NYW

We sold a 2005 400SS Formula to a customer in Europe and they have issues with the port engine throwing the alarm. The engines are the 496 Mag HO's. Accorning to the Rinda scanner it's both the port and stb side exhaust manifolds overheating in the port engine. The raw waterpump impeller is new, the thermostat is the correct one and new and it looks like the raw water is circulating fine when looking at the through hull exhaust when it's open. The overheating happens only on higher RMP's after about 10 minutes. The temperature gauge it self goes only to about 195 degrees but then the alarm goes off. When they idle and let it cool down it actually goes all the way down to about 155 degrees. The Stb engine stays at steady 180 degrees all the time, idle or high Rpm's. The boat is in Europe so we have no way to go and check it our selves but we would like to help the customer out. Does anyone have any experience in something like this? The boat had about 140 hours when he got it and this started right away. All the help and ideas are welcome. Thanks!

Sydwayz

Did it ever have an impeller let loose? It sounds like there may be obstructions in the raw water cooling system. Perhaps it has not been flushed well.

I'd start by pulling all the hoses and freeze plugs and doing a thorough back flush and downward flush, and see if that helps.

NYW

I would suspect that they haven't flushed the system properly. That would explain the high rpm overheating. What still puzzles me is the low rpm related low running temp. These closed cooled engines are supposed to run steady temps, aren't they? Maybe the lower coolant temp at idle is a separate issue. It's a wild goose chase to do this from the other side of the world but where the boat is, there's nobody really educated enough with these new engines. Thanks for the reply.

Raylar

Remember that in a lot of places in Europe, especially at his time of year the water temps can be very cold so its not uncommon to see an engine with a 165 degree thermostat at 155 degress or so especially on non calibrated dash guages. Under load the engine should rise up to 165 degrees to 175 degrees if everything is working well in the cooling system and the guages are somewhat accurate. The scan tool will show the computers read on ECT temps accuratly.
As for the one engine warming the exhaust manifolds past the guardian temp limits, it could be that some debris is in the system and clogging the flow to the manifolds. a lot of boats seem to be sold without strainers and in Europe its common to see grasses and other debris that will go right through the pump tend to end up in the oil cooler, heat exchanger and manifolds and cause a reduced flow which under loads can raise the EMCT's up beyond the
programmed limits.
Also remember that we have seen some of these plastic EMCT sensors go bad and they are one Mercruiser part that is realitivly inexpensive at about $18 each.
I would have them take the ends off the heat exchanger, the hoses off the oil cooler and look for debris or clogs.
Glad to hear they have a scan tool so you can help isolate the problems quickly.
I would also recommend that a scan tool read the pressures in the raw systems on both engines and compare them to see if the raw pump may still have a reduced output pressure reading at higher rpms.
My current belief is that no one in Europe or the good old USA should be boating with a 496 or 525, sc700 or such without a scan tool or quick easy acess to one. Its the best $400 most boaters with these engines can spend!
Hope you find your gremlin soon! Does not sound like a big one to find!

Dave M

Now that's good advice! That' what I always tell people. They waste a lot of time trying to guess what the issue is.

My 496HO runs the same temp regardless of RPM or the sea water temp.

NYW

Thanks everyone. I will advice them to flush the whole system and also send them the new sensors. If they are that inexpensive they might as well change them to make sure that they are not the problem. The boat is not even in the water yet, the problems are all from last summer and they are going to launch the boat again and I just heard yesterday that they found out the problem last year. I'll keep you posted.