UPDATE! 5.7L Water Pump / TStat Replacement

[PeteHarris]

Mornin all --<br /><br /> I'm getting ready to replace the water circulating pump (front of the motor) and Thermostat on a 1994 5.7L Mercruiser. <br /><br /> Anyone have any tips / tricks / problems to watch for? I figured I'd clean out as much of the water jacket in the block as I can get at, if there's crud in there. I'm using a Sierra Water pump and a mercruiser TStat.<br /><br /> Thanks in advance.

 

[crazy charlie]

Re: UPDATE! 5.7L Water Pump / TStat Replacement

Most thermostats have gone to a plastic retainer so you cant just yank it out like the older brass ones.You will have to clean it up with a thin screwdriver or knife until you can see the outline of the retainer and work it out of the housing.Everything else is pretty straight forward.Charlie

 

[PeteHarris]

Re: UPDATE! 5.7L Water Pump / TStat Replacement

----SPROING----

 

[PeteHarris]

Re: UPDATE! 5.7L Water Pump / TStat Replacement

Well then --<br /><br /> I've changed the recirculating pump and thermostat relatively uneventfully. But I still have the same basic problem. <br /><br /> At idle (on muffs, haven't tried it on the water yet) the temp will gradually creep up to almost 200. Increasing RPM doesn't help. The Muffs are putting out more H20 than the impeller can suck up. If I shut the motor down for about 10 seconds, then restart the temp goes down to about 150 (norm) and holds there for about 5 minutes then gradually climbs back up. <br /><br /> I don't have check balls and seem to be getting good flow from the impeller. I pulled a hose from the TStat housing (Top, farthest forward, starboard side) that should be water direct from the impeller to the exhaust riser and got good flow (horizontal stream that cleared the oil covers ... about 2/3 the flow of a straight garden hose). The block is filling up with water and circulating so I don't suspect a blockage in the TStat housing. <br /><br /> My next step is to just replace the impeller (1 season old) ... any other thoughts??<br /><br /> Thanks for the sage advise.

 

[crazy charlie]

Re: UPDATE! 5.7L Water Pump / TStat Replacement

I would go with a new impeller and housing for the drive next.You can also open any brass drains on the risers or manifold and see if there is silt clogging it.Charlie

 

[Laddies]

Re: UPDATE! 5.7L Water Pump / TStat Replacement

Pete, if the elbows or the fittings on them are partally blocked it will do that, pull the hoses of the fitting and ck the flow, you can't leave them off very long without damageing rubber parts in the exhaust, but if you want to run it for a few minites you can hook a hose on the elbow fittings and run it to see if thats the problem but if it's a center riser this won't work

 

[rodbolt]

Re: UPDATE! 5.7L Water Pump / TStat Replacement

how hot are the risers getting? the t-stat housing with no check balls,the risers should stay cold at idle. remember if the risers clog water cannot exit and gets hot. but if the water pump is bad it wont pump either. so test everthing else then take a look at the manifolds/risers.

 

[PeteHarris]

Re: UPDATE! 5.7L Water Pump / TStat Replacement

The manifolds / risers get pretty warm, but no so hot that you can't keep a hand on them. Once it warms up, the water circulating pump inlet hose gets pretty warm, too. I know some of the water jacket water gets recirculated, but should that hose be hot also?