OMC 4.3 MANFOLDS. STILL RUNNING HOT

[Pedrocasas]

**** old boat issues were I ran the boat in the bay, rammed it up and the bellows on the starboard side burned to crisps from the inside. the manifold pipe flap was missing.***

new..
I replaced all the parts with used parts in good condition
I installed new manifolds
I installed a new thermostat and housing
I replaced all the gaskets
I bought new hoses.
all the manifold bellows new also

I took it out yesterday, I ran it no more than 15 mph,
after 25 mins it got to 250 degrees, and then the bellow from the starboard side blew again.
a lot of vapor. super hot.
manifold got so hot that the sticker burned off.


im not too familiar with this.
my guess is the boat engine is running dry?
what makes the water go into the boat??/ the impeller pump or the raw water pump? I did notice the raw water pump leaking a little.
also inside the manifold pipes, it was dry.

this time the boat overheated faster.

its a 1988 omc cobra 4.3

should I just call it quits and throw it away?

or should I try to locate the issue?

can it be a blockage or clogged that is preventing the water to get into the manifold?


does anyone have a diagram on how the water on this engines work??/

thanks again guys..

if anyone can give more support here is my email
unique.style.kustums @ gmail.com

thanks in advance guys

 

[bruceb58]

Did you change the raw water pump impeller that is located on the back of the drive?

 

[Scott Danforth]

As Bruce asked, did you replace the raw water pump impeller inside your drive? that is what pumps water to the motor

raw water pumps water from outdrive into transom housing, from there it is routed to the power steering pump, then up to the thermostat housing. from the thermostat housing, the block and heads are filled where the circulating pump circulates coolant and the excess water is pushed into the exhaust manifolds to cool them and be expelled with the exhaust. when the thermostat opens, it mixes some of its hot water from the block and heads into the water going to the exhast

your 1988 OMC would have had bat-wing manifolds. did you replace those with separate center-rise manifolds and risers? there is a reason they dont make new bat-wing manifolds.

 

[Lou C]

No Title

OK you need to check and replace your raw water pump which is in the upper gear housing in the outdrive under a plastic cover. The Cobra impeller is about the easiest to replace impeller there is. What you should have done, after the repairs, was to check the operation of the raw water impeller (since you already had an overheated exhaust system) when you first put the boat into the water. This could be done even just by backing the boat in still on the trailer, as long as you can lower the outdrive. Lower the outdrive to make sure the water intakes are under water. Then go up to the thermo housing and disconnect the water hose that goes from the transom mount to the thermo housing. Hold the hose straight up while someone briefly starts the engine, at idle speed you should have a column of water about 2-4" high according to my OMC shop manual. If your water flow is minimal, then you most likely have a worn impelller, wear plate, or bad water transfer tube gaskets in the lower gear housing. You need to carefully troubleshoot the raw water intake system. If you have an overheating problem with the engine, you should be bringing it back down to idle, as soon as you can and shut it off and get it towed in. If you keep doing this you are going to wind up with blown head gaskets and cracked cyl heads.

And while a lot of people keep pointing to the OMC batwing one piece manifolds, I had 3 sets of them over more than a 15 year period in salt water (each set used between 5-6 years) and I never had one problem with them, ever. NO water in a cyl, no gasket to leak like the older Merc and Volvo design and with a properly maintained cooling system, they ran from about 90-100* at idle and never got hotter than 135* even after coming off plane. If they were still available I'd get another set!

Unless yours are all clogged up with rust, they are not likely to be your problem, but they could have cracked due to the overheat.

Do the test I described and then report back.

 

[Pedrocasas]

Bruce: yes brother, I bought a complete impeller kit with a new housing, it came with a impeller, a metal type plate with a separate gasket of the same shape, a gasket for the housing, and a new housing. all brand new.

Scottt: I will be checking for clogs and blockages the way you explained how the water runs into the engine.

Lou: Im going to do the test you explained also. I did run the manifolds hot for about 5 mins or less. im going to double check if they are still good.

Thank you Guys.

I'll have more information and pictures for you guys.

 

[Maclin]

Have you tried to verify that it is pumping water using the muffs? I have read of instances where the shaft the impeller keys to has sheared off down below and is not actually getting driven by the drive gears.

 

[Lou C]

No Title

If your impeller is brand new, and if the gasket that goes in the plastic cover fits properly and does not leak, there are a few other reasons why a Cobra won't pump water:
1) if you had a bad overheat, the water tube gaskets in the drive, could be melted, because the exhaust passes through that area and if there is no cooling water the hot exhaust can melt them. To repair, you have to split the upper and lower gear housings, lift off the upper and replace the water tube gaskets. A rare problem I have heard of is a hole rusted through the water tube that can have the same effect.
2) on the transom mount there is a plastic nipple that the hose that goes from the pivot housing to the inner transom plate mounts to, this can crack and leak water.
3) in the impeller housing, there is a small vent that allows it to prime. It is hooked up to a rubber hose connected to a small nipple on the outside of the plastic impeller housing. If this is clogged it may not allow air to escape the impeller housing when the drive is lowered into the water. The way to test it is to remove that big plastic cover that is at the rear of the upper gear housing (3 bolts). Then lower the drive and hook up your water muffs. Disconnect that little rubber hose at the impeller housing. Have someone start the engine. There should be NO leaks around the impeller housing and a strong stream of water, coming out of that little nipple. If clogged blast it out with compressed air.

 

[Lou C]

http://www.crowleymarine.com/johnson...cfm?mdl=KK1PPB

water tube gaskets part # 75, part 76 is a plastic guide that guides the water tube into the lower gasket.
Only other things are a clog in the power steering cooler, you should back flush the hose from the transom mount at the thermo housing with the impeller housing removed, and have someone watch the pic of the mounting area I posted above, water should come out the side marked "out" If water flow is poor it could be pieces of an old impeller stuck in the P/S cooler...

to test the water tube gaskets, with the impeller housing off still hook up your muffs, have someone turn on the water and squeeze the muffs tight to the lower unit, water should spurt out the side marked "in". If no good, its either the gaskets, or there is junk in the water screen that is in the water intake area.

 

[Pedrocasas]

No Title

Hi Guys,
I was inspecting hoses to see if any had any clogs

I found this cylinder, looks like its connected to a power steering pump. I found out after all the oil spilled when I removed the small hose.

well this cylinder type of thing had 1 hose coming from the transom, im guessing from the impeller area.

I stuck my finger in there and noticed a lot of rubbery stuff.

I removed the cylinder and cleaned it out, seems to be pieces of old impellers.

Would this be a reason for the cylinder to clog up and don't let the water get inn?

thank you!!!

 

[Maclin]

"Would this be a reason for the cylinder to clog up and don't let the water get inn?"

Yup. Prime cause actually. Prior neglect with impeller flying apart and getting driven on though the system. That looks like the power steering cooler, usually first in line after the raw water pump. Hopefully that collected all the pieces. If not then it gets tougher because you need to backflush the whole system from usually the thermostat housing back.

 

[bruceb58]

You found your problem.

 

[Lou C]

Yep good work there. Remember, these open cooling systems depend on a lot of water IN and OUT to carry away the heat of combustion.Anything that interferes with the IN and OUT of water flow, will cause overheating....You might also pull off the thermo housing one more time, to see of any smaller pieces got in the feed lines for the exhaust manifolds....