View Full Version : LT1 Thermostat or Impeller Problem

06-27-2005, 04:29 PM
I've read some past threads on the site about overheating and The thread on the 2000 PS190 overheating thread is very close to my situation. (97 P205 LT1, 300 hours) 2 weeks ago I put my boat in the water and the temp gauge rose to just over 180 degrees while warming up and then it flew down to around 140 degrees. I didn't think to much of it at the time, because I never noticed what the temp gauge read before the thermostat opened. This past saturday the gauge read 200 degrees before cooling down to around 140 and stays there for the rest of the day. To me, this sounds like a thermostat is taking to long to open up. But reading other posts on this board, replacing the impeller would fix the problem. I replaced impeller last year. I know these are low cost items, but I would like to know exactly what is wrong, so I know for the future. I'm going to go ahead and replace the impeller. I already have a spare. Here are my main questions.
What temp should the guage read before the thermstat opens and cools engine?
Can I get themostats at local auto shop for the LT1 engine, there are two, the 160 and the 143?
Do you think its a bad thermostat or a bad impeller?

Thanks for the help

06-27-2005, 05:07 PM
Just as a reference, my LTR engine runs at 160.

06-27-2005, 05:23 PM
get your thermostats from skidim.com so you get the correct ones. If your impeller should be replaced every spring no matter how many hours are on it. or your local dealer since you aren't far from him ask for Jeff

Engine Nut
06-27-2005, 05:34 PM
Sounds like you might have a "lazy" 160 degree thermostat that opens too slowly and then doesn't want to close down to keep the temp up. The engine should run close to 160 degrees after it has warmed up. Make sure that if tyou do replace the thermostat(s) that the 140 goes in the lower housing and the 160 goes into the upper housing. Also, the 160 is a special thermostat with bypass holes drilled into it to allow some water to pass by the thermostat before it opens.

Engine Nut

06-27-2005, 06:41 PM
What Engine Nut said. Boat should run at 160deg, depending on the accuracy of your temp sender.
The only time I notice the temp go up above that is after shutting down, the engine heats up to 180-200, and then drops right down after restarting.
The 160 tstat controls the engine water to the heads and block, so that's what you're reading on the guage. The 140 tstat controls the water going to the exhaust manifolds.

06-28-2005, 10:10 AM
Engine Nut and Thrall are correct...and save yourself some time and get the t-stats from an MC dealer...for some reason I couldn't get the an auto parts store model 160 degeree t-stat to work properly, even with a hole drilled in it. It looked identicle but didn't work properly.

Also make sure that the upper t-stat (the 160 degree) has the rubber gasket on it.

06-28-2005, 01:55 PM
Thanks for the advice. I've ordered the T-stats from skidim.

06-28-2005, 02:09 PM
while we have this t-stat thing going I replaced the 140 with at 160 on my 89 Tristar, I have noticed that we run a bit hot usually around 180. Does my changing the thermostat cause this? and it is a new impeller.

06-28-2005, 02:17 PM
replace the 160 with the 143 degree

lakes Rick
06-28-2005, 04:41 PM
If you have a Closed cooling system I would think 180 would be preferable.. My understanding is the cold water source is why you don't want too hot of a motor, unlike a CC system that heats up to a specified temp.....Cold water- hot engine= bad stuff......