Over Heating

[nate44]

I have a 1968 John Allmond with a mercruiser straight 6 cyl.
The manifold gets way too hot.
Here is what I have done:
New impeller in the outdrive
Took water pump off engine. metal impellers look fine and it spins on the shaft fine. no excessive play and does not leak.
Ran motor with new thermostat and without thermostat
Water is running to the manifold and is coming out my outdriver hub.
I have taken the manifold off and have run water through it and it seems to flow fine.
Question is what is making it so hot that it boils spit?
Do I need a new manifold? sure hate to spend the money when it is no necessary

HELP!!!!!!!!

thanks

nate

 

[Haut Medoc]

Re: Over Heating

Is this a raw water (standard cooling) or closed system?....​

 

[nate44]

Re: Over Heating

It is raw water. The water coming out of the hub is normal exhaust temp
It seems the rear 2 exhaust ports are the one that are reaaly hot.
Dump question. The exhaust ports should be water tight right? otherwise water will get in the block?

Nate

 

[HT32BSX115]

Re: Over Heating

If I'm not mistaken,

That manifold (if original) may be aluminum (my 1966 150 Merc I-6 was) There's also an aluminum plate inside that is only about 1/4" thick (when new). If you're raw water cooled and the manifold and/or plate has never been replaced you may have a corrosion clogged mess inside. If it's the newer cast iron model the same may apply.

Doug Russell has those manifolds I guess... You can go look at the price....I almost think the prices are misprints! Both the aluminum and cast iron manifolds are something like $2600.

There are aftermarket manifolds that are MUCH cheaper. I think you have to go to a manifold that fits the later 165hp I-6 (250cu-in gmc) engine..... and then get the elbow and plumbing that will adapt.

I had the exact same problem with the 150. It was the raw-water pump. (you said you replaced?) If you ran it even for 30 sec dry, you may need to replace it again.

Also, you may have debris from the previous failures or other debris in the system.


There is no path at the exhaust port for water to get in. The only place where water could get into the exhaust (in a good condx manifold/riser/elbow) is if it rises up within the elbow from the outside. There's usually a "flapper" to prevent that. The "riser" is well above the waterline for that reason (hence the name "Riser")


More. If that's an aluminum manifold (like my 1966) and that 1/4" plate has corroded thru, water will get where it shouldn't.

If you even think the manifold is bad it needs to be replaced. Is it a salt water boat?




Regards,


Rick

 

[nate44]

Re: Over Heating

It is a cast manifold. I called OSCO and they have them for $453. How can you tell if a riser is bad? or do I just buy a new one?
Should I go ahead a just replace my water pump as well?

I guess if I do all that everything will be new. Can anything else cause the over heating?
Sure didn't want to dump another $700 in this old boat!!!!!!!!

Nate

 

[Haut Medoc]

Re: Over Heating

It is a cast manifold. I called OSCO and they have them for $453. How can you tell if a riser is bad? or do I just buy a new one?
Should I go ahead a just replace my water pump as well?

I guess if I do all that everything will be new. Can anything else cause the over heating?
Sure didn't want to dump another $700 in this old boat!!!!!!!!

Nate

Before I did anything, I would disconnect the raw water inlet hose & see what kind of volume you are getting from the impeller......
No more than 20-30 seconds though or you will fry the exhaust bellows....
Next would be to plumb in a short length of clear hose & look for excessive air bubbles.....
If water flow in appears OK, then it is time to check how the water gets out......
If you are convinced that the engine circulating pump is OK, move on to the manifold/riser....
Pull them apart & look at them....
The water dumps in the riser may be partially clogged with scale & impede water flow......

 

[HT32BSX115]

Re: Over Heating

When you say "Cast" I am assuming you mean cast IRON. If it's the older cast Al model you should look it over very closely and if it IS the Al model you'll want to switch it to OSCO (or equiv) cast iron.

Of course, you do need to follow Hauts advice first. You must know if the pump and flow are adequate.

 

[Bondo]

Re: Over Heating

Ayuh,....

Is this something New that Just happened,..?? or does this issue have some History,..??
When you replaced the Impeller,.. Were there Any pieces missing,..?? Did you Find them,..??

There's also a way of rerouting the cooling system to relieve Hot Spots in the manifold on those old I6s,....
Fishermark just did his Dad's, with directions from Achris,... Maybe a couple of months ago.....

 

[nate44]

Re: Over Heating

Thanks for all the info.
I just ordered a new water pump from Advanced Auto.
I am getting water in the manifold and block because when I remove the brass plugs water is coming out. I took my end caps off and it is clear end to end.
I nam hoping that my water pump was on the fritz and not pushing enough water!!!!!!
I will reply after I put my pump on

Thanks again

Nate

 

[nate44]

Re: Over Heating

Bond O
I just bought the boat and yes the impeller was fried and some small pieces were missing
Has it been a history???????

nate

 

[Bondo]

Re: Over Heating

I just bought the boat and yes the impeller was fried and some small pieces were missing

Ayuh,.......

1st order of business is to Find the Missing pieces......
They're probably stuck somewhere between to Impeller pump,+ the T-Stat housing......

 

[ziggy]

Re: Over Heating

They're probably stuck somewhere between to Impeller pump,+ the T-Stat housing......

yep, what he said..... go look for pieces of impeller. yer likely to find many peices. at the very least, flush from ft. to back and back to ft. with the hose disconnected from the tstate. and the lower and upper seperated. i used a bucket to catch the water at both ends and ya wouldn't believe how much impeller i flushed out. don't know if ya got yer tstat back in or not. but do put it back. my guess that w/o it would make the back of the engine hotter than the ft. where the water enters the system.
don't know how ya'd tell. but could be impeller pieces have made their way into the block too. possibly blocking cooling passages....... don't know what ya do to cure that if that happens.......

also, when flushing the pieces out. look at the water pocket cover seal. if it leaks, ya may be introduceing hot exhust gas and hot water back into the system at the water pocket cover. if the waterpocket cover leaks. repost as water pocket cover bolts usually snap off when ya look at them, let alone trying to turn them, either direction..... be very carefull with the waterpocket cover...... it most likely will come to bite ya if ya mess with it....... to reitterate. DON'T mess with the water pocket cover bolts unless ya got no choice, if ya do yer likely in for a real hard time......

the rerouteing of the manifold water feed that bondo talks about i think is to address an issue that L6's had when they were plowing hard and the ft. of the boat is high. leaveing the ft. of the manifold w/o water, then when it gets water it cracks the manifold in the ft. for the sudden change in temp. http://forums.iboats.com/showthread.php?t=230973

 

[starsnstripers]

Re: Over Heating

If your in salt water and you have a raw water system i'm not sure if you want a pump from advanced auto. I believe you need a marine water pump that has brass workings to prevent corrossion. Maybe someone else can elaborate on this for you also to be sure. ( dont rule out head gasket) may want a compression test. Good luck! From L6 owner!

 

[Haut Medoc]

Re: Over Heating

SS is correct, make sure you have a marine water pump or you will get about twenty minutes out of it.....​