OMG 4.3 Liter Engine Problem Manifolds

[111torrance111]

I have a 1986 OMC 4.3 liter V6 engine that slightly over heated last season, I let the engine cool for a few minutes and started it back-up. The water seemed to flow again and ran fine the rest of the day, took it the marine and he suggested the annual water impeller repalcement.

repalced with a thru-hull aftermarket pump to make future replacement easiers on the OMC800 out-drive. When completed the new water pressure had blown the exhaust manifolds, I recently repalced both manifold anf now I'm having problems.

First Problem: The motor is missing and fouling 2 of the plugs.

Second Problem: The mainifold on the port side seems to build up water internally, I opened the release valve and the water drian out. it was also hot to the touch, The starboard side was cool & empty when opened.


Any thoughts on whats going on, compression is between 133 & 135 LBS per cylinder. Everything was fine prior to the impeller upgrade.

Thanks/Jerry

 

[chiefalen]

Re: OMG 4.3 Liter Engine Problem Manifolds

You have a 800 stringer ??? Would you be so kind as to post a pic of the drive first, the water pump upgrade.

We will go from there.

By the way the impeller does not have to be changed out except in rare cases every 4-5 years never every year.

Whats a rare case you may ask ? Say you hit a sand bar and sucked all kinds of sand thru the drive, then the impeller would be compromised.
Above is a example of a rare case. There are others.

 

[180shabah]

Re: OMG 4.3 Liter Engine Problem Manifolds

I think you meant OMC in your title, but OMG might be more appropriate.

When the manifolds were replaced, did you replace the risers also?

 

[chiefalen]

Re: OMG 4.3 Liter Engine Problem Manifolds

I never saw no water pump bypass the impeller in the drive it's fugazied.

Lets see what it looks like.

 

[111torrance111]

Re: OMG 4.3 Liter Engine Problem Manifolds

These paticular mainfolds are one peice unit, no risers to change out.

The new water pump simply connects to the front pully on the motor, one side goes to the Thru-Hull pick-up and the other side leads into the same input on the water pump as the original hose coming from the outdrive. The water exits the same normal path as before throught the outdrive. Apparently this was recommened on this older Stinger OMC 800 outdrive. It seems like nobody wants to work on them.

The pump seems to work great, I have plenty of pressure where it should be.

Jerry

 

[chiefalen]

Re: OMG 4.3 Liter Engine Problem Manifolds

It doesn't connect to the t-stat housing?? Never heard of this. How much pressure this pump put out, it didn't occur to you that this pump is gonna blow out anything. What is cooling your drive?? You figure sitting in water is enough?

Someone thought they are gonna redesign via a volvo or merc bravo sorta engine mounted water pump, they were originally designed the way they are.

Sir post a pic please so all these great mechanical minds here can maybe save you.

 

[Howard Sterndrive]

Re: OMG 4.3 Liter Engine Problem Manifolds

Apparently this was recommened on this older Stinger OMC 800 outdrive.

Sounds like your shop has some odd phobia about replacing impellers in stringer mount OMC drives.
Installing an engine mounted impeller was never recommended.
That's just a lot of me$$ing around to avoid a job that isn't all that challenging.
If you've never done one before it can seem scary, but an experienced tech should be able to do it without any difficulties.
There are some shops that don't even charge any more for omc impeller job than for mercs.

the new water pressure had blown the exhaust manifolds

that doesn't compute.. a rubber impeller can't "blow" cast iron manifolds...it's a non-positive displacement pump, only capable of building a couple bar of pressure.
hydraulics 101: "pumps don't make pressure, pumps only make flow. Restriction to that flow makes pressure"
I wonder if one of the old vanes from your original water pump is blocking a passage somewhere.
If they had done the job properly, they would see if a vane was missing and find it.

Everything was fine prior to the impeller upgrade.

no kidding... sorry someone butchered your boat.

I recommend putting it all back to original and replacing the impeller in your outdrive.

The water pump in the drive also cools the upper gear box in a stringer drive. Yours must be smoking hot with this new hull pickup.

 

[mthieme]

Re: OMG 4.3 Liter Engine Problem Manifolds

that doesn't compute.. a rubber impeller can't "blow" cast iron manifolds...it's a non-positive displacement pump, only capable of building a couple bar of pressure.
hydraulics 101: "pumps don't make pressure, pumps only make flow. Restriction to that flow makes pressure"
I wonder if one of the old vanes from your original water pump is blocking a passage somewhere.

I replaced the impeller in my Cobra last season. Immediately afterwards, I sprung a leak in the side of my PS heat exchanger and also had to tighten up some hose clamps here and there.
Maybe he just blew a gasket, maybe there was a thin area in the casting...22 years old...Pacific Ocean...

 

[chiefalen]

Re: OMG 4.3 Liter Engine Problem Manifolds

Theres some of the great minds i mentioned, Howard knows, it has to go back to the way it was designed.

I thought of doing all kinds of stuff and guess what i left it all original.

 

[Howard Sterndrive]

Re: OMG 4.3 Liter Engine Problem Manifolds

I missed the salt water thing - 20 years in salt could make blowable manifolds I suppose.Still can't troubleshoot something that is field engineered like that. Should be easy to put it back to normal.

Someone needs to photoshop an OMC logo into an OMG logo and sell decals on eBay.
I would like one for my tool box.

 

[Don S]

Re: OMG 4.3 Liter Engine Problem Manifolds

A couple of thoughts here on the engine driven pump. It may have been installed for other reasons than just so it's easier to change impellers.
Since this boat has been in salt water the water passages thru the intermediate housing at the trunions may have corroded away and now won't allow full flow of water to the engine. Instead of looking for a new intermediate housing, they could bypass it and use an engine driven pump.
Usually the engine driven pump is a high pressure/low volume type pump (more and shorter vanes) than the oem pump which is a low pressure high volume pump.
The high pressure pump (up to around 15psi at WOT) is still not enough to blow out manifolds and hoses if they are in good shape, but it would explain why the leaks showed up after installing it.