont see it being worth the cost, but its your call. You still have to change it as often as petroleum oil. But, if the engine is old, I have found, there is a real risk of damage. I am sure some of you have switched and not had a problem, maybe you were lucky or maybe my experiences were unlucky. Dont know for sure. I never did any lab tests, just sharing experiences.

 

[175checkmate]

I am in the same boat as Vinny. I have rebuilt engines and broke them in on regular oil and switched. Was it needed. Nope not really. The key to long engine life (This is me talking) is changing the oil on a regular bases. They experts tell us you can go longer on synthetic, I ask what about the fuel and dirt that always end up in the engine. Changing the oil at 3k helps flush this mess out.

 

[nu2it]

Thanks, I only conseder it because I know that a 4banger works harder than a 8. And I want this motor to last as long as it can. I will break in for 40hrs and then think about the change.

 

[JW]

Use the Merc 25W-40 oil, it's great for hard working stock motors.

 

[happy]

glad to see this oil ??? hasn't gone way off wack.. what i've learned is the base "stock" for oil has changed.. back in the older days frequent oil changes were neccesary because of the build up of (sludge) over a short period of time.. then came the epa... a base stock was developed that all the refineries had to use to make the product.. (oil) what happened here was that cars seemed to be using oil.. however the engines werent using oil, it was evaportating, creating voc's, which, the epa deemed exponential... albiet one car would only be nat on a windshield... take 300 million cars. and that added up... so now we have base stock two.. to eliminate the afformentioned problem..

as far as the marine environment goes.. i don't see the advantage of using synthetic... your boat is not your car, so its not driven as much.. condensation will always be a factor... yeah yeah i know it doesnt mix with synthetic oil .. zippedee... what happens when pure water runs thru your main bearings???

now when racing we use synthetic oil from the get go.. there is no break in time.. we pin the throttles and let em rip.. everything gets changed after every run.. and on ocassion... so does the engine..

 

[nu2it]

so is the quicksilver oil 25-40 good durring the break in?

 

[vinny p.]

Although I personally prefer straight weight oils, like SAE 40, for boats, that Quicksilver oil would be fine.

 

[boatman4021]

I agree with vinny. Synthetic cost too much for very little if any gain. I too like the straight weight oil's. If you are looking for an oil that holds up great under stress and heat, I found that Kendall high performance (racing) oil seems to be one of the best. I ran 50 weight Valvoline in my drag car for years and every time I would make a run and go back to the pit area, my oil pressure at idle would around 35 pounds from the heat. Before a run, it would be 70 at idle. One day at the track, I had an oil leak and lost a bunch of oil and I only had 1 qt with me (lesson learned). The only thing I could get my hands on was 6 qts of 40 weight Kendall so I used it. After the next run, I noticed my oil pressure at idle was still 60 pounds. I never stopped using Kendall after that day! boatman

 

[vinny p.]

Boatman,
I agree with you. When I first got into drag cars, I used straight 40 Pennzoil, never had a problem. I changed it after every race day. As with most of us, I am never satisfied with speed. Always wanting more is a real bad drug to be addicted to. When I made the jump to bigger power, I went to a full dry sump system with synthetic oil. Still changed it every race day. I am glad I got out of drag racing and into fast boats. Boats cost less and the thrill lasts for more than 9 seconds.

 

[JW]

The reason Merc has the 25W-40 special made for them is that it's a mixture of two straight weight oils. 25 weight and 40 weight. You get the best of both worlds, easier starting and more protection when cold with the 25W, then better heavy load/hot temp protection with the 40W.

 

[nu2it]

Thanks for the info. I always ran sae 30 or 40 I think I will continue to do the same.

 

[Chris E]

i run synthetic in my dads slug of a sea ray which also has a 140hp in it. i do it because it runs a fairly constant 3000 - 3500 rpms (when my brother in law has it it's right to the rug). anyway, i felt for a little more money it offers peice of mind and with that engine working so hard, i doubt its gonna hurt it any. i run Amsoil in all my car, van, boat whatever and i think it is good stuff.

as for break in, the 25w40 from merc is a good oil, but any good quality 40 weight will do the trick for you. Merc is funny, they send out a service bulletin saying not to use a multi grade oil and then sell you their "multi grade 25w40???" i no it's not 10w30 but i doubt the average consumer no's the difference.