Volvo 4.3/overheating/pulled thermostat - help!

harleyfool

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Jun 7, 2009
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2000 - Volvo 4.3 GL - SX-M drive

To summarize (1) After 2 1/2 cruise dragged boat home and tried to flush with muffs on. No water return. Checked impeller and found it was damaged. Replaced. Removed thermostat housing. No obvious impeller parts. Had a spare thermostat so replaced. Restarted boat and runs hot to 200+ degrees. Hose from thermostat housing to water pump is warm. Hoses to manifolds cold.

(2) Took hoses off sea pump and flushed both ways. Rechecked impeller = OK. Took thermostat housing off. Took out "new" thermostat and placed in hot water. It opened. Checked all ports = no debris. Removed all attached hoses and no debris. Took hoses of left and right manifolds. Repeatedly flushed manifolds = good return out the stern drive. Also let the manifold back drain. Removed the water pump. Spins freely. Unable to visualize fins. Flush the block thru the two ports on the front of the block to which the water pump attaches. Reassemble and STILL RUNS HOT to 200+ degrees.

(3) Remove thermostat and restart boat. Thermostat max's out at 140 degrees. Large hose from thermostat housing to water pump is now cool not hot as previously. Manifolds/risers slightly warm to touch - previously cold.

OK, so what gives? Defective thermostat. Damaged water pump??

Any thoughts???
 

Bronc Rider

Petty Officer 1st Class
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Sep 1, 2009
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Re: Volvo 4.3/overheating/pulled thermostat - help!

What temp is the new thermostat rated at?
 

harleyfool

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Re: Volvo 4.3/overheating/pulled thermostat - help!

"160" stamped on the thermostat - assume that means 160 degrees.
 

fuzzybob

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Oct 26, 2008
Messages
213
Re: Volvo 4.3/overheating/pulled thermostat - help!

harley, not trying to be a smart a--- or anything but are you sure the t-stat is not upside down?
 

harleyfool

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Re: Volvo 4.3/overheating/pulled thermostat - help!

Checked that - but it only fits in one direction - spring side faces down toward block.
 

harleyfool

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Jun 7, 2009
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Re: Volvo 4.3/overheating/pulled thermostat - help!

So.. running at 1000 rpm on muffs with no thermostat installed the engine temp level off at 140 degrees. Is this reasonable or should the temp have been lower???
 

mikeneal

Senior Chief Petty Officer
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Jan 28, 2004
Messages
710
Re: Volvo 4.3/overheating/pulled thermostat - help!

I would suspect lower. Does it have a power steering cooler? That is common place for impeller vanes to collect I think.
 

bruceb58

Supreme Mariner
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Mar 5, 2006
Messages
30,454
Re: Volvo 4.3/overheating/pulled thermostat - help!

I would think lower.

Next thing you should do is get an IR temp measurement gun and shoot it at the thermostat housing, the inlet of the circulating pump and the temp sensor area and see what temps you are actually running at. Could easily be your gauge is off. With the thermostat in or out, can you put your hands on the risers and do they feel just warm? If they are just warm, you are probably getting enough water flow. I just started my 7.4L engine last night and at a fast idle, they get up to 110 and my thermo housing or right behind it where the temp sensor is located, runs 140. I have a 140 thermostat in my engine.
 

harleyfool

Seaman Apprentice
Joined
Jun 7, 2009
Messages
35
Re: Volvo 4.3/overheating/pulled thermostat - help!

A good thought but, as far as I know the power steering cooler is BEFORE the sea pump - so I don't think the impeller bits would be there.

I will track down a IR gun and report back ... :)

So @idle and no thermostat is 140 degrees higher temp than expected - if so why would it be higher?
 
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