Mercruiser 4.3

[DavidP]

Hi

I have a Mercruiser 4.3L ,V6 with an Alpha one leg. 1989
Problem,,,,
On tickover at around 750 rpm the engine starts to overheat , move the throttle to around 1100 rpm and above and the temp drops and remains constant and safe, any ideas on the problem and how to fix it .

Cheers ,
Dave.

 

[Guest]

Have you checked your impeller?

 

[tr7v8]

As Grumpy1 says it could be the impeller or as it's raw water cooled it could be clagged up waterways. Is it running OK otherwise? No excessive oil or water consumption? What state are the rubber hoses in, it could be a partially collapsed one.
Unfortunately on a Merc checking/chamging the impeller is a boat out of water/ partially dismantle the leg job, BUM!

Jim
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[DavidP]

Hi Grumpy

Sort of guessed it may be the impeller , but have no idea where it is

Dave.

 

[Guest]

It's in your leg. I bought the volvo 4.3 for that very reason, as theirs is easily accessable at the front of the engine. I am no expert and don't have a boat yet, but have found this problem during research. I get mine on 22/3 Good luck anyway.

 

[DavidP]

Grumpy 1,,,Tr7v8

Cheers,

Thanks to the both of you , i have lived with it for the last 6 months , but will have a look at it now i know where to look, when it comes out in the spring .

Thanks again
Dave.

 

[Guest]

Re: Grumpy 1,,,Tr7v8

My new impeller I bought as a spare was £25, got it at LBS. I would get some advice as it is not worth damaging the engine for £25 part.

 

[BarryH]

Re: Grumpy 1,,,Tr7v8

If its an alpha 1, you'll have to drain the outdrive oil before you drop the gearcase. Is it a gen 2 drive?

 

[David2452]

Symptoms certainly indicate worn impellor and or wear plate(s), 1989 puts you on the cusp of the change to gen II drive which has a higher capacity pump so make sure you get the right kit. Do not replace only the impellor get a full kit. No need to pay Mercruiser prices as both kits are available as pattern parts.

David

 

[ballena]

I had exactly the same problem with my Volvo 5.0.

I changed the impeller first and it did nothing.

The problem was the thermostat had rusted shut. The volume of flow at low revs is insufficient to cool the engine, the risers and exhausts will stay cool because of thye bypass, but the block will get hot.

As the revs increase the flow volume increases and the engine gets some cooling effect.

Be sure to grease the new thermostat when fitting with a small amount of thick grease, this will help with corrosion protection.

The thermostat housing is mounted on the top of the engine just in fromt of the carb.


Good luck

Send me a PM if you need any other help.

V8's rule!

 

[spannerman]

Before you take the boat on land, check the output from the water pump, just take off one of the hoses that goes to the riser or manifold depending on which type of thermostat housing you have, and run the engine briefly, making sure you aim the hose into a bucket. You should have a decent flow, if its a dribble at idle then you know its the impellor or a collapsed hose between the leg and transom, if its good then check that the thermostat isn't stuck closed.