Hey guys, I have a 496 ho. This spring it did raw water pump rebuild, new manifolds and all new gauges. Took it out yesterday for a ride and temp was creeping over 210 on the gauge. And actually got to 220 when running wot for a minute maybe. It would cool back to 205-210 while running at cruising speeds. Alarm never went off. Manifolds felt nice and cool plenty of water coming out exhaust and coolant hoses and exchanger were hot but not crazy hot. Like to me the thing did not feel like it was running that hot. Is it possible the new gauge is not reading correct. Where dose the ecm get its temp from. It must have its own sensor to set the alarm off correct? Should the alarm go off at like 200 regardless of what the gauge is reading? I replaced the stock lavorsi gauge with auto meter pro comp marine. Any help would be appreciated
thank you

sounds like a sender gauge incompatibility,,as for the ecu,,it has its own temp sensor,,its a 2 wire w/ yellow and black wires.

I believe #7 is for ecu and #8 for your gauge. Check with livorsi what sender of theirs is needed for your gauge

Thank you, so you believe the alarm would be going off if I was running at 210-220 correct. Autometer does have their own sender. I’m ordering that now. Hope this cures it
thanks again.

When was the last time you opened the heat exchanger, inspected, cleaned, and replaced the rubber end cap seals.
The end cap seals fail internally over time and then block cooling passages, which will cause hotter running temps.

When was the last time you replaced the coolant? What does the color look like? Is it still bright pink?
The pink coolant has to be replaced every 6-7 years, or when it starts to "silt" up, turn dark and metallic a bit.
This means coolant isn't flowing as well due to jus being old, and full of crud as it doesn't have a filter.
This will also cause hotter running temps. There have been a LOT of posts on this topic.

^ this... PLUS might want to check your power steering cooler on the back of the engine and flush it.. it can get clogged with debris and chunks of old impeller.

Seth,

Oil cooler is the first thing in the raw water tract after the seawater pump. That's where I found the debris on my engine while pulling it apart to rebuild. A full raw water backflush is always a good idea.

I fully second the input about the gaskets on the ends of the heat exchanger. I found mine to be almost entirely caved in. Between this and the oil cooler blocking off a significant amount of raw water flow, I was starting to run pretty warm. Change them. they are cheap and easy to replace.

Thanks. Brad.

If it was over 200*, you should have gotten an overheat alarm.
Need to run it with a scan tool to see what the actual temp is.

I'd suggest using an IR thermometer to help troubleshoot.

Griff is correct, the 496HO will go into limp mode if you were really running that hot.