Mercruiser MCM 181 3.0 Overheating issue

[MidwestFloater]

Hi all,

I have a 2000 Sea Ray Bowrider 180 with Mercuriser MCM 3.0L a / L605518 serial variety.

I was having a number of issues with idling and acceleration recently so ended up rebuilding the carb. After that the fuel system issues seemed to be a lot better at idle and accelerating when not in gear (in the harbor).

However, after taking it out for the first time post rebuild we started to experience pretty serious overheating issues. We appeared to be getting no flow through the cooling system when in gear. We were stranded out in the middle of the lake with high temp but were able to get it home by disconnecting drain on the engine block cooling line and letting water flow to the bilge. So we were getting water through the block and keeping temperature down.

This morning we replaced the thermostat and that didn't fix the problem. We are able to idle alright when not in gear, which took the temp to ~170F, but when placing it in gear pretty quickly start to overheat. We then tried a couple tests. We first disconnected the engine drain block to bilge as we had the prior day and put it in gear. Again, we had good flow and the temp remained low. Next we did the same test but with the exhaust manifold drain disconnected. Again, we maintained temperature and had pressure out of the exhaust manifold drain.

So it appears to possibly be a blockage coming off the exhaust manifold to the final exhaust. I don't get why there would be any difference in this if it were in gear versus not in gear. Any ideas on what it could be and what steps to take next (before maybe breaking off the elbow on the top of the exhaust manifold!)

Thanks!

 

[Bt Doctur]

Stop running it until you fix it. First is replacing the water pump in the outdrive..Verify good flow out the exaust , if marginal find out why. Opening up the drains does nothing but remove the flow from the exaust and the rubber components. No water out the exaust fries the water pump.

 

[MidwestFloater]

Ok, broke apart the lower unit and there were a lot of issues in the water pump. I should have realized this before I ever took the boat out since I found part of what I now know to be the water shutter in the exhaust bellows....

Anyways, I've attached pictures of the impeller and melted components from the area. Here's my current take on the wreckage:
- Impeller
- Water pump guide tube (white one)
- Water tube adaptor
- Water seal
- Upper exhaust water shutter

I'm planning to replace all those items, gaskets, etc.. I'm also planning to do the oil seal carrier while I'm in there. Are there other components I've missed that might melt given the broad system overheat? I don't think we've cracked a head gasket, but are there other engine aspects I should inspect as well?

Also, the mating surface where the water pump housing attaches is pretty worn and I'm worried about a gasket making a good seal (see attached). Should I try to apply a smaller layer of some type of epoxy or other material to that surface before reattaching things? I'm planning to paint it at the very least, but think smoothing it out would help. Thoughts on what material would work for that?

Thanks!!!

 

[Scott Danforth]

without water running, you burned all the rubber bits in the exhaust too.

get a complete new water pump assembly

 

[MidwestFloater]

Yeah, I have the quicksilver water pump assembly kit. I think between that and the water tube parts, that's pretty much everything except the housing. Think I'm missing other things?

 

[TunaFish389]

Edit.. Deleted, didn't read right.

 

[MidwestFloater]

Here's the list of specific plastic / rubber items I've ID'd so far. Any big missing ones jump out?

- Impeller
- Water pump guide tube (white one)
- Water tube adaptor tube
- Main water tube line
- Water seal (on shaft on top of housing)
- Upper exhaust water shutter
- Oil seal carrier

I've also got a new gasket for the exhaust manifold elbow in case I have to bust that loose. I'm probably missing some stuff yet though...

 

[achris]

Pull the elbow and check for condition of the water passages. Most likely it's beyond it's 'use by' date and is blocked up, and that's why you're not getting flow through....

Just looked at the photos. Your impeller is ok (not great) , indicating it was pumping water. The external parts are the worst I have seen for a long time, and that's because you discharged the cooling water into your bilge, and they got full uncooled exhaust gases...