Overheating Troubleshoot - 4.3L Mercruiser MPI

Mini Yacht

New Member
May 17, 2018
4
Connecticut, USA
Boat Info
2002 Sea Ray 185 Sport - Bowrider
Engines
4.3l Mercruiser 220hp - #0M300066
Transom - #0M290514
Alpha Gen II Drive - #0M406192
Hey Guys,

I recently purchased a 2002 Sea Ray 185 Sport two months ago and I'm trying to troubleshoot an overheating problem. I purchased the boat without knowing ANY maintenance history as the boat was owned by a Cobalt dealer as a trade-in.

The engine is a 4.3L Mercuiser MPI (Serial #0M300066) with an Alpha 1 (Gen II) Drive (Serial #0M290514) and they're both original to the boat as far as I'm aware.

I replaced the 160 degree thermostat with a new one this past weekend, and the boat wants to overheat at idle during the sea trial in 50 degree water. At idle, the boat approaches 220 sitting at the dock (before I turned it off and let it cool). However, when we took it out and opened the throttle up a bit, the temp got a little cooler. 190 degrees was the lowest temperature appearing at full throttle - about 42mph or so. The boat had no problem staying at 200 degrees under power, but approaches 220 at idle when sitting at the dock for 3-5 minutes.

What do you you guys suspect? I'm thinking the lower unit's water pump may be to blame. If that's not the culprit, should I replace the circulating pump on the motor? And then do risers and manifolds? The boat was used in brackish waters for several years and then sat for about a year before I bought it. Any help is appreciated!

I'm currently ordering the water pump as we speak, but I'm hoping that a DIY tutorial can also be provided if possible. I've never removed the lower unit from a vessel, and I'm a little bit apprehensive about the process after reading about it in my Mercruiser repair manuals.

Thank you guys for your time, please respond back with any questions if I wasn't specific enough. I'm hoping to get on the water as soon as possible!

-Kevin
 
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Can you provide any water pressure readings?
I don’t think a 2002 model year has that feature.

If not, what about pulling off the raw water inlet hose and seeing how much water the pump is actually supplying at idle.

You can remove the plugs from the underside of the exhaust manifold and see if they are packed with rust and debris.
 
Can you provide any water pressure readings?
I don’t think a 2002 model year has that feature.

If not, what about pulling off the raw water inlet hose and seeing how much water the pump is actually supplying at idle.

You can remove the plugs from the underside of the exhaust manifold and see if they are packed with rust and debris.

Unfortunately there are no water pressure readings. I figured that while I'm waiting for the lower unit's water pump to arrive, I'll inspect the hoses for debris. When pulling off the raw water inlet hose, should I run the motor and check flow? Or should I see how much water is being supplied via pressure with the motor off? Or both?

Thanks for the help guys. Other than this temperature issue, the engine hasn't skipped a beat and runs absolutely great. I'm going to check the engine oil again as well, but it looked clean after the original sea trial two months ago.
 
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You need to have the engine running to see any flow from the hose.
 
I think I would just start with the water pump, you don't know know when it was last changed, the service interval is every 2-3yrs on a Alpha Gen II. It's cheap and easy to replace, then you are starting from a known good point. You could have other issues with clogged risers etc, but if the water pump isn't working right, it's just not going to cool properly.

Circulating pump on motor lasts a long time, telltale sign of a failure is a leak from the weep hole on the front of the pump.
 
dont waste a bunch of money replacing parts...

when i got mine.. slowly overheated

after both pumps replaced, thermohousing, etc.. 3rd time removing all hoses found piece of old impeller... pump had a new one in it but prevowner servicing didnt go through system... runs great now

check impeller 1st
start at hose from pump, look through each section... i bet you find a broken piece blockage
 
Did you ever find out what was causing the issue?
 
Unfortunately I’ve been unable to solve the issue. So far, i’ve replace the theromastat, manifolds/risers, raw water pump and circulating pump. The only thing that made a difference was the circulating pump- it now runs at 205 instead of constistently climbing to 220.

I’ve resorted to handing my vessel off to a very notable shop in my state. (ocean performance of Old Saybrook, CT). I dropped it off this weekend and they’ll be looking at it on Tuesday. I’ll definitely report back.
 
I am haveing a similar problem. Please keep us updated and good luck.
 
On the alpha I gen II drives lower unit there is two cavities, one is where the water pump pulls the fresh water in from and the other is where the exhaust gas and hot water exits from. There is a 1/8" thick partition that separates them and it gets corroded away in time and will start pulling exhaust gas and hot water back into the motor. When you do the lower water pump you'll see what I'm talking about. Easy fix just rebuild the partition with JB weld for aluminium and should help with your problem. Happened on mine
 
On the alpha I gen II drives lower unit there is two cavities, one is where the water pump pulls the fresh water in from and the other is where the exhaust gas and hot water exits from. There is a 1/8" thick partition that separates them and it gets corroded away in time and will start pulling exhaust gas and hot water back into the motor. When you do the lower water pump you'll see what I'm talking about. Easy fix just rebuild the partition with JB weld for aluminium and should help with your problem. Happened on mine
This is a gen 1
 
I think they're both the same, pull the pump housing off and the two cavities are there, no one notices them cause they never pull the housing off the lower unit, mine had a lot of corrosion and my mechanic told me about it or I would not have noticed it as the partition on mine was 3/4 of the way gone and it did help cool the engine down as the water pump impellor did look good.
 
Thanks. I will be sure to look it over later.
 

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