Rookie,

I see the visible difference. I guess the one I linked isn’t for the 496.

Kinda weird how the Amazon algorithm works. “I know you asked about the 496 thermostat, but what do you think of this one that fits the 4.3 V6?” :rolleyes:

Thanks. Brad.

Guys,

So, I will be dropping the boat off at Hilltop Monday morning, and they will have at it. just wanted to relay the behavior so I can relay any insight to them before they get started.

The boat runs consistently somewhere between 170-175°, as best I can estimate on the analog gauge. When I run it hard, it spikes to 180-185°, hovers there a while after coming off the throttle then slowly comes back down to 170° or so. Once above 160°, it never dips below it until I shut it off for a while. The needle on the gauge stays pretty calm and doesn't jump around. When we start it up after a good while not running, it takes it considerably more time to start flushing the port exhaust tip than the starboard, and we always get steam from the port exhaust when we settle in to an idle. The steam minimizes after a couple minutes, bet never really goes away. I do not hear any boiling after we shut it down. I get good output from the intercooler overboard. There is plenty of coolant in the reservoir for the closed side.

All-in-all, I'm not worried about the temp at this point, other than it seems to be creeping up a bit each time we take it out. And, much like the injector issue we eventually rooted out and solved, it's not that the behavior has changed, but that it seems to be changing, and I don't really want to find out how far it is going to go.

What do the minds of OSO have to say? Where to have Hilltop look first?

Thanks. Brad.

Have you ever chewed up your impeller? If so, did you check the fuel cooler, oil cooler and the heat exchanger for pieces? How old is your current impeller and pump housing?

Don,

We bought the boat in 2021 and have had the seawater impeller changed once (whole pump, actually) since then. The impeller was seriously showing its age, but it was all there, for the most part.

https://cimg3.ibsrv.net/gimg/www.off...c00cdbf00.jpeg

This pic was taken in March of '23, and the temp thing didn't start until this season. I have no worries about bits of the impeller plugging up the works. I'm guessing debris or an ailing T-stat is the culprit. I have faith in the shop. I just thought I'd bounce the behavior off the minds here on OSO for any insight they might have.

Thanks. Brad.

Guys,

We picked up the boat from Hilltop Saturday morning. They did exactly as I'd asked (mostly). They replaced the T-stat with the restrictor plate and back flushed the freshwater circuit, capturing the backflush (found nothing). They did NOT replace the seawater pump, saying they "ran out of time" before our pickup date. The boat is still in Burnside, so I wil probably call them and ask if they will retrieve it and do the seawater impeller before we return this coming weekend.

We put in at Conley Bottom and ran to the raft-up at Camp Earl Wallace on Cumberland. Boat ran fine. It warmed up to ~150° waiting for the wife to return from parking the truck and idling out of the NWZ. Then the temp worked its way up to 180°, running a fairly consistent 3500RPM, and stayed there for the duration of the run, with oil temp a little over 200°. Same thing going to Rowena, then same thing from Rowena back to Conley. It hovers right at 180°, even after the 4K RPM run, outrunning sunset back to Conley Saturday evening; oil temp peaked about 230-235° during this run. It does slightly spike to about 185° (closed cooling temp) when we settle in after a run, then hovers at that 180° mark for quite a while after. The steam slowly diminishes over some time idling, but never goes away (I expect some always).

I've got good output through the intercooler overboard. It takes longer than I'd think would be necessary to get water from the port exhaust tip, specifically, and we get what I would consider a lot of steam from that side when we settle back in after running a while. Part of me wants to think the closed cooling side is not circulating sufficiently, as that's how the temp climb seems to indicate, but the slow output through the exhaust seems to indicate low seawater pump output.

I know 180° is not really a problem, but it seems to be slowly running warmer and warmer over time, ever since getting the injectors fixed in late '22, and I'm afraid it's gonna run off a cliff when it's least convenient (when sh!t always does). Am I getting spooked over nothing, or should I be concerned. Is this just the new "normal", after getting the injectors fixed, given we are a mild supercharger on a stock 496 heat exchanger"? Even though this behavior didn't suddenly arise after getting the injector issue worked out....?

Thanks. Brad.

With the restrictor plate my testing shows it should run around 165 with a stock heat exchanger. This is also with an intercooler pulling water before the heat exchanger. If your seawater pump inspection doesn't have any results, I'd make sure they checked it for bravoitis.

87Mirage,

Just for reference, how much boost/HP are you finding that figure at? We are peaking at ~3lbs at WOT, and that 4K RPM run was still not into positive manifold pressure for us.

You're thinking it's not pulling enough water? Just enough to feed the intercooler, but not enough to sufficiently pull heat from the closed cooling side? This would make sense, since the port side has always run just a bit warmer than the starboard. The reduced water intake could be drawing that port side flow to near zero. We'll see what they say after changing the seawater impeller. This would also reduce the life of the impeller, correct?

I can definitely see the restrictor plate changing cooling behavior vs the T-stat, though. Especially while idling in the harbor, waiting for the wife. It's much slower coming up to temp and stops climbing at about 150° until we take off, whereas, before, it would heat up to about 165° fairly quickly.

My dumbazz put a hitch lock on the trailer, mostly to satisfy the wife, so they won't be able to tow it to their shop without cutting/breaking the lock off (I gave them permission, if they can do it without damaging the coupler). He said they'd work something out. Don't know if that is going to involve a traveling toolbox and doing it in our driveway or a hammer (it's a cast zinc Master brand hitch lock; easy to break). We'll see....

Thanks. Brad.

I believe it's common on a 496 port side exhaust to have less water output. Mine was like that when I first got it. Maybe a Procharger runs hotter, but my 496 with a Whipple doesn't exceed 160 after a run. I have the 120 stat recommended by Whipple. I'm at 140-145 at idle. You could be pulling air into the raw water cooling system. My boat had a transom fitting that went to the sea strainer so you could run it out of the water. I found the aluminum connector going into the strainer had corroded. I removed that flush line completely and put a stainless plug in the strainer bung. I took the hoses off the oil and fuel coolers and made sure I had no debris. I back-flushed. I took the ends off the heat exchanger, removed it and flushed it. I filled it with (I think) 50/50 coolant and distilled water and added two bottles of Redline Water Wetter, all as recommended by Whipple. I also upgraded to the $700 stainless Hardin impeller housing. You could have Bravo-itis or a hose clamp at the transom or one of the other water intake hoses that are not completely tight. My port side exhaust now seems to work as well as the starboard side. It may take a few seconds more on start up, but flow is similar and I do not have any steam. You may have to look at installing a transom pickup for your intercooler, if you're now feeding it off the raw water intake. To me, climbing temps indicates a worn impeller or housing. I would probably spend the money on the Hardin pump, I'm not a fan of the stock Merc pump. IMO, you have something going on. It could take a lot of time and effort to solve.

DonJuan,

It’s a brand new (OEM) housing, as of last March, so I don’t think it’s worn yet. The impeller is suspect, though. Working that angle.

Does the Hardin impeller housing pull/push more water?

This…?

I don’t have a strainer, so that’s out.

Thanks. Brad.

Guys,

Merc 496 raw water system

Can someone explain what’s where, as far as the general flow of water, in this?

Thanks. Brad.