4.3 over heating at low rpm Help

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Griff Thomasson

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I have a 1993 4.3xl Mercruiser in a 2050 Chaprell , boat runs great how ever pulling throttle back in no wake zones over heating alarm goes off . Open her up and she cools down ...
I replaced 160 deg thermostat last season to a 140 and no difference ... drilled 3 -1/4 inch holes in thermostat
I have cooling system torn down completely , New impeller in out drive ( new out drive ) While out drive was off boat I back washed hose from out drive checking for clogs in power steering cooler ...
Risers are fine ---one manifold is new , other found a hair line crack outside .. replacing that one ...
I pulled water pump off and will replace it with a Mercruiser pump... with pump off using a hose I flushed each side of the block with drain plugs remover , using a pick in circles and got out rust scale maybe 1-2 table spoons from each side , cant fill each side up with water now ...
I suspect this may have been part of the problem !!!!
I found a quarter sized piece of scale on hose going from pump thermostat housing ?
May have been part of the problem ???
Any suggestion on cleaning the block out ???
I am 72 owned boats all my life
OH I checked to make sure no spark plug wires were in correct order they are correct
Boat in fresh water as long as I have had it !
 
alldodge

alldodge

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Being a 1993 the 4.3LX can have either a 4 port or 6 port thermostat housing. Which do you have?

Serial numbers are great
 
Scott06

Scott06

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Griff Thomasson said:
I have a 1993 4.3xl Mercruiser in a 2050 Chaprell , boat runs great how ever pulling throttle back in no wake zones over heating alarm goes off . Open her up and she cools down ...
I replaced 160 deg thermostat last season to a 140 and no difference ... drilled 3 -1/4 inch holes in thermostat
I have cooling system torn down completely , New impeller in out drive ( new out drive ) While out drive was off boat I back washed hose from out drive checking for clogs in power steering cooler ...
Risers are fine ---one manifold is new , other found a hair line crack outside .. replacing that one ...
I pulled water pump off and will replace it with a Mercruiser pump... with pump off using a hose I flushed each side of the block with drain plugs remover , using a pick in circles and got out rust scale maybe 1-2 table spoons from each side , cant fill each side up with water now ...
I suspect this may have been part of the problem !!!!
I found a quarter sized piece of scale on hose going from pump thermostat housing ?
May have been part of the problem ???
Any suggestion on cleaning the block out ???
I am 72 owned boats all my life
OH I checked to make sure no spark plug wires were in correct order they are correct
Boat in fresh water as long as I have had it !
Click to expand...
Did you verify the engine temp with a IR thermometer to see if the alarm switch is accurate and should be going off ? checked the ignition timing isn't retarded? Did you test it after the circ pump was replaced?
 
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Griff Thomasson

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Scott06 said:
Did you verify the engine temp with a IR thermometer to see if the alarm switch is accurate and should be going off ? checked the ignition timing isn't retarded? Did you test it after the circ pump was replaced?
Click to expand...
Have not tested yet with new cir pump its coming Wednesday ---I just bought an IR Thermometer ----Ill go get serial numbers .
I have a 4 port thermostate housing meaning 4 hoses coming off it
 
alldodge

alldodge

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Thanks
Get a piece of clear hose from HW store. Remove the hose going into the thermostat housing coming from the power steering cooler. Place it inline with other hose.

Run the boat in the water and see if there are any bubbles. My guess is there is a air leak

If no air leak, remove same hose and place in 5 gal bucket and at idle how fast is it filled
 
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Griff Thomasson

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alldodge said:
Thanks
Get a piece of clear hose from HW store. Remove the hose going into the thermostat housing coming from the power steering cooler. Place it inline with other hose.

Run the boat in the water and see if there are any bubbles. My guess is there is a air leak

If no air leak, remove same hose and place in 5 gal bucket and at idle how fast is it filled
Click to expand...
Thanks Dodge
 
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QBhoy

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Hi. If she has had an overheating issue previously…you might find that one or both of the exhaust flappers have melted and found themselves down the exhaust somewhere…causing a blockage
 
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Griff Thomasson

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I am an old dumb ass ! It is a 6 hose thermostat housing . Yes the springs were lose on the back flow balls and shaft was bent , letting water flow to exhaust instead of engine ... May have been part of the problem !
I pulled thermostat and check it today open as it should .New water pump came today I put that back on . Cleaned up mating surfaces on exhaust manifolds ..
I put new exhaust flappers last fall
One manifold was cracked ordered a new one other side it only 2 years old ...
 
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Griff Thomasson

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It was hot here today . I got up early and put engine back together .. This is what I have done trying to correct an over heating problem at low rpm
New impeller in outdrive ( new outdrive )
Pulled old water pump replaced with Quicksilver water pump
Pulled 145 deg thermostat checked in water opened as it should also drilled 3 1/4 inch holes in thermostat
Pulled exhaust manifolds off and risers risers were fine , one manifold was cracked replaced it with new manifold ...other manifold 2 years old
New gaskets
When I had water pump off I pulled drain plugs and flushed block out ..
I finished putting everything back together this morning and am heading to the lake in the morning to test it out !
Fingers crossed
I have the 6 port thermostat housing and the spring loaded balls , the shaft was bent and spring weak --- I stretched springs out and straightened shaft , those balls pulled up tight force water through enging at low rpm and open up wide open ..
 
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Griff Thomasson

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Up date on todays test ... Took her to the lake this morning . Fired her up and let her idle at dock , opened engine cover and had water coming from water pump . Dumb ass me forget to torque that down . Ran back to house and got tools . Torqued down the water pump bolts .. stopped the leak
How ever idoling at dock at first she was at 145-150 ----then shot up to 200..alarm never went off ... I shut it down ....
I noticed what looked like and exhaust leak just behind fuel pump ?? Could not tell if that was coming from exhaust manifold or head ??
I took her out and opened her up and ran at 3200 rpm temp settled down at 145-`150 ran a good 20 miles ...
Headed into a cove for lunch -----gotIR temp gauge out and put batteries in it and checked around engine .. got readings of 175 -205 was highest I found Still have a small water leak from thermostat housing ( have to torque that down )
I need to retorque exhaust manifolds ... after that run
Coming back to dock I throttled back and eased her in and temp stayed at 150 or less ???
I may have a head gasket leak exhaust gases going into water jacket ????
 
alldodge

alldodge

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Gauge is staying 145-150 right?

Where did you get readings of 175-205?
 
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Griff Thomasson

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alldodge said:
Where? Thermostat housing or other
Click to expand...
I have never used a IR thermometer , I shot top of riser and around on exhaust manifolds . It would make sense to check thermostat housing , it was heavily coated with condensation . where to check on engine ? Where do you check ?
IR thermometer is a cool tool to have !
 
alldodge

alldodge

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The exhaust would read higher and that can be ok.

To find out if your motor IS actually overheating is to measure the thermostat housing and compare the IR reading with the boat gauge. If they read close to the saame then there is a overheat, if not then might be a gauge issue
 
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Griff Thomasson

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alldodge said:
The exhaust would read higher and that can be ok.

To find out if your motor IS actually overheating is to measure the thermostat housing and compare the IR reading with the boat gauge. If they read close to the saame then there is a overheat, if not then might be a gauge issue
Click to expand...
thanks Dodge Ill check that out
 
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