Need info on 99' 300 Promax

[hydrostreamin!]

What can you tell me about a 1999 300 Merc Promax? Pros/Cons? Any info will help me. Looking at a boat with one on it.

[HP]

I have one on my 21 Liberator. It does use alot of fuel compared to the newer X motors. Very dependable with steel sleeves. If you are still running the oil injection......remove it! You'll be glad you did:D Good luck, be safe, and have fun:D :D :D

[fishead1]

Running twins totally stock never had a problem.

[jerry]

Jerrys Opinion , One Of The Best Motors Merc Ever Made !!!!!!

[hydrostreamin!]

I have one on my 21 Liberator. It does use alot of fuel compared to the newer X motors. Very dependable with steel sleeves. If you are still running the oil injection......remove it! You'll be glad you did:D Good luck, be safe, and have fun:D :D :D

Thanks for all the info guys. It seems you highly recommend removing the oil injection. Why so?

[Dean Dorsey]

Many guy do it for safety reasons. The promax 300 I don't think has had any higher failure ratio than other oil injection systems out there, but it is mechanical and if I remember correctly with a plastic impeller, mechanical things eventually fail either sooner or later. If this goes it will take the whole motor with it before you realize what has happened. Better safe than sorry philosophy.

[HP]

If my memory holds....there is a plastic gear on the crankshaft running against a steel gear on the oil pump. I know there's alot of motors out their that still run the oil pumps. One thing for sure if you put the oil in the gas you know it's getting oil. At idle up to approx. 3000 RPM (with oil injection) your not getting but maybe 100:1. As with most of us you probably run your boat pretty hard. Well........that means the first 150 to 200 feet you are not getting 50:1. It works for me to know I'm getting the proper mix all the time.;)

[hydrostreamin!]

If my memory holds....there is a plastic gear on the crankshaft running against a steel gear on the oil pump. I know there's alot of motors out their that still run the oil pumps. One thing for sure if you put the oil in the gas you know it's getting oil. At idle up to approx. 3000 RPM (with oil injection) your not getting but maybe 100:1. As with most of us you probably run your boat pretty hard. Well........that means the first 150 to 200 feet you are not getting 50:1. It works for me to know I'm getting the proper mix all the time.;)


Thats a very good piece of info to know.

[Dean Dorsey]

HP is correct it is a gear not an impeller, I knew there was a plastic part I was suspect of, that was it. I will play devil's advocate for a moment. For many years people have been saying the same thing on all oil injected outboard motors, pull the pump and mix. In the days of OMC's VRO-1 systems it made great sense as they were prone to fail and I pulled mine as well. The absolute safest thing to do is pull it and mix if you do it right every time. Since that time I have had a few 2.4BP's and later 260's which gave you no choice you mixed. I went to the PM 300's a few years ago and would not go back to a mixed motor short of competative racing for anything. First it is a hastle to mix, if you are mixing at a gas station mixing correct ratio's and more importantly making sure it is fully mixed by the time you launch can be a problem. If you do it out of cans like I always did have fun and your arms will get real strong from pouring 5-10 gal. containers constantly. Next if you are a pleasure/ weekend warrior like many of us you will do a fair amount of idle 4-6 mph cruising, at 32:1 it was a mess usually fouling plugs, and you looked like a smoke bomb doing it, if 50:1 is where you would mix yours, it would be a bit better but I would think it should be closer to 40:1 for safety even at lower 6K rpms. The mix ratio is what it is to allow you to safely go WOT, you use more oil than you need pre-mixed at anything less. So less oil consumption is another plus of oil injection, if you run synthetic it's not cheap $23-50 per gallon, if you go through 60 galons per weekend like I do it costs considerably more to mix over a season and I don't want the headache. I have owned 3 of these motors in the past few years and 2 have gone down, but not from oil injection failure or anything related, rather as a result of not monitoring mods close enough. I know of a few pumps that have failed and for that reason many will pull them, for me it's worth the small risk. It is a personal issue, as a non racer I would not pull it as these are very reliable motors if left alone. One bad load of fuel and about 20 other things will take it down just as quick. In the past I found myself spending more time worrying more about what might go wrong and trying to prevent it than having fun and yet they still went down from one of the other reasons. That is the beauty of this motor you don't have to worry, put good gas and oil in and go. Just my .02

[22VelocityProMax300]

I used to own a pro max 300. I had the opportunity to talk with an engineer up at Mercury Racing, basicaly what he said the plastic gear you will not have any problems with if you maintain the redline at 6200 rpms. It was up at 6800 rpms the gear would fail. I ran mine with the stock impeller for about 150 hrs and never had a problem. frank