350 Mag Exhaust manifolds getting hot

[saurd]

I have a 2006 350 mag with a bravo 3 out drive. The exhast manifilds are getting extremely hot, to hot to touch. This has no always been the case. Others including a reputible boat mechanic have told me this should not be the case. Any ideas on for the best way to check out and learn what is causing this rather then just replacing parts.

 

[ThomW]

I'd start by pulling the elbows and see if there are rust flakes or chunks blocking the water flow through manifolds.

 

[saurd]

It will be a week or so before I get my boat out of storage. I will check this. Assuming there is some blockage found, what does this indecate?

Any recommendations on the best place to purchase the manifolds?

 

[alldodge]

I have a 2006 350 mag with a bravo 3 out drive. The exhast manifilds are getting extremely hot, to hot to touch. This has no always been the case. Others including a reputible boat mechanic have told me this should not be the case. Any ideas on for the best way to check out and learn what is causing this rather then just replacing parts.

When was the last time the impeller was replaced and the pump housing inspected?
Are you in salt or fresh water?

 

[saurd]

Impeller was replaced last year. The engine does not overheat. the boat is fresh water only.

 

[Scott Danforth]

have you checked for bravoitis?

 

[alldodge]

Impeller was replaced last year. The engine does not overheat. the boat is fresh water only.

I have a 24 year old fresh water boat and the manifolds are still in good shape. Replaced 20 year old fresh water manifolds off my cruiser during repower and there still setting in the shop and look good. So your 12 year old mans should be fine unless something extreme has happened to them.

Your mans will get hot, but not so hot that if you touch them you will be instantly burned. The port side is normally a bit cooler then the starboard because of how water flows the path of least resistance.

The 2006 motor (need serial number) will use the Gen 7 sea water pump. These pumps have a wear plate which needs to be checked. These pumps have also been known to loose suction after pulling boat out if its a bit worn

Do you have the 1,3 or 7 point drain system?
So how hot is it getting?
Have you used a IR temp gun?

 

[saurd]

I understand they will get hot, however these are hotter then I have noticed before, been boating for about 30 years.

Not sure what generation this is. The serial number of the motor is OW348398. I believe the it to be the standard cooling for this engine based onthe drawings I seen online. It is getting to hot for the touch, I have shot it with an IR temp gun but dont' recall the reading, it was last fall, the boat is not out of storage yet, in a bout a week or so.

Don't think it is bavoitis, the lower unit was off this fall to grease the spline and the mechanic doing the winterization did not say anything, and I think he would have knowing of this issue. If this were the case wouldn't the engine be overheating as well.

The recommendation I am getting from the mechanic is to replace the manifolds, but prior to going that direction I am wanting to assure this is the issue, both for cost and time reasons.

Once out of storage what are the checks to be done to help tell the root issue.

thanks for all the help.

 

[alldodge]

The S/N helps
With open cooling you can have either 3 or 7 point drain system.

The 7 point system s below uses check balls in the thermostat housing which go to the risers. These check balls slightly restrict the water flow to keep the manifolds full. If they get weak, then more water goes out the risers and less out the mans, causing the mans to get hotter.



The single and 3 point use item 20 (Tee) and the water distribution housing to restrict water flow to the risers. There have been many issues concerning water flow and winterization over the years



When you get the boat do some IR readings and we can figure out a path forward. Need to find out what the temps are and where it starts to get hotter

 

[QBhoy]

What was done to the engine recently ? Perhaps during winterising ? Thermostat taken out or anything ?
are they that hot you can’t touch them for more than a few seconds ?
ive noticed that the new dry joint riser system feels hotter than the old type, but not too hot that I’d be worried.
Maybe buy a heat gun ?

 

[saurd]

Thank you for the drawings. I see from this more then likely it is the single and 3 point. Hopefully in the next week to week and a half I will have the boat out of storage and be able to do this checking.

Were should I take the temp readings once it gets warmed up.

 

[alldodge]

Were should I take the temp readings once it gets warmed up.

Start at the exhaust and work backwards (Risers, mans, hoses). Thermostat should be 140 degrees, mans and risers should be less

 

[saurd]

Thanks for the info again. that is were I will start once I get the boat out for the season. I think the thermosat currently in the boat is 170 degree thermostat, should it be a 140 degree thermostat?

 

[alldodge]

Yes should be 140, the 170 is for closed cooling. Closed cooling has a heat exchanger mounted on the motor (round long metal thing).

BTW here is your motor

http://www.mercruiserparts.com/350-mag-mpi-alpha-bravo-0w310000-thru

 

[saurd]

Thanks again. Will continue once I can test the boat.

Have a great holiday.

 

[saurd]

Was finally able to get at working on the boat, April snow and other life stuff in the way. Ran it in the drive way with the muffs yesterday. After about 10 minutes running the temps of my lower manifold was already at 175 degrees on both sides with the whole manifold coming to the higher temp. the temp readings at the thermostat housing was 175, the in take was 145. Before it got hot I had verified flow by removing the hoses to the exhaust manifold while the engine was running, I don't believe there is any blockage there. Then I decided to replace the impeller as it had been at least 2 years. The impeller looked good. I pulled one of the risers and there is a lining of corrosion visible at the inlets which I know can inhibit the heat transfer.

Please let me know your thoughts. Not sure what else could be cause the heat build up.

Thanks

 

[alldodge]

lining of corrosion visible at the inlets

Don't know how much there is, but your correct this can cause an issue. Removing the hose going to the manifold shows that water is coming out of the hose, but doesn't show if its being restricted when the hose is reconnected.

Everything is at 175 except the intake. Even if your thermostat was 170 this wouldn't mean the manifolds are up there as well unless there is not enough flow, or there is something like a head gasket issue.

Bravoits would be my next check. Need to remove the intake hose from the transom assembly, then remove the fitting that connects the hose to it. Once fitting is off, if there is Bravoits then it will be seen.