www.iFourWinns.com

I have a 1998 Vista 258 with the 7.4 Gi engine. I bought the boat 4 years ago and it had raw water cooling so I had a closed cooling system added so I could run in salt water with less concern about engine corrosion. There were some issues with overheating the first year but the dealer that installed the system eventually addressed the issues and it ran fine for three years. I should mention that I replaced the impeller four years and several of the vanes were damaged but I was not able to find all the small pieces.

I took it out for a run last weekend and it overheated after about 45 minutes of moderate running (20-25 mph) just as I got back to the dock. I run it on muffs at home the next day and noticed that there was a leak from the seawater pump so I replaced it. I ran the engine again last night on muffs and it overheated at idle. Tonight, I ran the engine again on muffs for 25 minutes - the temp went up to normal and the needle stayed right on the center of the gauge so I shut it down. While it was running, I aimed an infrared thermometer at the thermostat housing and it read ~160F and the large hose running from the thermo housing to the heat exchanger read ~145F. I started it up again 30 minutes later and this time it overheated. I confirmed the overheating with an infrared thermometer which read 205 F when I shut it down. Here is the catch - the hose from the thermo body to the heat exchanger was reading ~110-115F -- cooler than when the engine was running normally. I thought 'defective thermostat' but I pulled it out and it opened and closed at ~165 in a pan of hot water on the stove. I am now stymied as to the cause and possible solutions.

Could it be a long lost piece of the impeller? Could the thermostat be failing to open intermittently? What else?

Thanks for your help.

salt water...clogged risers and manifolds...check their temps to see......usually 5 years is time to at least check...

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88 Four Winns 200 Horizon
4.3 OMC Cobra-4bbl
2002 Walker Bay 10/2012 Suzuki 2.5
2008 Walker Bay 8

1998 Jeep Grand Cherokee 4.0/Selectrac
2007 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

When I had the survey on my boat done a week ago the surveyor had one of these you might want to check it out. He said it was the simplest way to check if there were any hotspots in the engine manifold or risers, you just compare one manifold to the other and so on. It was pretty cool him taking all these temperature ranges and putting them on his laptop and comparing to the norms he had on file. I couldn't post the picture but it's a fairly simple tool that can save you thousands I am figuring if you catch something in the beginning stages as opposed to a full on failure. Infrared Thermometer will definitely be on my boats emergency repair kit. The surveyor had a fancier one but I am sure they all do the same thing do a little research I am doing the same will let you know which one I like the most.
Here is the URL http://www.omega.com/ppt/pptsc.asp?ref= ... XL450&Nav=

Found this one that is specifically made for the marine environment and I think it's cheaper. Once you get the problem fixed you take some baseline figures and you can always compare them to the temperatures you get if it starts overheating and I am pretty sure it will pinpoint the problem. Hope I helped you out Joe from Miami
http://www.boatradarsystem.com/boating- ... meter.html



Infrared Thermometers

Click for larger image.
$ 65.00 OSXL450

• Measurement Range -20 to 320ºC (-4 to 608ºF)

• Fixed 0.95 Emissivity

• 6:1 Field of View

• Auto Power-Off

• Backlit Display for Night Use

• Laser Circle/Dot Sight

• ºC/ºF Selectable


View related products - Temperature Meters

Jumped the gun on your post I just finished reading the whole post and you already did what I was telling you might help. Well I thought I was playing marine mechanic and I got excited hope you get it running cool.