Mariner 150 Overheating

[sonnyboy80]

My 1989 150 Mariner MagnumII overheats in rough water. While it seems to run a little on the "warm" side in smooth water, it doesn't completely overheat and the warning beeper doesn't come on. When it's warming up, the needle on the temp guage goes to the "edge" of the "hot zone" before it kicks back and starts to cool. The boat was in dry storage for a year before I actually used it on the water.<br /><br />Yesterday, I ran it for 20 miles hard (over 5000 RPM's) with no overheating. On my return trip, the wind had started to blow some and the water became choppy. Within three minutes, the temperature gauge slowly advanced to the right and the warning buzzer came on. (It has done this on the last two outings and only in rough water - 1-2 ft. waves) As soon as I made it to smooth water again, it was fine. (I stopped the engine immediately when the buzzer sounded and let it cool first)<br /><br />I had the engine trimmed down when it ran hot and when I was running it hard I varied the trim with no problem. I don't have a special jack plate or anything like that. The engine is mounted directly to the transom in a standard type configuration. The engine will idle forever and not overheat and there's a steady stream coming out of the telltale even when it's overheating in rough water. The temperature guage runs at about 3/4 and I'd like it to be straight up under operation, but I suspect this doesn't mean anything anyway. The telltale stream starts to emit from the engine at about three minutes idle time and continues throughout the problem.<br /><br />What do you think? Impeller? Thermostats? What?<br /><br />Help!<br /><br />Clayton

 

[AndyL]

Re: Mariner 150 Overheating

G'day Clayton.<br /><br />I had an overheating problem on a 135XL which is basically the same engine and after changing thermostats and impellers the fault was traced to the "popper" valve which regulates water pressure in the engine apparently. It is accessed via the lower cowling. My problem was a general lack of water out of the tell tale unless I was running at speed. Hope this may help.

 

[sonnyboy80]

Re: Mariner 150 Overheating

Thanks Andyl! I'm getting a steady stream of water out of the telltale even when the engine is registering hot and the buzzer is going off. I'll check the poppet valve also though. This is a frustrating problem because it only gets hot in choppy water...not when idling or running wide open in calm water. I'm sure it has something to do with the engine coming out of the water for short milliseconds in rough water and probably is caused by not enough water pressure in the top part of the engine during this time...now if I can just find what's causing that! Thanks again!<br />Clayton

 

[AndyL]

Re: Mariner 150 Overheating

Hi again Clayton,<br />The local agents here did tell me that the top cylinders do run hotter and that is why the sensors are mounted there. The port side one I belive is wired through the module and to the alarm side, the starboard one is wired to the temp guage. The blocks on the V6 have quite a huge water capacity and thus if the popper valve is weak the pump cannot maintain enough head in the engine to effect good cooling especially to the upper cylinders. Another worry is leakage at the block end of the water pump discharge allowing cooling water to drop back down the exhaust. As I undrstand it you would have to remove the powerhead to replace the O- ring seal. We could not get the powerhead off mine as the four front bolts were solid.

 

[sonnyboy80]

Re: Mariner 150 Overheating

Hi Andyl!<br /><br />Yesterday, I bought a new water pump kit, two new t-stats and a poppet valve kit. I'm going to install (or try to install) them this weekend.<br /><br />The mechanic swears that if my poppet valve was not working properly, a steady stream of water would shoot into the engine compartment (inside the cowling) and that this is designed this way on purpose to let me know there's a problem.<br /><br />I guess my question is: How would I know water is squirting inside the cowling unless I took it off for some reason? <br /><br />So far as I can tell, no water has been "squirting" in there but I agree with your theory and I think it might be a combination of the poppet valve being weak and the impeller needing replacing. We'll see, I guess.<br /><br />I still don't understand why it only happens in rough water unless it IS the poppet valve not holding enough water inside the engine for short periods.<br /><br />I'll let you know how it all comes out.<br /><br />Thanks for your response!<br /><br />Clayton

 

[AndyL]

Re: Mariner 150 Overheating

G'day again. Bet the part supplier was pleased to see you!! For your information my poppet valve never leaked just the spring was tired. As mine is XL it has a higher head to maintain and hence any weakening of the spring causes pressure loss. The best of luck, and will be pleased to hear the result of your labours.<br />Andy

 

[sonnyboy80]

Re: Mariner 150 Overheating

Hi Andy!<br /><br />Well, I did the dirty deed. I changed both thermostats and replaced the impeller and housing. What I found was...the old impeller had two blades completely broken away. I wonder why it wasn't overheating at idle!!<br /><br />Good thing I had the warning buzzer...I would have burned it up for sure, since there was no indication that anything was wrong. Even the telltale was working fine.<br /><br />Anyway, it's great now! I took it out and it doesn't even warm up to half way. (Everyone told me it was normal for it to run at 3/4 hot) <br /><br />Thanks for your input and replies. Oh, I put the impeller in a different way than I was instructed...I put it in the housing first, then slid it over the shaft and lock pin. That seemed the easiest way to do it to me.<br /><br />Thanks again!<br />Clayton