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gourmatt
05-17-2010, 10:41 AM
Hi all -
This is my first post to TT, even though I've been an active reader for the past year. The motivation for my first post is an "Oh No" moment that I'm hoping some of you can give some insight to.

Background .... '96 Prostar 205 LT1 .... my first boat .... purchased last summer with 225 hours on it. Throughout last summer it ran great, no problems, but noticed after learning from this forum that it was running cool ... about 130 - 140.

After the season ended and I started to winterize it (by the way, I learned so much from this site on proper procedures -- what to do, what not to do -- thank you!) I found that the 143 deg t-stat was blocked open by what appeared to be bits of an old impeller. The impeller that was in there was not the culprit. It had no missing pieces. In any case, I figured that was the issue, but decided to replace both the 143 and 160 degree t-stats prior to the winter.

This spring I replaced the impeller just to be on the safe side. After I went through the whole dewinterizing process, the boat started right up with a fake-a-lake. I ran it for about 30 seconds just to make sure it was ok, then shut it down.

I put the boat in the water yesterday. I launched it at a neighbors ramp a couple doors down, then sped her over to my dock, where I idled it for about 10 minutes while chatting to a neighbor. Upon pulling away and giving some gas, it throttled back. I did this twice before looking down at my gauges and seeing the temp was PEGGED at 240. Obviously it was going into reduced power mode when I tried to accelerate. After my heart found its way out of my throat and I regained my senses, I immediately shut the engine off, opened the cowl and paddled my way back to the dock. The engine was hot enough that it was pinging and I could smell "hot", but not "burn".

After it cooled down a bit I started pulling hoses to see if there was a blockage. I knew the intake was not blocked and the transmission cooler was not blocked as I made a point to check and clean those this spring. Long story short, no blockages found anywhere. I then decided to take the 160 t-stat out of the engine as I remembered from this forum that some owners of early LT1's with overheating problems would do just that to keep the engine cool. Sure enough, the engine ran at 120ish. Suspect bad 160 t-stat at this point.

Now, curiosity got the best of me so I decided to put the t-stat in a pot of hot water on the stove. Darn thing opened right up! So at this point I'm scratching my head and dedcide, let's put it back in the boat. So I do that and the boat comes right up to 160 and stays there! I take her out for a check run and no problem! Temp stays right on 160 - 165 the whole time, up to full power. Also, no other obvious signs of damage from the overheat, though I'm not sure what I should be looking for in that regard.

So, I guess my question is two-fold. One, did I do any permanent damage to the engine and how would I know, and is there anything I can do about it? And two, what could have caused this? Do thermostats "stick" from time to time? Should I have removed them in the fall prior to winterizing? Or is there another culprit lurking somewhere?

And just to make a bad day worse, I winged the prop on a rock the end of my check ride (at idle). I didn't need that $300 anyway....

Sorry for the long post, but I thought the background and whole story would be helpful. Thanks in advance for your help.

JimN
05-17-2010, 11:14 AM
Hi all -
This is my first post to TT, even though I've been an active reader for the past year. The motivation for my first post is an "Oh No" moment that I'm hoping some of you can give some insight to.

Background .... '96 Prostar 205 LT1 .... my first boat .... purchased last summer with 225 hours on it. Throughout last summer it ran great, no problems, but noticed after learning from this forum that it was running cool ... about 130 - 140.

After the season ended and I started to winterize it (by the way, I learned so much from this site on proper procedures -- what to do, what not to do -- thank you!) I found that the 143 deg t-stat was blocked open by what appeared to be bits of an old impeller. The impeller that was in there was not the culprit. It had no missing pieces. In any case, I figured that was the issue, but decided to replace both the 143 and 160 degree t-stats prior to the winter.

This spring I replaced the impeller just to be on the safe side. After I went through the whole dewinterizing process, the boat started right up with a fake-a-lake. I ran it for about 30 seconds just to make sure it was ok, then shut it down.

I put the boat in the water yesterday. I launched it at a neighbors ramp a couple doors down, then sped her over to my dock, where I idled it for about 10 minutes while chatting to a neighbor. Upon pulling away and giving some gas, it throttled back. I did this twice before looking down at my gauges and seeing the temp was PEGGED at 240. Obviously it was going into reduced power mode when I tried to accelerate. After my heart found its way out of my throat and I regained my senses, I immediately shut the engine off, opened the cowl and paddled my way back to the dock. The engine was hot enough that it was pinging and I could smell "hot", but not "burn".

After it cooled down a bit I started pulling hoses to see if there was a blockage. I knew the intake was not blocked and the transmission cooler was not blocked as I made a point to check and clean those this spring. Long story short, no blockages found anywhere. I then decided to take the 160 t-stat out of the engine as I remembered from this forum that some owners of early LT1's with overheating problems would do just that to keep the engine cool. Sure enough, the engine ran at 120ish. Suspect bad 160 t-stat at this point.

Now, curiosity got the best of me so I decided to put the t-stat in a pot of hot water on the stove. Darn thing opened right up! So at this point I'm scratching my head and dedcide, let's put it back in the boat. So I do that and the boat comes right up to 160 and stays there! I take her out for a check run and no problem! Temp stays right on 160 - 165 the whole time, up to full power. Also, no other obvious signs of damage from the overheat, though I'm not sure what I should be looking for in that regard.

So, I guess my question is two-fold. One, did I do any permanent damage to the engine and how would I know, and is there anything I can do about it? And two, what could have caused this? Do thermostats "stick" from time to time? Should I have removed them in the fall prior to winterizing? Or is there another culprit lurking somewhere?

And just to make a bad day worse, I winged the prop on a rock the end of my check ride (at idle). I didn't need that $300 anyway....

Sorry for the long post, but I thought the background and whole story would be helpful. Thanks in advance for your help.

You have thin rubber lines that go from the heads to the exhaust manifolds. When it's idling, they have air in them and don't always bleed the air from the heads and this is why it overheated. If it did any damage, you'll know it soon enough but without seeing it and checking the compression, it's not possible to tell.

Never idle for long periods. If you need to and see the temperature creep up, put it in neutral and rev it, to get the temperature back to normal.

It's not a good thing to overheat a motor and send cold water into the motor when it's that hot. The temperature you see isn't the motor, it's the coolant. The motor is a lot hotter and hitting a hot motor with cold water can cause it to crack. Next time it shows overheat, let it cool and then start it.

gourmatt
05-17-2010, 02:26 PM
JimN - thanks for the reply and advice. It was probably a half hour between shutting it down and restarting it without the 160 deg t-stat, so hopefully no issues there. But with regard to the original overtemp, you say that if there is damage I'll know it soon enough. There weren't any obvious problems while running the motor during the check run. What does "soon enough" mean? Could it take a few hours of running to finally see any effects? And should I keep it docked until I can get a compression check done?

JimN
05-17-2010, 07:49 PM
JimN - thanks for the reply and advice. It was probably a half hour between shutting it down and restarting it without the 160 deg t-stat, so hopefully no issues there. But with regard to the original overtemp, you say that if there is damage I'll know it soon enough. There weren't any obvious problems while running the motor during the check run. What does "soon enough" mean? Could it take a few hours of running to finally see any effects? And should I keep it docked until I can get a compression check done?

You have aluminum heads and they don't like being overheated. I have seen many motors that overheated and never had a problem but I wouldn't make a habit of it. If you didn't see smoke coming from the motor, it's probably going to be fine without having to worry about it.