oil pressure drops at 3500rpm only under load.

[470mercruiser]

Re: oil pressure drops at 3500rpm only under load.

Definetly not the origianl engine i just replaced it. Outdrive im thinking because the stickers dont match from the outdrive to bellhousing. the engine i took out was original as far as i can tell. So anyway i took out the oil pressure sender. When i shake it it rattles. Are they suppose to rattle?

 

[Don S]

Re: oil pressure drops at 3500rpm only under load.

What are the numbers on the decal. They used engine size back in 83, so that might be a hint as to what the gear ratio is.

 

[470mercruiser]

Re: oil pressure drops at 3500rpm only under load.

Which decals? There are no numbers on the outdrive.

 

[Don S]

Re: oil pressure drops at 3500rpm only under load.

I misread it, your stickers are on the gimbal housing not the drive. Find the ratio like I said before, then you will know for sure what you have.

 

[470mercruiser]

Re: oil pressure drops at 3500rpm only under load.



The number on the gimbal housing is 6252945. As you can see the stickers are differant.

 

[Don S]

Re: oil pressure drops at 3500rpm only under load.

Somebody replaced the drive. Impossible to say what it is without numbers. Wouldn't be the first drive replaced with something found on ebay with the wrong gear ratio. You are just going to have to check the ratio to find out what it is.

 

[fishrdan]

Re: oil pressure drops at 3500rpm only under load.

What you can do to find out what the ratio is, is to remove the spark plugs so you can easily turn the engine. Put the drive in gear, then turn the engine in the normal direction of rotation until the timing mark comes up. This will remove the free play in the shifting and start moving the prop.
Mark the prop so you know when the prop makes one complete revolution. Then turn the engine by hand and count how many turns it takes to turn the prop one revolution. It should take 1 and one half turns of the crankshaft to turn the prop one full revolution.
1.50 gear ratio.

Place a piece of masking tape across the prop and drive, then cut it so the prop will spin. This will make it easier to look at the prop and drive, while in the boat, to see when it's turned 1 complete revolution (line up the tape).

Oh yeah, mark the balancer's TDC notch with white-out or a white paint pen, on the front face, so you can easily see the TDC mark on the balancer.

 

[470mercruiser]

Re: oil pressure drops at 3500rpm only under load.

Ok ill look into that but right now my most important part is the oil pressure issue. Like i said earlier i took off the old sender and if you shake it it rattles. Didnt think it was suppose to do that. I got a new one. The new one doesnt rattle. I took the old one to work where i opened it up. connecting a ohmmeter to it and swept the thing in there by hand. It starts off high in ohms goes down to just about the end and goes back up in ohms again. Im hoping that is where i lose oil pressure. Im going to put on my new sender and cross my fingers. I couldnt find a mecahnical guage and i dont really have the money to spend to just use it once. A new sender is ok i probably could of used a new one anyway. Hopefully it fixes my problem and i can work on the outdrive problem. Kinda running out of time this year.


As far as i can tell there is only 2 ratios that have a 20 tooth drive gear.Its the right one i need at 1.50 ratio or one for a 4 cylinder at 1.98 ratio. What will happen if i run the 1.98 ratio? It should be like the rear end to a car right? One will give me quicker plane and lower top speed and the other will give me slower plane and more top speed. Am i right on this? can i keep the 1.98 if i have it or will it hurt anything?

 

[fishrdan]

Re: oil pressure drops at 3500rpm only under load.

So you are running a 23P prop and the engine is at 4800 WOT RPM(?), what it the boat's speed? (Use a GPS app on a smart phone if needed.) Also, what type of boat do you have, model size weight?

It sounds like the combination of a 17P prop that allowed the engine to turn too many RPM's,,, and the boat being driven over it's WOT RPM for a long time is what toasted the old engine. Heck, I had a 17P (5000' altitude) prop on my little 140HP 4 banger, at low elevation, and had to watch the RPM's.

I could see the boat using a 23P prop as there are boat's out there that will turn a 23P, even a 25p. "If" the boat is at 4800 RPM WOT, and the engine's recommended WOT RPM is 4800, I wouldn't worry about it. Though, I wouldn't run the boat at WOT RPM all day long and expect it to live a long and happy life.

 

[470mercruiser]

Re: oil pressure drops at 3500rpm only under load.

Without going this rpm too long i had 45mph on my speedo at 4800 rpm. I dont run it past 3500 most times because of the oil pressure problem. I still need a 25 pitch prop because my wot is suppose to be 4200-4600 rpm. Its a 1983 20 foot open bow formula 2. It weighs about 3000 lbs.

 

[fishrdan]

Re: oil pressure drops at 3500rpm only under load.

45MPH huh, well, I might be eating my words...

23P prop with a 2.0 drive running 4800RPM at 10% slip is,,, 47MPH. With 14% slip it's 45MPH.

Did you trim up the drive for max speed or was the drive all the way in/down and the bow plowing?

 

[470mercruiser]

Re: oil pressure drops at 3500rpm only under load.

45MPH huh, well, I might be eating my words...

23P prop with a 2.0 drive running 4800RPM at 10% slip is,,, 47MPH. With 14% slip it's 45MPH.

Did you trim up the drive for max speed or was the drive all the way in/down and the bow plowing?

d

didnt really pay attention too much about anything but the oil pressure and rpm. my speedo might be off too. ill get gps speed the next time i go out. i kept the trim down cuz the rpm went higher when i trimmed up.

 

[thumpar]

Re: oil pressure drops at 3500rpm only under load.

Well with a prop pitch of 23 at 4800rpm and a slip of 15% with the correct 1.47:1 drive you would be at 60mph. That would be pretty damn fast for water and you would notice it.

I think your old motor blew up because you have the wrong ratio and it overrevved. As for the oil pressure I would do as a previous post suggested and hook a mechanical gauge to it.

 

[470mercruiser]

Re: oil pressure drops at 3500rpm only under load.

I would love to get 60 out of this boat. Previous owner said he had 53 with the 17 pitch at 5000 rpm. Dont know whats going on with that i deleted his email so i can ask anymore questions. I dont have the money to get the right drive or even a mechanical guage right now. i got a new sender and im hoping that it was my problem. ill get it out on the water this weekend sometime and find out. Im pretty much convinced the motor blew because of the overrevving. I wish i had fixed that tach before and could still be running on the old motor. oh well i guess i learned a lesson. im looking for a 25 pitch to get me in the rpm that i need and ill look for the right outdrive when i can get the cash together.

 

[470mercruiser]

Re: oil pressure drops at 3500rpm only under load.

Well this is what i got today. 43mph on my speedo at 4600rpm didnt have it wide open. Drive trimmed up. Water very rough. Forgot my gps again. I had about 30psi at 4600 rpm. All i have done since last time is new oil pressure sender, changed the oil for sae 30 wt and a mercruiser oil filter. I think maybe my guage is screwy. I will get a mechanical and check it but dont you think running 30 psi at 4600 rpm wouldnt the engine make some noises? It runs great to me. I got up to 5000rpm full throttle with the drive trimmed up still no noises but didnt hold that rpm too long. Im going to get a mechanical guage on it soon to confirm everything is ok. I think it is fine just electrical. I hope it is anyway.

 

[Maclin]

Re: oil pressure drops at 3500rpm only under load.

...Previous owner said he had 53 with the 17 pitch at 5000 rpm...

53 KMH maybe...

 

[470mercruiser]

Re: oil pressure drops at 3500rpm only under load.

53 KMH maybe...

yea i dont believe anything he said anymore. im just gonna have to figure out things myself. I love the boat other than the oil problem and ill get everything right. I guess just not this season.

 

[470mercruiser]

Re: oil pressure drops at 3500rpm only under load.

Ok update on the boat. I pulled the motor and replaced the oil pump and screen. I set the pickup the best i could. I installed a new windage tray. Had it out today. Idles at a little over 20psi hot and wont go over 40psi at 4500rpm. I should be ok with that right? It doesnt go lower than 40 at 4500rpm.

 

[NHGuy]

Re: oil pressure drops at 3500rpm only under load.

I was thinking windage tray all through this thread. Their job is to keep the oil liquified at the pickup. Without the windage tray your spinning crank assembly is just whipping the oil and loading it with air. Sure it won't stay aerated for ever but it was doing it long enough to reduce your oil pressure as your rpms would rise. My 89 350 gets to about 40 psi above 3000 rpms with 10-30 oil. It goes up past 50 psi with straight 40W which I normally run during the summer. What weight oil are you running and did you look at engine temp, was it normal too?

 

[470mercruiser]

Re: oil pressure drops at 3500rpm only under load.

I was thinking windage tray all through this thread. Their job is to keep the oil liquified at the pickup. Without the windage tray your spinning crank assembly is just whipping the oil and loading it with air. Sure it won't stay aerated for ever but it was doing it long enough to reduce your oil pressure as your rpms would rise. My 89 350 gets to about 40 psi above 3000 rpms with 10-30 oil. It goes up past 50 psi with straight 40W which I normally run during the summer. What weight oil are you running and did you look at engine temp, was it normal too?

Im running rotela sae 30. engine temp is normal.