First Boat OVERHEATING Merc stern drive

[Baghs]

Okay, So I take the boat out for the first time this year. Ran with muffs the day before and all was well. On the lake the temp shot up off the charts real quick. Pulled the stat thinking maybe it went bad. Didn't fix the problem. Got it back home and did some checking. The freshwater pull seems to be supplying water with the muffs on. Not sure how much should be coming through but it is coming through. Could the pressure from the hose be pushing the water through. I am hoping it is the usual impeller on the stern pump. I didn't think or know to check that while on the water. Just how much pressue should I see with this thing pushing water with the muffs hooked up? If not the pump or the stat, (no water in crankcase), I don't think I have a cracked head or block, what else might I check? What is a good way to check the exaust water flow on these things? <br />Thanks for any help!!!!

 

[Haut Medoc]

Re: First Boat OVERHEATING Merc stern drive

You didn't say if you are raw water cooled or have a closed system....You should have a decent amount dumping from the exaust. Take the hose that feeds from the stern off and see how good the flow is (with the muffs on). There should be a good, strong flow.... If there is I would next look at the exaust elbows for restriction at the small ports that dump back out to the "Y".....

 

[ziggy]

Re: First Boat OVERHEATING Merc stern drive

when yer hooked up to yer muffs. prior to starting the engine ya will see the water shooting out the sides of the muffs. when ya start it, the water comeing out the side of the muffs should be much reduced. as in, it gettin sucked up from the sea water pump and heading twards the engine. this seems to be a pretty good sign to me that seawater pump is doing its thing. aslo water should be exiting the prop. on my old boat the water also exits up by the back of the drive. right next to the transom. i don't think the hose has enough pressure to get water going twards the engine if the impeller is bad. <br />as for other things. well, as j. said the riser could be restricted, or the manifolds, or the water passages in the block with rust and scale. i don't think that running w/o a t'stat is a good idea. look at some other threads about that going on right now. it won't help it keep cool w/o it and is likely to let it overheat apperently. if it's the impeller. broken peaces of the impeller can head up twards the block to and possibly block water passages. <br />just so ya know, i'm no boat mech, just joe boater with my own set of boat problmes. <br />oh, on the t'stat, ya can remove it and boil it in a pan with a thermometer. should start to open at 140 for an open cooling system, and be full open at 160. <br />if yer boat is a closed system. the heat exchanger will also be suspect from rust and scale also. restricted water passages again. not transefering the heat. good luck.....fixin boats sure is fun. and this forum will be most helpfull to you i think. bunch of great info here....

 

[Baghs]

Re: First Boat OVERHEATING Merc stern drive

Thanks for the tips guys. Parts shut down today so I can't get a new stat, did some other checking and the flow from all points seems to be good without the stat, but still gets hot. I did notice the riser on the starboard side seems to have some repairs (i.e. jb weld) on the underside of it. I still have a good flow from it on the other end so I am assuming it is working. Pleanty of water flowing from the prop/and stern drive. Oh, is it usual once you shut the motor down... for no water to be in the hose system, but when running flows great? Not sure if I have what you would call a open or closed system but I don't have a exchanger for sure. Pulls straight from stern water pump. <br />All points to a stat. The boat gets trashed if it isn't the t-stat LOL. Anyway, I can't thank you guys enough. And yes, I get more out of working on the damn thing than using it...that being said I would like to use it once in a while LOL. <br />Laters!

 

[Baghs]

Re: First Boat OVERHEATING Merc stern drive

Okay, Okay....looks like I am going crazy. Found a T stat today. Changed it out....engine still runs hot. Got up to about 180 before I shut it down. Seems to hold with trottle and get hotter when idle. Cracked open the lower unit and the impeller looks like it functions, going to replace it just for the hell of it. From other comments the heat risers are in possible question. Just how do those things fail? What should I look for and I have read some other information that the exaust shutters could be a problem. If I have pleanty of water out the exaust should I still consider this a issue or can I take them off the list? Thanks in advance.

 

[waterone1@aol.com]

Re: First Boat OVERHEATING Merc stern drive

Just in-case you are not familar with outdrive impellors, even if all of the rubber blades are there, if there is any curve to them after you remove the impellor and wait fifteen minutes, it needs to be replaced. A second thought would be to look at the water hose that connects the drive to the gimbal housing or transom. If this rubber hose develops cracks, it can leak water outside of the boat and loose water pressure to the engine.