2400scr overheating at low throttle

[viper12161]

Hey everyone. So quick review of my boating woes this summer Just had my marina put a brand new transom assembly and outdrive on my boat after I hit a rock. Got a quicksilver transom assembly and an SEI drive that I had my marina put in. They just finished it on Friday. When they took it for a sea trial, they said it was running good but it got hot just as they were getting to my slip. I figured hmmm, it was sitting for a bit, maybe the Thermostat was stuck. So I replaced that Friday night. I put in a 160 t-stat per the spec. Ran it at the dock for about 45 minutes and she stayed right at 175 where it always runs. Figured sweet, good to go. Took it out this morning for the drive break in. Was cruising around the bay for about an hour and it was running great. Went to come back in and about 5 minutes into the no wake zone, alarm started going off and it was running at about 200 degrees. Once I got it back at the dock, checked the elbows and tstat assembly with my temp gun and all three were just about 200 degrees. I know the first thing out of the marina's mouth is going to be elbows and manifolds, however, when I had the tstat assemble off and the hoses off I was able to put water through the hoses to the elbows without issue and had good flow, so I don't think it's that. I'm thinking they pinched a line somewhere when they were putting everything back together and now it has low flow. The drive came with the upper and lower separated, so maybe they didn't put it together right. Anyone have any thoughts on what this could possibly be. I already emailed them to let them know there is still an issue here and would like to have some knowledge in my back pocket in case they try to BS me. This thing ran like a top before I hit the rock. Thanks!!

[mmwjr]

My first thought is the hose from the transom to thermostat housing is pinched by the rear engine mount.

[viper12161]

Thanks Mike. Kinda my thought as well. I don't think they took the whole engine out to replace the transom, I think they just supported and tilted it, so thinking when they dropped it back down maybe it caught that hose.

[mmwjr]

Originally Posted by viper12161

Thanks Mike. Kinda my thought as well. I don't think they took the whole engine out to replace the transom, I think they just supported and tilted it, so thinking when they dropped it back down maybe it caught that hose.

Pretty easy to verify, get your head back there and find the hoseto see if it’s free or not.

[viper12161]

I just paid them a ton of money to do this....and I'm fluffy lol. I'm leaving it up to them to check.

[mmwjr]

I’ll be interested in hearing what the issue is.

[viper12161]

Will definitely report back on findings

[viper12161]

So as I suspected. Marina is saying it's the manifolds and elbows. He said the tech temped them out and one is running 35 degree's hotter than the other one. Not sure if I am buying this or not...but curious what others with a bit more experience think. Does this seem plausible? I honestly have NO idea when these were changed if ever. I checked the service records I have from the previous owner (he was the second owner) and nothing in there for it. He's quoting it at 10 hours to do as a worst case in case bolts break, but said probably going to be less than that. Now debating if something I want to tackle myself....elbows look pretty straight forward, but not sure on the manifold.

[mmwjr]

Replacing the exhaust is not to difficult. One trick is to use a piece of all-thread on the 2 outer location to all you to install the gasket and manifold then the 2 center bolts. Finally remove the 2 all-threads and install the bolts. Then torque them all up. It’s not uncommon to see a difference between both sides I would get an IR temp sensor and take reading of the thermostat housing, exhaust manifolds and risers. It’s just strange for this to start after this incident unless something got sucked up into the cooling system.

[viper12161]

Great tip!! I found a water flow test in my Seloc manual, so I am going to head down Friday night and do that just to confirm it isn't in fact a flow issue. If it isn't then I will tackle the Manifolds and pray for the bolts to play nice. At this rate, I will prob just call it a lost season, use it as a floating hotel the next couple of months, and do it in the fall/spring.

[Phillbo]

I skimmed the thread but has anyone suggested a new impellor?

[viper12161]

Brand new drive which came with a new impeller. I mean, I'm assuming it's good. But who knows.

[mmwjr]

Under Documents you can get the Mercursier manual #24 for your engine which is better than the aftermarket ones. I’ve never had the GM small block exhaust bolts break but have on the big blocks as they are under the manifolds and tend to rust. Worst case it’s a day job less if you mechanical. Run the engine to heat them up which will help break them free. Then crack each one loose followed by removal. These are iron parts so they have some weight to them.

[mmwjr]

Originally Posted by viper12161

Brand new drive which came with a new impeller. I mean, I'm assuming it's good. But who knows.

This is why I asked to IR temps

[viper12161]

I temped it out when I came back in and the alarm was going off. Both elbows, manifolds and tstat were at 200 degrees.

[viper12161]

So I went down today and pulled the hose from the drive off at the thermostat housing to check the flow. According to the manual, with the hose off and running at idle, there should be a 2-4" column of water coming out. It barely comes out of the hose. I took a video of it but it won't let me attach. So here's a screen shot of how high the water goes. Does not seem like there's enough damn flow.

[mmwjr]

In the Mercruiser manual the flow test is in gallon per time and is a better test but it’s like you know where the issue is. This could still be a pinched hose.

[viper12161]

Thanks Mike. Yeah, I had seen the official merc test. My drive should be pushing out 3.6 QT's in 15 seconds at 1000 rpm. So just under a gallon. It calls for removing the hose at the gimble housing water tube and replacing it with a similar sized hose 3' longer. I just don't think I can get back there to take that hose off. It also calls for a shop tach and specifically says not to use the dash tach. But seeing the flow I had just having the hose off like I did, I don't see it pushing out those numbers. I might try and see if I can do this just using the existing hose, but not sure how accurate it will be. They are pretty specific on everything needing to be perfect to validate test. From time to RPM's. My test was probably at about 800-900 rpm, so pretty damn close to the required number I would think and I truely don't see that pushing 4 gallons per minute. Wish I could attach the damn video here lol

[viper12161]

I learned how to upload to Youtube Here' s the link to the video. Hopefully it works.
https://youtu.be/dssRb4ivTTA

[mmwjr]

I’ve only done the test using 5he existing hose and when things are working properly achieved results that satisfied the recommended flow. You definitely have a flow issue. Things to check, pinched hose by engine mount, bad seal on the outer transom, water pump output to upper water tube connection, water pump.