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Wondering if anybody else has had this happen to them and any ideas on how to repair. 2012 Cobalt 296 Starboard side engine temp rises quickly when 1/2 throttled to over 200 degrees and engine goes into 2 alarms (coolant temp and exhaust temp) safety limp mode. However, when it is idled or low cruising speed it holds temp just fine to below 150 degrees. The funny part is that if we are out of the water on the lift and hooked up to a fresh water hose and throttle up then its fine and holds the temp. Only when we put it in the water and throttle up does the temperature jump. We checked for blockage for muck, weeds etc and its as clean as could be. Replaced the impeller pump, cleaned out flow control valve etc but doesn't seem to take care of the problem.

Still sounds like an impeller issue. You replaced the entire pump? When you replaced the impeller before were their any pieces broken off the impeller?

Yes, changed the entire pump. The impeller was in solid shape, no broken pieces, nothing that would show any kind of damage, Its strange. I'm thinking maybe a manifold sensor gone bad or something.

Sure sounds like something's restricting flow, and if forcing water works but the impeller doesn't it sounds like impeller. If the old impeller was good and the current one's relatively new but worked well for at least a while, I'd take a look at the belt/tensioner/pully to make sure the pump is actually spinning at full speed. Also, I seem to recall that if the loop isn't totally sealed (i.e., if you leave one of those little blue drain plugs out by accident) that the pump works a lot less efficiently, which sounds like the symptoms you're seeing - maybe check that they each have their rubber o-rings and are tight in place?

I'd also be tracing the rest of the water loop, pulling hoses and looking/blowing in them to see if I could find an easy answer, but it sounds like you've done some of that already.

Which engine do you have? Please do report back when you find out the solution!

I'll trace the loop and check all the seals. I'm flummoxed as well. I spent all day on it yesterday but might have to tip my cap and know when I'm bested, take the L and just bring it in to service. I'll update as soon as there is a conclusion. Thanks for the ideas.

Get an IR thermometer and shoot the thermostat housing to see what it's really at. Could also be a sticking thermostat although that wouldn't affect the exhaust.

You can also do the test that's in the manual wher you pull the hose coming from the water pump up to the thermostat housing at 1000 RPM and see it it pumps put the water amount to the specification. Would have to pull up the manual for that. I can look it up for mine.

Does this have closed loop cooling?

If so, everyone forgets the engine has its own water pump. I just had to replace mine.

Mswwi wrote: Tue Jul 27, 2021 9:39 pm Does this have closed loop cooling?

If so, everyone forgets the engine has its own water pump. I just had to replace mine.

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Hey mswwi. So glad you found us!

Any pics of your Cobalt?

And welcome aboard mate!
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