Mercruiser 4.3 One-Piece Exhaust Manifold Hot

[jtw]

I have a '98 Mercruiser 4.3LH/Alpha 1. It is used in mildly brackish water, and flushed every time it is used, since it has an open seawater cooling system. It has the one-piece exhaust manifolds.

The other day, I was doing some work and noticed that the stbd manifold was so hot that I couldn't keep my hand on it. The port manifold was just warm. It may have been this way for a long time. I really never noticed. The boat hasn't had any overheating issues.

I'm guessing that I have some blockage within the manifold. I know it is clear to the inlet. Is there a way to check for and clear blockage without taking that 50 lb hunk of metal out? Does anybody have a drawing of what the internal piping of this manifold looks like?

Since these are original, I know folks are going to tell me to fork over the $$$ for new manifolds. Does anyone want to give me a loan? Why were the one piece manifolds discontinued?

Thanks.

 

[cooter2506]

Re: Mercruiser 4.3 One-Piece Exhaust Manifold Hot

Do you have a IR temp gun? If not get a cheap one and check your temps. If you are not having an overheating problem you probably dont have a problem. One riser is always hotter than the other. Ususally about a 15-20 degree difference. One could be 120 and other could be 140 cant hold hand on that very long. Shoot the temps of both risers and also at the temp guage sending unit just to verfy your engine temp.

 

[180shabah]

Re: Mercruiser 4.3 One-Piece Exhaust Manifold Hot

" I was doing some work..." - I take this to mean, idleing on the hose....

If so, neither manifold should be hot enough to prevent holding it. You have 11 year old manifolds that have seen salt (only a little at a time, but it has been there). Unless you have had an impeller destroyed and send chunks through the system, your blockage is most likely rust chunks from your deteriorating manifolds.

Why were they discontinued? No way to inspect them annually like you can with a 2 piece setup. Most people didn't know there was a problem until they hydrolocked an engine.

Yes you can rod them out - if you get rubber chunks, reuse the manifolds. If you get rust, be thankful that you caught the warning signs and replace them. I would suggest going to the 2 piece design.

 

[Bondo]

Re: Mercruiser 4.3 One-Piece Exhaust Manifold Hot

Why were the one piece manifolds discontinued?

Ayuh,.... Because they were Junk the day they were New....

I'm seeing lot's,+ Lot's of Issues with those things,... Even up here in the Sweetwater...

Buy an Up-graded set of 2-pc. manifolds Now,...
Or a complete replacement Motor sometime in the probably Near Future...

 

[jtw]

Re: Mercruiser 4.3 One-Piece Exhaust Manifold Hot

Thanks for replies. They bring up 3 more questions.

First, I was at idle on a hose. Why would one manifold always be hotter than the other when everything is working right? The routing from the thermostat to the exhaust is perfectly symmetrical. I've seen folks on this forum have that happen if the boat isn't level while on the hose. But a temperature difference is normal? When the thermostat pops open, does it **** over to one side or the other a little?

Second, when you say that I can rod it out, I'm guessing that I'd have to remove that big honkin' manifold. I still haven't been able to find a drawing of the internal channels.

Third, when I do convert from one piece manifolds to 2 piece, are there any that give a performance increase?

I really wanted to get this boat out on the water to determine if I have any other major issues, but it looks to risky.

 

[Bondo]

Re: Mercruiser 4.3 One-Piece Exhaust Manifold Hot

Ayuh,...

First,... Water flows the path of least resistence,+ it'll Never be Exactly the Same....

Second,... I Wouldn't,.... I'd Scrap 'em before they cost you a Motor...

Third,... I haven't seen any Headers for the V6s,...
The 1s for SBCs,+ BBCs run well into the Thou$and$ to buy...

At the very least,... Find a Used freshwater set from ebay or craigslist...

 

[Jet Lag 176flyer]

Re: Mercruiser 4.3 One-Piece Exhaust Manifold Hot

check your messages jtw

 

[jtw]

Re: Mercruiser 4.3 One-Piece Exhaust Manifold Hot

I still haven't found a diagram of what the internals of the one-piece manifold. Is it jacketed by the water? Does the one hot manifold mean that I have corrosion inside the channels for the water that restricts water flow, and thus makes it hotter? Or does the one hot manifold mean that there is a leak between the water jacket and the hot exhaust gas (if there is a jacket)?

 

[180shabah]

Re: Mercruiser 4.3 One-Piece Exhaust Manifold Hot

Yes, they are water jacketed manifolds.

The rust that clogs them, used to BE them. When they perferate internally, you will be replacing your engine, after the water that was supposed to be IN the manifold drains back into your engine via an open exhaust valve.

 

[nofuss]

Re: Mercruiser 4.3 One-Piece Exhaust Manifold Hot

Ok sorry for posting this here but i think something is wrong and i am unable to post new topics.
I just removed a pair of these 1 piece manifolds, but wanted to know if it is likely that i may have created a bigger problem.
I went out with my boat and it worked well, no problems. on trying to return my port engine refused to start.
i came home on starboard engine flushed it and paid attention to port engine.
trouble shooting showed water on plugs. suspect manifolds. removed them etc.
decide to try to start starboard engine just to keep it active. plan is to change all 4 manifolds. initial try engine seems locked, or battery very dead, removed #1 and #2 plugs they looked ok replaced in engine. second try engine sounded like it turned over with a bit of mechanical noise. not very loud. stopped and removed remaining plugs, #5 plug water wet and dirty. turned over engine using remote started with ignition off and all plugs out. Water seen to come out of #5 cylinder, but small amount, engine turning over freely. removed manifold on that side foamed up cylinder and exhaust port with power foam, left for about 10 mins, While removed other manifold. and then cranked the engine to get foam out. then lubricated exhaust ports, and all cylinders with transmission oil, through plug hole. Cranked engine several times to ensure properly lubricated. all holes spitting out transmission fluid.
is there a real possibility that i may have done major damage to the engine in the initial crank.
sounds unlikely to me that the starter, would be strong enough to do mechanical damage, but i know there is a wealth of experience here on this forum. and although i am a pretty competent mechanic, i am not very familiar with V configuration inboard engines, or for that matter inboard gas engines on the whole.
I am praying that this was not likely, as getting manifolds to trinidad is enough stress much more bigger parts.

hoping for some replies
thanks
Pernell
also if anyone could give me an idea y I am not seeing the post new topic button i would appreciate it

 

[Bondo]

Re: Mercruiser 4.3 One-Piece Exhaust Manifold Hot

Ayuh,... At this point ANYTHING is Possible....
Being in Salt, get that motor Running, atleast for a minute to purge any remaining salt out of it...
Hopefully, nothing is Bent, but get it Started...
Then replace All the manifolds with 2 piece units..