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  #71  
Old 08-18-2013, 09:47 AM
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Traxx822 Traxx822 is online now
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Boat: Mastercraft, Maristar 200VRS, 1995, Indimar 5.7, My first MasterCraft
Location: Chicago SW sub
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Originally Posted by JimN View Post
You can't stop heat soak- it's caused by heat being lost from the hottest areas of the engine to the cooler areas. However, you can reduce the extreme temperature swing by idling for about a minute after a hard run, to get the temperature down to a normal level. The in-cylinder temperatures can exceed 1000F when running hard.
Thank Jim, I now understand heat soak thanks to this thread. My problem was the bad sensor for some reason causing my boat not to start with heatsoak. I now idle the boat for a while and monitor the temp while oof. Sometimes just letting it sit and heat up a bit, and then restarting (therefor refreshing the water that got heated) makes it all go away.

But my earlier problem was it wouldn't allow me to start if it got above about 180, now it starts at any temperature.

The sensor was clearly bad, some of you guys suggested ohms etc and we tested it as recommended and it was way off. So I think that was my issue.
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  #72  
Old 08-18-2013, 10:08 AM
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JimN JimN is offline
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Originally Posted by Traxx822 View Post
Thank Jim, I now understand heat soak thanks to this thread. My problem was the bad sensor for some reason causing my boat not to start with heatsoak. I now idle the boat for a while and monitor the temp while oof. Sometimes just letting it sit and heat up a bit, and then restarting (therefor refreshing the water that got heated) makes it all go away.

But my earlier problem was it wouldn't allow me to start if it got above about 180, now it starts at any temperature.

The sensor was clearly bad, some of you guys suggested ohms etc and we tested it as recommended and it was way off. So I think that was my issue.
Low resistance, or if it's intermittent, will definitely cause this. You could also open the throttle a bit if this happens again when rich exhaust is the key- if it smells like gasoline and it's very hot, something is wrong. If it doesn't smell like gas, it usually indicates simple heat soak. The people who did the calibrations and setup in the past would go to Arizona in summer to test at the GM Desert Proving Ground so they could work in real-world situations and they ended up increasing the overheat trigger temperature on the LT-1 to over 200F. It's a safe temperature for short-term and it eliminated a lot of hot-start problems for people with this engine. Hot air and warm water make this far more of a problem than in cooler water and if the boat has run in warm, shallow water in the SW US or some other place, the water temperature could be 90F, which makes cooling a very slow process.

Good to see the problem is gone.
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  #73  
Old 08-19-2013, 04:09 PM
carlbernhard carlbernhard is offline
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Join Date: Nov 2012
Boat: prostar 190 1989 351w
Location: south africa
Posts: 27
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Originally Posted by DAinAZ View Post
I believe I replaced the impeller 2 years ago when I used it in WV. I pulled it out last week and the vanes were flexible and looked good. I even had a new impeller in hand anticipating having to replace it. For 5 minutes work, I can put the new impeller in there this weekend and see if that helps. I can always keep the old impeller as my backup.

Something else to try. Thanks for the idea.
I had exactly the same problem on a 89 prostar. I had a welsh plug that had corroded through and leaky exhaust manifold gaskets. When i replaced the gaskets and the welsh plug the problem was better but not completely remedied. I would run through the entire cooling system as follows:
1.Check through hull pick up for debris
2. Check oil cooler for obstacles
3. check all pipes and hose clamps
4. Rebuild raw water pump ( or just replace impeller if bearings are fine and no leaks
5. Replace thermostat with correct t stat
6. Replace exhaust gaskets and riser manifold gaskets and check for corrosion
7. do a full compression test to identify potential head gasket damage

Replacement of the welsh plug and exhaust manifold gasket def improved the issue but did not completely solve it.
I have since pulled my engine apart for a complete rebuild ( due to a number of other unrelated issues ) and will post my findings after the entire system is running as new.
Good luck
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  #74  
Old 08-19-2013, 04:21 PM
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Originally Posted by DAinAZ View Post
After pulling someone, it would idle fine. I think it is gummed up a bit from sitting too long and not having been "winterized" at the time. I looked in the carb when it was running and nothing looked unusual, and also right after shutoff. Didn't see anything happening.

It has been doing this since starting it up after not running it for about 2 years.

Points, not electronic ignition.

Never rebuilt a carb. How long should it take/how difficult for someone who is mechanically inclined but never done it before?
Did you replace the impeller? Anyplace that has high ambient temperatures, I would be extra meticulous about the impeller, specifically and the cooling system, generally. Your high air AND water temps makes it a formula for disaster if the impeller has become weak and in high heat, that happens a lot faster than in a more moderate climate. Out there, a one year old impeller can act like it's more than three y.o. in Wisconsin.
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  #75  
Old 09-09-2013, 10:56 AM
BrianE BrianE is offline
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Join Date: Sep 2013
Boat: Mastercraft, Prostar 205, 1999, LTR
Location: Southeast
Posts: 2
Quote:
Originally Posted by JimN View Post
When was the last time you cleaned out your oil cooler and checked the impeller?
Thanks JimN for your constant guidance!... I noticed that my exhaust was steamy, exhaust manifold risers were hot and it didn't make sense as the impeller housing was cool. I replaced my impeller, but for whatever reason, I had thought my most recent check of my transmission cooler was more recent than actual. Sure enough, it was clogged up causing poor flow.

I have cleaned this out and have no more symptoms, but I am certain that I have run the boat for 22 hours without proper flow (what a jackass).

The boat is running well.
What other maintenance would you perform on the boat?
Oil change? Exhaust tube inspection?

Thanks again.
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  #76  
Old 09-09-2013, 05:23 PM
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JimN JimN is offline
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Originally Posted by BrianE View Post
Thanks JimN for your constant guidance!... I noticed that my exhaust was steamy, exhaust manifold risers were hot and it didn't make sense as the impeller housing was cool. I replaced my impeller, but for whatever reason, I had thought my most recent check of my transmission cooler was more recent than actual. Sure enough, it was clogged up causing poor flow.

I have cleaned this out and have no more symptoms, but I am certain that I have run the boat for 22 hours without proper flow (what a jackass).

The boat is running well.
What other maintenance would you perform on the boat?
Oil change? Exhaust tube inspection?

Thanks again.
If it was running hot, I would change the oil and filter because oil that has been exposed to temperature extremes loses some of its ability to lubricate and resistance to shear. These contribute to decrease the oil film, which is very important.I would squeeze the exhaust hoses to see if they have become soft and also look at the flappers to see if they have any damage. If they and the exhaust flanges aren't blistered, I would say that you dodged a bullet.
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  #77  
Old 09-17-2013, 11:22 PM
BrianE BrianE is offline
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Boat: Mastercraft, Prostar 205, 1999, LTR
Location: Southeast
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Quote:
Originally Posted by JimN View Post
If it was running hot, I would change the oil and filter because oil that has been exposed to temperature extremes loses some of its ability to lubricate and resistance to shear. These contribute to decrease the oil film, which is very important.I would squeeze the exhaust hoses to see if they have become soft and also look at the flappers to see if they have any damage. If they and the exhaust flanges aren't blistered, I would say that you dodged a bullet.
Thank you!
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