raw water passage blocked?

[vicsponjr]

85 3.7 merc, alpha drive, closed cooling system. I was overheating so started checking for blockage at the outdrive. I disconnected the raw water hose at the heat exchanger and tried pushing water thru from the outdrive with the muffs but nothing comes out. Does the engine need to be running, or should I be able to force water past the pump?

 

[Chris1956]

Re: raw water passage blocked?

Vic, You need to run the motor for water to be pumped, however, it will be hard to tell if your waterflow is adequate based upon that test. If the impeller in the outdrive is 3-4 years old, or you ran thru some mud/sand recently, it likely needs to be replaced.<br /><br />I would also inspect the heat exchanger for blockage, and make sure the thermostat opens. For example, if the engine coolant is cool and the motor is running hot, it is likely a stuck thermostat.

 

[vicsponjr]

Re: raw water passage blocked?

Thanks Chris. the impeller is only a month old, I don't think I destroyed that yet. I just removed the heat exchanger and it is clean as a whistle. I'm wondering if I lost more coolant than I thought and that is why it was getting hot. This morning the overflow was empty and I didn't see any coolant in the reservoir. But why would I have lost coolant? oil looks oil, no coolant there. Wondering if i should put it back together and start it up or check the riser and elbows first.

 

[Chris1956]

Re: raw water passage blocked?

Well Vic, It's probably not the impeller. Time for a cylinder compression check to see if you blew a head gasket, or cracked the block. The coolant has to be going somewhere. if it is not the bilge, and not the oil pan, it must go overboard. Only a few ways to do that(leaky head gasket, cracked head, cracked exhaust manifold, cracked heat exchanger). You might pressure test the exchanger. Cars run their cooling system at 15 PSI. I don't know about FWC boats, but I would not exceed it.

 

[vicsponjr]

Re: raw water passage blocked?

just spent two hours driving around try to buy a radiator pressure tester. no luck. Did manage to pick up a timing light for $13 though.

 

[waterone1@aol.com]

Re: raw water passage blocked?

If the oil looks good and hasn't risen in level and you haven't noticed any smoke or running problems (hard to start, won't idle, etc.), then my bet is on bad heat exchanger. As Chris said above, pressure test the heat exchanger.

 

[vicsponjr]

Re: raw water passage blocked?

Idles fine except in gear, and even then its only when moving at idle for more than 5-10 minutes. I had someone work on the neatral stall switch about a month ago, and he messed with the air/fuel adjustment on the Quadrajet carb. But after a while idling it starts to sputter, run rough and even stall. I think it might be the float in the carb? I a going to put it back together and check the timing. Unfortunately I had to cut the coolant hose between the steering cooler and the exchanger to get it off. Of course I can't find anyone that sells 1 1/2" heater hose.

 

[vicsponjr]

Re: raw water passage blocked?

Ok, put it back together, ran at 150 consistenly in the driveway (i know, not a true test)Tried setting the timing, not as easy as I thought it would be. I'm gonna start a new thread for that.