Merc 4.3LX Overheating

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wishihad

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I just bought a 92 Maxum 2100 SC with a Merc 4.3LX. The boat ran great for about 30 minutes thru a long no wake zone, temp indicated around 215F. After clearing the no wake we ran 3/4 to full throttle, 46 mph at 5k rpm, for about 5minutes then started to overheat and showed 250F+. Immediately, after I shut it down I put my hand on the exhaust heat riser and it was cool, then after sitting for 10 minutes it was very hot. We restarted the engine and the riser cooled down very quickly but the temp stayed around 220F, we were able to run at a low power setting back to the ramp with out further incident. I HOPE it is the thermostat. It didn't come with the manuals, so I ordered the engine manual. The engine seems strong, starts easily, and idles well. Any thoughts?
 
Bondo

Bondo

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Re: Merc 4.3LX Overheating

1) Inspect, +/or change the Raw Waterpump Impeller.....

2) You No Doubt Fired the Exhaust Flapper Valves,.... Replace them....

3) I doubt the Issue is the T-Stat, but I'd change it anyways.....

The boat ran great for about 30 minutes thru a long no wake zone, temp indicated around 215F.
Click to expand...

It was Over-heating Then,....... Why didn't you return to the dock at that time,..??..??......

A Raw water cooled motor runs at 140*......
A Closed-Cooling System motor runs at 180*.......

At the rate you're going,..... Your motor is going to be Junk,... by June........
For the Hour,Plus that you've run this motor, in an Over-Heated condition,......
You've probably Used Up about 1/2 it's expected life expectancy.......
 
Don S

Don S

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Re: Merc 4.3LX Overheating

It may be the thermostat, could also be a very loose alternator belt (Usually from rusty pulleys eating the belt). It also runs the engine circualtion pump.
While it may not be your problem, when was the last time the impeller was replaced?
 
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wishihad

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Re: Merc 4.3LX Overheating

Bond-o said:
1
It was Over-heating Then,....... Why didn't you return to the dock at that time,..??..??......
quote]

We were not aware of the correct operating temp range for a raw water cooled IO. Plus I've seen automovive engines run @ 200F with no problem. But it seemed high so we pulled the hatch and felt the risers and the manifold which were cool to the touch so we (ass)umed the gauge was inaccurate. It still may be.

Not sure we took 1/2 the life of the engine but we didn't do it any favors for sure! What does the fact that the risers were apparently getting water but not the block imply?
Click to expand...
 
Haut Medoc

Haut Medoc

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Re: Merc 4.3LX Overheating

You haven't said if this is a closed system of a raw water system.......
Change the impeller, so you know its condition.....
Replace the thermostat......
Make sure that the engine circulating oumo is operating properly.....
Verify engine temp./gauge......;)
 
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wishihad

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Re: Merc 4.3LX Overheating

Raw water cooled.
Is there an impeller in the outdrive and a water pump on the engine?
tnks
 
Haut Medoc

Haut Medoc

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Re: Merc 4.3LX Overheating

Yes....There are two -
You most likely have an Alpha 1 generation 2 drive....
You should post your engine serial # to be sure......
That manual might be available online....
But I don't have a link....
Someone else might......:)
 
Bondo

Bondo

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Re: Merc 4.3LX Overheating

If your boat has the Alpha drive,... It's the Impeller in the Outdrive that needs attention.....

If it's Bravo drive equipped,.. It'll be mounted on the motor,+ turned by a Belt......It'll still be a Raw water pump, Not the 1 Bolted to the face of the Block....

The engines Recirculating waterpump, Rarely is the Issue.......
 
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wishihad

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Re: Merc 4.3LX Overheating

Serial # OD721636, 1992 Merc 4.3LX

Ordered a manual should be here in a day or two.
Thanks for everones help!

Can someone discribe the water flow path (typical 4 a I/O raw water). Thanks.
 
Bondo

Bondo

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Re: Merc 4.3LX Overheating

You still haven't said What Drive is behind it...........

Yes,....... It Does Matter..............

I'm going to Guess it's an Alpha,.....

Water is picked up,+ pumped from the Outdrive thru a hose to the T-Stat housing, there it splits to the Recirculating Pump to fill the Block,+ Excess is pushed thru the Manifolds,+ Out the Risers......
'Course, when the T-Stat Opens,..... The Hot Water is replaced with Cold,+ the Hot exits thru the Manifolds......


Btw,....... If by chance you've got a Bravo,........That's All Wrong........
 
W

wishihad

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Re: Merc 4.3LX Overheating

Bond-o said:
..Guess it's an Alpha,.....Water is picked up,+ pumped from the Outdrive thru a hose to the T-Stat housing, there it splits to the Recirculating Pump to fill the Block,+ Excess is pushed thru the Manifolds,+ Out the Risers......'Course, when the T-Stat Opens,..... The Hot Water is replaced with Cold,+ the Hot exits thru the Manifolds.......
Click to expand...

So if the T-Stat never opened and the impeller in Outdrive was working cold water would flow thru the risers but not the block correct?
 
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