overheating &won't idle

[vicsponjr]

Hey guys.<br />Ihave a 19'85 citation, 3.7 merc with alpha drive. After overheating at the end of last season I had the impeller replaced. Since then it has been idling at 160, when I start running it goes up to 175-180. Yesterday I was out with 8 people (including myself) and hit a sandbar. I don't think the drive hit but I'm sure I kicked up a lot of crap. Pushed the boat off and got back under way and it went up to 225 and pushing before I slowed it down. Ilet it cool down and topped it off (didn't lose much coolant)and it came back up to 225 so I limped it back home. While in my no wake zone which is about a 10- 15minute ride it cooled down to 175 but then the second problem kicked in. The boat, after a couple of minutes of riding at idle starts running rough and then stalls. Start it back up and it does the same thing and I usually wind up just drifting to the dock. The boat runs great when moving above idle. in the beginning of the season I had someone work on the nuetral stall switch. He also messed with the air mix on the carb. I know I have a cable adjust problem too because when shifting into forward the rpm's start increasing just before engaging. I am going to start pulling the cooling system apart this morning to look for obstructions. Any feedback on any topics would be appreciated.

 

[rbezdon]

Re: overheating &won't idle

Victor,<br /><br />Sounds to me like you pushed the engine too far too hot and now you have a serious problem like a blown head gasket or something. You should never run an engine at 225. Shut it down and get a tow or wait several hours to cool it before trying again. I would start by pulling the plugs and examining them closely. Note what cylinder each came from. Also, run a compression test. This is all after you fix the water flow issue that caused the over heat in the first place.

 

[waterone1@aol.com]

Re: overheating &won't idle

You said that you lost some coolant....so we can assume that you have a heat exchanger. In my opinion, the first step would be to determine where the coolant is going. There are two possibilities, either into the cylinders (blown head gasket) or mixing with raw water and going out the exhaust. Pressure test the closed cooling side with a radiator pressure tester, it should hold about 15 lbs. If you loose pressure, see where the coolant is going. The other part of the equation is to pull the lower unit and inspect the raw water impellor as the sand may have damaged it. You also have a third problem, that would be the shift/throttle linkage.....if you ever thought about buying a service manual...now would be the time!

 

[vicsponjr]

Re: overheating &won't idle

Thanks for the reply. I tried to pick up a pressure tester yesterday but couldn't find one. Will ask around at work today. I bought a service manual but it is for 64-91 stern drives and doesn't give much detail. Do they have one specificly (?) for the 3.7 setup? I checked the heat exchanger and it looked new. Put it back together and ran it in the driveway and it ran at 150. I'm not going to take anything else apart till I water test it. I had 8 people in the boat that day, could it just be too much for this old motor? I noticed some blowby coming out of the oil fill cap, so the rings are probably going.

 

[Don S]

Re: overheating &won't idle

It may be the exhaust elbow is plugging up with rust and scale. This will slow down the water flow and cause your overheat.<br /><br />Aftermarket manuals don't help much on the 3.7L (aka 470 style engines).<br />Depending on your engine serial number (Don't go by boat year) your engine could either be in manual #3 or #8.<br /><br /> Merc Service Manuals

 

[vicsponjr]

Re: overheating &won't idle

Thanks again Don