1996 Mercruiser Alpha 1 Gen II 4.3L Water Pump

[Bummer1959]

Hey all! I own a 1996 Larson Mercruiser Alpha 1 Gen II 4.3L engine that continues to overheat. I have checked the impellor pump and that is in good shape, replaced the thermostat, as well as looked at the steering fluid cooler for obstructions, however, the engine continues to overheat. I have been told by a dealer that it is the engine water pump, although no visible leaking is present (he indicated that wouldn't necessarily be the case). I have ordered a water pump, however, any thoughts on if I headed down the right path here? Any other chonic areas of obstruction I should be checking as well?

Also, any protocols I need to follow or nice to know procedures in changing out the engine water pump?

Many thanks all!

 

[Bt Doctur]

loosen/remove the large hose, remove 4 bolts, and replace pump.
"~~I have checked the impellor pump "
2 years or more it gets replaced, regardless of condition.do a full pump kit including the base , is the connecting hose at the transom kinked? They have been known to collapse internally too

 

[thumpar]

Have you checked the flow to the thermostat housing? Circ pumps don't fail too often on that engine.

 

[Howard Sterndrive]

If the circ pump is turning, I doubt that's the cause of overheat.
Which way is it overheating:
at idle? or on plane over 3000rpm?

 

[achris]

Just been chasing a slightly elevated temperature problem on my engine. Up to about 6 months ago the temp gauge was always just above 1/4 (no degree markings on my gauge, just marks at cold, 1/4, 1/2, 3/4 and HOT)... No 'overheat' as defined by the ECU, but when pushing it (more than 3500 rpm) the temp would slowly work its way to just below 1/2... To me, that is the first sign of something not right. I changed the exhaust elbows (because they needed to be changed anyway), checked the incoming water check valve, dropped the gear housing off the drive and replaced the gaskets on the water pump base plate. Impeller was pristine, and I did use alignment pins to re-install the housing, and the special tool to set the v-seal on the top if the housing. I pulled the thermostat and checked it in a pan of hot water on the stove, with a proper laboratory thermometer, and an IR gun... Nothing! Everything is as it should be...??? so, I have bought a new thermostat and all the gaskets and installed them. I was thinking about taking the boat out this morning, but the weather isn't nice (cold, raining)... Maybe next week.

Point being, if it's not the thermostat, the next and only thing left is the engine circ pump.... and short of the impeller being completely gone, I can't see that being a problem... But for the cost of the gaskets (about 50c) it's worth pulling off and checking....

Chris......

 

[Howard Sterndrive]

over 3K rpm overheat? Put a clear hose before the tstat and watch for exhaust gas in the incoming water.

I have an old 1964 Volvo V8 AQ180. Guess what..No circ pump.Volvo knew it did nothing. The Jabsco impeller does just fine.The only reason the circ pumps are on these car motors is because the automotive ones do. Probably helps cool the rear cylinders a bit too.

 

[Bummer1959]

Thanks all! I am very new to these forums, and it took me a bit to find my own post. I will have to work at that. Anyway, my boat is overheating at an idle. After having the impeller checked, the mechanic took the boat out and it was higher temps at an idle. I was simply in the yard testing it with the muffs on and at first it didn't seem to get to an. Idle temp, but when I looked away the temp suddenly spiked and the alarm sounded. I have purchased a new water pump, but I'll still be checking each of these suggestions as we'll. I've also watched a couple of related videos that showed similar checks for flow and the like, as you have suggested too, so that is the current plan. I'll try and check the thermostat as well, as I also have seen bad thermostats out of the package too! The pump itself looks simple enough I guess, but need to find some info on the torque required for the bolts, or just wing it. Thank you all again, and I'll get a post with the results. I'm used to keeping my stuff running right, so this will drive me until it's back to turn-key condition again!

 

[Bummer1959]

Greetings All! Well, I installed the water pump (the engine circulating pump) and it appears to be a success! I don't believe I ever say that much water come out of the exhaust since I started doing my own winterizing of the engine. Amazing, I still cannot tell what was entirely wrong with the last pump, however, upon inspection there was some evidence of leaking on the housing, but in tearing it down a bit (back plate), there really wasn't anything castastrophic to make note of (must have been the seal). The temp guage and water temp did not rise considerably at first, however, I was using fairly cold water to flush, but eventually it started to rise to about 140 degrees (actually I'm pretty sure I knew when the thermostat popped) and then at approximately 1000 rpms, the temp rose to about 180 and sort of settled down there. I did not run it much longer after that. I hope this is the spec in general, but the real test will be in the water under a load, and, still hoping there was no real damage to the engine from overheating last year. With some luck, this will have solved my boat gremlin, now I get to move on to my motorcycle non-starting gremlin and then my no left blinker on my Ford when hauling a trailer gremlin. They each have their own forums too!

I have to also say by the way, I love these forums, so helpful and can be significant money savers too. I hope to pay someone back with some advice one day!

 

[Bondo]

Greetings All! Well, I installed the water pump (the engine circulating pump) and it appears to be a success! I don't believe I ever say that much water come out of the exhaust since I started doing my own winterizing of the engine. Amazing, I still cannot tell what was entirely wrong with the last pump, however, upon inspection there was some evidence of leaking on the housing, but in tearing it down a bit (back plate), there really wasn't anything castastrophic to make note of (must have been the seal). The temp guage and water temp did not rise considerably at first, however, I was using fairly cold water to flush, but eventually it started to rise to about 140 degrees (actually I'm pretty sure I knew when the thermostat popped) and then at approximately 1000 rpms, the temp rose to about 180 and sort of settled down there. I did not run it much longer after that. I hope this is the spec in general, but the real test will be in the water under a load, and, still hoping there was no real damage to the engine from overheating last year. With some luck, this will have solved my boat gremlin, now I get to move on to my motorcycle non-starting gremlin and then my no left blinker on my Ford when hauling a trailer gremlin. They each have their own forums too!

I have to also say by the way, I love these forums, so helpful and can be significant money savers too. I hope to pay someone back with some advice one day!

Ayuh,.... Welcome Aboard,.... I'm thinkin' there was Nothin' wrong with the pump ya took off,...... 180° is Waayyy to High,.... Ya oughta be seein' 140° or 160° dependin' on the T-stat in it,....At 1000 rpms, ya should see the temp fluctuate from just below the T-stat's rated temp, to just above it,... I'd return to the Impeller pump, 'n replace the Whole kit, housin', 'n all,....
While ya got the lower off, 'n changin' the pump,... Pull the 1" hose off the T-stat housin', that comes from the impeller pump,... Hook it to yer garden hose, 'n Back-flush it to see if any debris is causin' yer problem,....

 

[Bummer1959]

Back on the net again! Sorry for the delay in providing an update. Well, no luck as of yet, engine overheated to 240 and that gets me all the more worried. New engine circulating pump, new thermostat and good looking impeller pump. Must be a blockage or as some may suggest, a head gasket. I hope for the latter. I do need to go back and return to the impeller pump as you suggest, but do some back-flushing and other checks as well. Once again, more to follow..............