Overheating problem?

[scottatwork]

I've got an interesting situation here.<br /><br />1986 Bayliner, Volvo AQ-131/275<br /><br />Last year during winterization I put a new prop on my boat - if you recall I had a 21" pitch prop and ran at 25mph at 3500rpm - TOO SLOW><br /><br />Well upon de-winterizing the boat and running it, I found the sea-water pipe under the exhaust man ifold to be leaking AT the heat exchanger.<br />I took it out, cleaned all the seals which looked NEW, I have a new one and I can't tell them apart. Plus the previous owner had used blue RTV on the plastic coupler on the heat exchanger so this has been an issue somewhere.<br /><br />Anyway the engine ran fine, warmed it up with a hose on it, everything held and looked good.<br /><br />So yesterday I took the boat out, ran it until it was warm and all was well. I was in my small race boat and my brother in law was d riving the bayliner. We got about 7 miles and he slowed down so I went back to see what was up and he said the carbeurator was backfiring.......I had told him to watch the temp guage but after we limped the boat back to the nearest dock he said he forgot to check it.<br /><br />I ended up taking my small race boat back to get the truck and trailer.<br /><br /><br />I get the boat home and start it to flush it, and yeah there's a 1/4" stream of water coming out, maybe a little less. I brought it up to temp to see if it would climb ab ove the 175 mark but it did not.<br /><br />I could not reproduce this in the driveway.<br /><br />Now the reason teh prop came up is because with the new prop the boat ran at 35mph at 5500 rpm......and it hasn't run that way in many many years by the look of things.......<br /><br />It starts and run easier now but what happened?<br /><br />Oil is clean, no head gasket issues etc........why would it backfire through the carb except as most engines do when they vapor lock?<br /><br /><br />Thanks - frustrated in Bremerton.<br /><br /><br />BTW - if anyone is from bremerton - that was me in the red white and blue bathtub between Silverdale and the Turner Joy <br /><br />Scott

 

[mkast]

Re: Overheating problem?

I might be wrong, 5500 sounds too high for Wide Open Throttle.<br />As far as temp in the driveway, no load on the engine.

 

[scottatwork]

Re: Overheating problem?

So maybe that's all there was, it overheated?<br /><br />I would not have run it that hard for long, although I did run it up to 5500 but when I was checking it out I kept it about 5k.<br /><br />I went from a 14x21" pitch to a 14x17" pitch - the guys at Michigan propeller told me that was the suggested prop for this boat, and the 14x21 ran me at 3500rpm.<br /><br />I believe WOT should be 4800.....maybe I need to go to a 19" pitch.

 

[Haut Medoc]

Re: Overheating problem?

Scott you were getting 3500 out of the 21 & 5500 out of the 17? <br />Something does not sound kosher...<br />You should not get that wide a range between the two pitches.....<br />For now, stick with the 17 & don't exceed your WOT spec.....<br />Have you changed your water/ fuel separater?<br />Water can give you a backfire...<br />MKast is right, no load on the engine, it ain't really working to get the rpm's up in the drive way......JK

 

[scottatwork]

Re: Overheating problem?

Thanks guys - I do NOT have a water separator , but I will by next weekend!!! I've been meaning to do it!!! <br /><br />Yeah the 21 gave me 3500, maybe 3800 max, hmmmm I don't recall it ever going to 4000rpm.....<br />But the 17 would have gone up to 5800 if I let it.....<br /><br /><br />I will use the manual WOT setting then, no higher than 3/4 throttle, that works and it's a brand new not scratched prop, so I'll get some use out of it and use a 19 next time!!<br /><br />Preciate all the input guys!!