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What is considered overheating?


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I installed a new impeller this spring, but don't know when the last time the thermostat was changed. Per the temp gauge, I am getting between 170° and 180° at idle, and 160° or a touch cooler at cruising. What temp is hot enough to shut it down and start looking for problems?

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Shouldn't really be running over 160, but 180 isn't going to kill it either.  If I was seeing 180 at idle I'd be checking the impeller (regardless of the last time it was replaced) and then likely replacing the thermostat too.

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IIWM, once it gets outside of what I am normally seeing "I would be on it like a spider monkey" checking to see how many impeller vanes are stuck in my trans cooler. 4 7mm/5/16 inch nuts are too easy to get to and remove at least on my LSV.

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7 minutes ago, oldjeep said:

Shouldn't really be running over 160, but 180 isn't going to kill it either.  If I was seeing 180 at idle I'd be checking the impeller (regardless of the last time it was replaced) and then likely replacing the thermostat too.

It doesn't actually hit 180. The gauge has ticks in increments of 20, with 160 being marked and 240 being marked  (i'm sure you all know what the bu multi-gauge looks like). Anyway, on idle, the needle gets above 160, but stays below the next mark, which would be 180. Cruising it stays on 160 or slightly below. Is there any amount of leeway in the accuracy of the gauge? 

Also, the gauge needles are supposed to sweep on ignition power, correct? I noticed yesterday that the oil pressure and temperature needles wouldn't sweep. They just kinda wiggled, but the fuel and voltage needles did a full sweep. Both oil pressure and temp readouts looked normal during operation though. Oh, and there was one runight where the temp didn't read at all. Turned ignition off and back on, and no more problems the rest of the day. Am I on the way to a gremlin?

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The oil pressure fluctuates with engine speed, which I guess it should. The gauge in my Chevy truck fluctuates with engine speed also. The boat reads 40psi at idle can get close to 80psi at high rpm. That matches up pretty closely to what my truck with the 5.3l reads.

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@Chatty21VLX:  To your title question, overheating would be a bit under 210 degrees F as that is where water boils and in our boats there is very little pressure to provide any water boiling point cushion (water under pressure raises the boiling point).  Your car as an example operates at ~210 deg F for a typical GM product with a small block V8 but is has both pressure and coolant to raise the fluid boiling point to roughly 230-240 deg F.

What you are seeing with the temperature fluctuations is a weak draw by your impeller and thus not providing as much low speed water flow as the previous impeller.  Once the impeller is sped up via engine speed increase, you push enough water to the circulation pump to keep the engine at the thermostat set point.  Reason for weak draw is probably too much side clearance in the impeller or weak blades, I have seen that quite a bit with different (new) impellers.  Seems like a bit of a crapshoot in my experience to consistently get good ones.

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@Chatty21VLX:  I would not waste my time swapping your latest one, I have run with impellers that do what you indicate for the balance of the year and maybe consider changing for the next season.  I always pull pump and remove the impeller for winter storage.  A new one may do exactly the same thing!  What I would do, is check the inlet side of the transmission cooler for debris and the water separator as those could also be a restriction point that results in the same symptoms.

I always enjoy putting in a new impeller that is less efficient than the old used one I pulled out.:salute:

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3 hours ago, Chatty21VLX said:

Also, the gauge needles are supposed to sweep on ignition power, correct? I noticed yesterday that the oil pressure and temperature needles wouldn't sweep. They just kinda wiggled, but the fuel and voltage needles did a full sweep.

I'm positive that's what mine do, just a noise and wiggle-wiggle then go to their proper readout, but IIRC volts go UP to its readout, whereas water/oil do the swing?  Now you're gonna make me record it to be sure...anyway 180 degrees isn't anything to get worried about.  The 160 temp is to prevent corrosion from minerals in the fresh water.  It's all above my head but minerals in the water can accelerate corrosion above 160, and in salt water above 140 degrees.  Temp probes and thermostats are cheap, I would just replace them for peace of mind, and make sure the impeller looks good and transmission cooler screen is clear of debris, but you certainly didn't do any damage. 

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