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Old 01-12-2016, 07:45 AM
whiskeyriver's Avatar
whiskeyriver whiskeyriver is offline
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Odd Cooling Issue

Hey guys, I'm having an odd temp fluctuation with my 99 PS205 LTR running in cool/cold water. During the heat of summer when the river is warm my temp stays a pretty solid 160-f with the exception of the normal rise to 170-f after a hard run. The issue is in the early spring or late fall/ winter when the river gets to low 70's or less. The engine temp will increase at what seems like a normal rate then the t-stat will open and the temp will drop to 100. Then back up and back down. It will continue to do this indefinitely never settling down to a steady temp. The colder the water, the worse it will swing. I couldn't imagine running this thing in 40 degree water as some of you guys do. Here's a list of what I have done so far,
New OEM t-stat (twice)
New complete raw water pump.
Removed exhaust manifold and risers for inspection, (clean as a whistle)
Removed trans cooler for inspection, (clean as a whistle)
Removed all cooling hoses and inspected, (clean).
Anyone else experience this? Maybe some of you guys in the northern states where colder water is the norm? Thanks in advance.
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  #2  
Old 01-12-2016, 07:51 AM
snork snork is offline
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sounds like the only thing left to look into would be the temp sensor
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  #3  
Old 01-12-2016, 08:28 AM
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CruisinGA CruisinGA is offline
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Are you sure you've got the thermostat installed the right way?
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Old 01-12-2016, 08:58 AM
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Shaun R Shaun R is offline
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My guess would be an issue with the stat and it's letting too much cold water in. Mine is always run in 50-70 degree water and it will fluctuate, more so when running ballast. But it never drops below 100 while running.
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Old 01-12-2016, 09:17 AM
curver900 curver900 is offline
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what temp stat did you put in??? By OEM what do you mean? Where did you get the two you already tried? Did the first one do the same thing? Is it possible you got them from the same place and a possible bad batch?

If nothing else take it out and put it in water and use a thermometer to see when and how it opens in a pan of water... I don't know what else it could possibly be...
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Old 01-12-2016, 09:19 AM
TX.X-30 fan TX.X-30 fan is offline
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Has to be the thermostat.
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Old 01-12-2016, 09:43 AM
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whiskeyriver whiskeyriver is offline
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Quote:
Originally Posted by CruisinGA View Post
Are you sure you've got the thermostat installed the right way?
Thanks CGA, yes it's in correctly, mercury bulb down...

Quote:
Originally Posted by snork View Post
sounds like the only thing left to look into would be the temp sensor
The temp gauge has been replaced with an analog gauge, bypassing the mdc. It was like this when I bought it. I'm pretty sure it is at least relatively accurate as I can feel the temp change by placing my hand on the intake manifold, however this does spark a thought. I wonder if this temp swing is common and the mdc compensates for this, similar to a "slosh module" on an automotive fuel gauge? Still doesn't seem right though, that much temp fluctuation can't be good for the engine. Maybe some of you guys that have deleted your mdc and went with full analog gauges can chime in, do you see temp swings in cooler weather?
Any other ideas? I'm going to replace the circulation pump soon just for kicks but I can't imagine that causing this issue, I can run it hard in 100+ degree weather with no overheat issues at all.
I have determined what is happening is the thermostat is opening and allowing the cooler water to circulate thus cooling the engine and closing the t-stat over and over rather than actually regulating the water flow to maintain constant temp. Again, this only happens when the river temp is low. At or above high 70's engine temp is pretty solid.
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  #8  
Old 01-12-2016, 02:01 PM
curver900 curver900 is offline
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never seen it here... we have water in the 50's in the spring and fall mine runs at 160 all day long... slow/fast/idle...

Good luck
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  #9  
Old 01-12-2016, 02:53 PM
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Shaun R Shaun R is offline
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Doubt it would be a blockage issue as it's not overheating. Do you have another gauge you could use to verify the dash one is correct? Cannot remember on that block but the LT1 has two temp sensors, one by the pump and one in the side of the block. Gauge runs off the pump one and temp alarm runs off the block one. It's possible that cold water is making a temp swing like that, but also remember that oil cools the motor as well and that temp will not change as drastically and will help keep things warm. If you're sure the stat is installed correctly and functional, I would start chasing down electrical gremlins.
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  #10  
Old 01-12-2016, 05:55 PM
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whiskeyriver whiskeyriver is offline
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Thanks for the replies,

Quote:
Originally Posted by curver900 View Post
what temp stat did you put in??? By OEM what do you mean? Where did you get the two you already tried? Did the first one do the same thing? Is it possible you got them from the same place and a possible bad batch?
If nothing else take it out and put it in water and use a thermometer to see when and how it opens in a pan of water... I don't know what else it could possibly be...
I don't know if this issue was present with the t-stat that was in it when I bought the boat, I changed it for preventative measures before using the boat. The two that I installed are 160 degree that came from Rambo marine. OEM,(original equipment manufacturer). Never thought about a bad batch, could be possible. Can't hurt to try another new one. Also I did the pan on the stove thing with both and they started opening around 155 and we're fully open by 165. Kinda hard to control the rate of temperature increase on an electric stove lol. I didn't wait for the water to cool to see what temp it closed but they both began to close as soon as I took them out of the water.
Quote:
Originally Posted by TX.X-30 fan View Post
Has to be the thermostat.
Sure seems that way...
Quote:
Originally Posted by Shaun R View Post
My guess would be an issue with the stat and it's letting too much cold water in. Mine is always run in 50-70 degree water and it will fluctuate, more so when running ballast. But it never drops below 100 while running.
I agree, it's acts as if it's opening too quickly then the rush of cold water closes it. Sounds like yours is acting similar to mine, although I don't run ballast I have not noticed a difference with or without a skier. Mine never drops below 100 either.

Quote:
Originally Posted by Shaun R View Post
Doubt it would be a blockage issue as it's not overheating. Do you have another gauge you could use to verify the dash one is correct? Cannot remember on that block but the LT1 has two temp sensors, one by the pump and one in the side of the block. Gauge runs off the pump one and temp alarm runs off the block one. It's possible that cold water is making a temp swing like that, but also remember that oil cools the motor as well and that temp will not change as drastically and will help keep things warm. If you're sure the stat is installed correctly and functional, I would start chasing down electrical gremlins.
Good point on the oil. The LTR has three senders, one in the top of the intake (ECT) for the mefi, one in the cylinder head for the gauge and one in the front of the intake (below and to the left of the t-stat housing) for the temp alarm. I can't believe it would be electrical as I have verified the temp gauge with an infrared pyrometer, 160 on the gauge is 160 on the front of the cylinder head, (at least within a needle width on the gauge) and when the gauge drops you can feel the temp change by holding your hand on the t-stat housing. It's very noticeable.

Meanwhile, I am going to replace the circulation pump for preventative measures and will get another new t-stat. Maybe it is just a bad batch of t-stats. Everything works so flawlessly when the water is warm I just can't wrap my head around this issue. I'm still hoping someone has seen this before and has an explanation.
Thanks again guys.
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