omc overheating only on plain

[makingufast]

i have a 1986 mark twain 210 with a 350 omc engine and a omc 800 outdrive. and boy do i need help big time....... i have tried everything i know and then some... my boat overheats only on plain. it will sit at 160 all day long. as soon as i gas it up and get it up on plain the temp starts climbing to 220 i bring it back down to 1200 rpm and it come off plain and runs fine temp slowly comes back down to 160.

new thermostat, new front water pump (engine), impellar appears to be good, exhaust manifolds are pretty clear.

i need some major help and advice before i just sink this thing.

thanks for looking
brian

 

[Philster]

Re: omc overheating only on plain

Check the flow coming in from the drive hoses.

 

[Bifflefan]

Re: omc overheating only on plain

impellar appears to be good, exhaust manifolds are pretty clear.

brian

Replace the impeller anyway and pull the hose inside the engine compartment and see what kind of flow you are getting. If its good, then look to the manifolds.
Im guessing that they are plugged some what.

 

[Brentathon]

Re: omc overheating only on plain

I have a similar issue with my 5.7 merc, the flow coming in seems to decrease as I go up in rpm. the incoming flow seems to be less when on plane......I feel your frustration.

 

[CayugaCobalt]

Re: omc overheating only on plain

I have the same situation with my 2000 Volvo 3.0 GS.

I installed clear vinyl tubing downstream of the raw water impeller and upstream of the thermostat. This allowed me to see there were no air bubbles sucked in, but one could not really judge if the flow was increasing or not, it was just a solid rod of clear water.

How would you judge flow change?

 

[Brentathon]

Re: omc overheating only on plain

Yes, I agree that when the clear hoses are full of water without bubbles, there's no indication of flow.......not so easy.
My clear hoses coming from T-stat that diverts the excess water straight out to the elbows were mostly filled with air, allowing me to see the small amount of flow coming out of the little check balls.

 

[Howard Sterndrive]

Re: omc overheating only on plain

impellar appears to be good,

at least 3 hours work to access a $20 rubber part and you didn't put a new one in?


it doesn't take but a trickle of lake water to keep an idling engine cool when it is making 5HP to run the alternator

you need a hydrant load to keep it cool when it's making 200+HP runnin down the lake

 

[HT32BSX115]

Re: omc overheating only on plain

you need a hydrant load to keep it cool when it's making 200+HP runnin down the lake

Absolutely! ANY little obstruction to water flow can cause an overheat at high power settings!

The water MUST go from the raw pump to the T-stat housing, some into the engine (depending how "open" the T-stat is), then to the manifolds, risers and then out.

If it is restricted ANYWHERE along that path, you can get an overheat! It's really fairly simple thermodynamics. Water has specific, measurable heat transfer characteristics. a specific amount of water must pass through the engine at a given power output to maintain a particular temp.



Regards,


Rick

 

[makingufast]

Re: omc overheating only on plain

bifflefan- your the ssecond person that told me to pull the main hose off and check the flow..... but if it is only happening once i am up on plain. so if i have good water pumping at idle then i should have better water at high rpm ? should being the key word there?

 

[HT32BSX115]

Re: omc overheating only on plain

bifflefan- your the ssecond person that told me to pull the main hose off and check the flow..... but if it is only happening once i am up on plain. so if i have good water pumping at idle then i should have better water at high rpm ? should being the key word there?

You MUST have a LOT more water flow at RPMs above idle or you WILL have overheats.

Installing a clear hose between the transom and the engine (raw water supply hose) and disconnecting it to observe water flow will tell you 2 things:

---How much flow you have at various RPM

---And whether or not there's air bubbles in the water going to the engine.

You MUST do this test with the boat in the water. Doing it with "muff" won't tell you much because you cannot get anywhere near the same amount of water though a water hose.

 

[makingufast]

Re: omc overheating only on plain

ah thanks HT.

 

[KRH1326]

Re: omc overheating only on plain

I don't know if the 800 is physically similar to my electric shift. I had struggled to locate the cause of an over heating (planing only).

Long story short, that clear hose helped me determine that when i was high rpm, exhaust was pushing through the swivel seal and getting pulled into the impeller, right where the pick up tube meets the housing.

Again, I don't know if they are similar, but I have a grease fitting, right at the leading edge of the leg, right at the swivel housing. I was able to shoot grease in, which re-packs that seal. It got me back to mooring, and it got me to the docks, so I could properly make the seal repairs.

 

[Howard Sterndrive]

Re: omc overheating only on plain

Again, I don't know if they are similar, but I have a grease fitting, right at the leading edge of the leg, right at the swivel housing.

his is identical
somehow I read he had greased it - but I don't see that now

http://www.youtube.com/watch?v=rWFf2Y1okb0

 

[KRH1326]

Re: omc overheating only on plain

his is identical
somehow I read he had greased it - but I don't see that now

http://www.youtube.com/watch?v=rWFf2Y1okb0

Nice video, but there's no vids for E-Shift. Not Fair ! It's a conspiracy, I tell ya !

 

[makingufast]

Re: omc overheating only on plain

that seal has never crossed my mind. or anyone that i have questioned about this boat.. i will put it all back together tomorrow and try it out. i have the lower unit apart (again) is that seal easy to find, i will replace it now while it is all apart.

thanks again
B.

 

[Howard Sterndrive]

Re: omc overheating only on plain

the seal is in the base of the exhaust housing. The grease does the sealing, the lip seal keeps the grease in

 

[studdy05]

Re: omc overheating only on plain

Actually there are two seals in that swivel housing and they need to be in good shape to hold the grease in. I'm having the same issue. I've got mine apart now and am fully resealed, greased, half a dozen impeller rebuilds, new risers, new manifolds, new water pump, two new thermostats and new head gaskets. I have a thread that's been three years in the making over this issue so I consider myself somewhat of an expert on the cooling having spent maybe $7,000 chasing it down. Right now I have the heads off being descaled. Scale won't allow water to transfer energy to the metal properly. I'm hopeful it's the scale in the heads but not optimistic after three years. I'm tempted to buy another boat omc 800 chevy 350 as a clone and swap parts back and forth just to figure out where the problem is. Or at least what section. This has obsessed me for three years. When I find it, I'll likely post it in the new York times and on billboards across the country.

 

[studdy05]

Re: omc overheating only on plain

FYI I've even added an electric sea water pump into the system that I can kick on at high rpms. I've also installed a NASCAR type high volume water pump that pushes 30% more water through the system. The head gaskets restrict flow quite a bit. I'm using the Felpro marine head gaskets and after studying it for a while I'm considering trying others. I can't reproduce the overheating unless I'm under a load. With the outdrive off, and water hose feeding the engine, I can turn 4700 RPMs at 140 degrees for one hour when the ambient temp here is 100+. It's got to be under a big load to make the temp spike. I've been all over the engine with laser temp readings. Nothing helped.

 

[makingufast]

Re: omc overheating only on plain

ok trying to find these seals for the swivel housing.... anyone know the part numbers ? or where to find them with out ordering the whole housing....

 

[studdy05]

Re: omc overheating only on plain

I use amarket marine. Call them and tell them what your after. It's inexpensive.

Www.amarket.com and it has an 800 number on the website.