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View Full Version : Overcooling / not warming up


CiscoStu
08-22-2010, 09:26 PM
This past weekend I had an interesting problem... We were out for a pre-sunset ski, and my wife was driving to start with. When it was her turn to ski, I took the helm and fired it up. As I normally do, I checked all of the gauges to make sure everything was OK, and I noticed that the engine temp was way low... it read 80 deg.

We finished the night with a few more pulls, with the temp never going higher than 80.

I figured there was a problem with the thermostat, so I went to NAPA the next day and bought a new one - stainless steel 160deg. After I figured out the bizarre clamshell thermostat housing on the MCX, I put the new one in and fired it up - came up to temp within minutes. Now it runs about 10deg warmer than it used to, but I can live with that.

When I worked at NAPA in the 80s, they used to include a gasket with the thermostat - they don't do that anymore. I re-used the old one, making sure to check for leaks all weekend. I'll put it on the list for post-season repair.

Now I'm going back to NAPA to buy another one, and I'll keep it in the spare parts box as well...

oldairboater
08-22-2010, 09:31 PM
I would have installed a marine thermostat instead of automotive but it is your boat.

CiscoStu
08-22-2010, 09:40 PM
It is actually a marine thermostat, and it's stainless steel. NAPA just happens to carry it...

jconover
08-23-2010, 10:56 AM
Marine T-Stat's have a 'breather' hole to allow air pockets in the open cooling system to pass through the engine - automotive ones don't. At least, that's what I read here. It's not just stainless steel that makes the difference.

Air pockets can build up beneath the t-stat, causing it to not come up to temperature, and thus not open properly. The real risk here is that your engine is actually getting a lot hotter than you think, the t-stat is not opening up... possibly. I'd get the right t-stat before anything else.

CiscoStu
08-29-2010, 10:58 AM
Not sure what you mean by a 'breather' hole... Since it's a closed system after the raw water pump, there would be no way for air to purge regardless of a breather in the t-stat. The t-stat is completely enclosed inside the housing, so air would either flow through into the bypass, or into the motor. Either way, there are more air pockets inside the motor that also couldn't breathe. If there was any type of breather in the system at all, you would see steam coming out of it.

Even if the breather option were true, all it would do is bypass the t-stat. When the t-stat is closed, all it could do is allow water through. As soon as the t-stat opens, voila - air passes through anyway.

There may be some merit to the 'failsafe' thermostat - they fail wide open in case of overheating. This was not the type of thermostat that was in the boat originally, nor is it the tpye I installed.

So I was at my dealer yesterday looking for a new winch, and I asked the question... Automotive or Indmar t-stat. The response: "We use what you got from NAPA", to the exact same part number. He laughed at the idea of a 'marine thermostat'. Recommendation was to go with the best stainless steel t-stat you can find.

1985 Skiier
08-29-2010, 12:21 PM
I am not sure if Mastercraft recomends the wholes but Marine Power recomends using one like this. Three wholeshttp://i1228.photobucket.com/albums/ee443/Masrtercraft/IMG_3224.jpg

The wholes can be drilled yourself

I bought a replacement for my River boat with a closed system and bought a Napa (Brass) and drilled wholes to match the old one. Works fine.

Don't have a closed system in my MC.

Cheers!

TX.X-30 fan
08-29-2010, 12:21 PM
I'm on year 5 with my non-"marine" amplifiers............

1985 Skiier
08-29-2010, 12:23 PM
Hey my non Marine Stereo works great too......

TX.X-30 fan
08-29-2010, 12:40 PM
Hey my non Marine Stereo works great too......




Clarion lost a channel after year 2 and put a good Alpine in and never looked back......:D

1985 Skiier
08-29-2010, 12:45 PM
I have three amps in my fishing boat (non Marine) the fish bite better with a little boom!

I keep a fishing rod in my MC too

TX.X-30 fan
08-29-2010, 01:05 PM
I have three amps in my fishing boat (non Marine) the fish bite better with a little boom!

I keep a fishing rod in my MC too




NASCAR fan??.........:D

oldairboater
08-29-2010, 10:19 PM
Old trick on our boats that we carried over from building high hp engines back when thermostats were not as reliable. I still do it to my other boats and I did it to my Prostar. We drilled three or four holes in the thermostat base as a bypass in case the thermostat sticks closed. Too many holes or too big of holes defeats the thermostat. Just enough holes of the right size means the engine warms up slow but you don't see temperature spikes from the thermostat cycling. Some of the boats I run now have remote mounted radiators and overflow tanks which can trap air on a thermostat and in the goose neck. Have to be really careful when bleeding these systems. I might be over cautious and a little superstitious in my practices but you don't see me posting on here that my engine will not start hot, my block is cracked, my heads are warped, or my mechanic who does all of the big jobs just bought a new Mercedes.

CiscoStu
08-30-2010, 12:00 AM
Here is the damaged thermostat. You can see a little chunk stuck in the crack, holding it open. This opening is *almost* big enough for a piece of paper to fit through, and it goes about half-way around the t-stat (180 degrees). This tiny little opening was enough to cause my motor to not heat up over 80deg.

The chunk appears to be either a seed from a weed in the lake, of which there are lots, or a tiny little piece of weed stalk. Either way, it's in there good. The scratch marks just to the right of the chunk are from a screwdriver, trying to pry it open.

61300

Dad 2 3
08-30-2010, 12:40 AM
Previous thread covering the topic of marine thermostats and the reason for vent holes.

http://www.mastercraft.com/teamtalk/showthread.php?t=36665