496HO T-stat
 

Guys,

So, I've noticed that the running temp in our boat has been slowly creeping up over this last season. It has always remained "under control", but it's getting high enough I think it's time to address it. The engine is a mechanically stock 496HO, with an M1 ProCharger and the Whipple stage 2 ECM flash. When Whipple sent the ECM back, they included a 140° T-stat. I called them and they said they recommend using it with the supposed higher output of the ECM flash, let alone the ProCharger. To the contrary, I've read a couple comments here on OSO that suggest sticking with the 160° T-stat, seemingly regardless of any power-adders. I've got an appointment with Hilltop Marine, initially to replace the cone clutch in the outdrive, but I think that issue has resolved itself, at least for the time being, via a shifter plate linkage adjustment, but I think I'm going to keep the appointment and have them do the T-stat. The question is which T-stat to have them install. Do I stick with stock or follow Whipple's recommendation? Anybody got a link for the 140° one, if that is the direction I decide to go?

Thanks. Brad.

Check the heat exchanger end plate gaskets. Known issue on the engines.

UnderPSI,

For the record, “I” ain’t doin’ sh!t. But I’m guessing Hilltop will know to check all known culprits.

I’m getting good flow from the intercooler overboard, if that means anything. I also had a new water pump, including impeller, put in last spring, so I’d assume the impeller is good, but I did run it for an extended period on the hose during the oil temp gauge project. I’m sure Hilltop will check/replace that, too, while they’ve got me bent over the counter.

Thanks. Brad.

Guys,

Quicksilver 8M0089715 Replacement Thermostat 140 Degree for Various MerCruiser Stern Drives

Amazon says I ordered one of these Jan of last year. I know, for a fact, I didn’t have it installed, but I’ll be damned if I can find it. No biggie. They’re cheap.

Is this the right part? It’s the right heat range, but I can’t tell if it’s the right one for the 496HO.

Thanks. Brad.

I've done a bunch of testing with Tstats etc on supercharged 496HOs. I would run the 140. You will find that even when running the 140, at cruise and higher rpms it will still run about the same temp as the higher temp stats. The factory cooling system can only do so much. Even when you run a 120 tstat on a supercharged 496 you will find it never gets below 140 anyways, even at idle and slow speeds. The heat exchanger just can't do any better. It will cruise around 170 still. In cases where a stock heat exchanger is used on a supercharged 496, I run a moroso restrictor plate (no tstat) with a 1" hole and have found it will drop the running temps by at least 10 degrees over running a stat. It will still idle at 140 too.

Personally I run a 5" aftermarket heat exchanger on my whippled 496, but that won't fit on a procharger system unfortunately.

87MirageIntruder,

Keep in mind we are only running 3lbs at WOT, and, even at a high cruise or 4K RPM, we are still just under zero manifold pressure. I get that we are turning more prop and running faster than the same boat with the same NA engine would, but I still struggle to call it a supercharged engine. That said...

Good info, and pretty much what I was assuming. I figured that, if Whipple saw fit to make the suggestion and include the T-stat, it was probably based on observed experience. The question is, do I have the right part linked above?

When you say "restrictor plate" do you mean as a substitute for the T-stat? Just an orifice plate where the T-stat would normally be placed? A 1" hole sounds like a lot, but I guess that's probably about what actually gets through the T-stat when it's wide open. Would this be appropriate for as mild as our boost is?

Thanks. Brad.

Yes the restrictor plate replaces the tstat. And you are correct a 1" hole is big, and is the largest one in the moroso kit (comes with 3 plates). If you look at the tstats they have 3 small holes to flow water, and this must be why the 1" restrictor plate works on a 496 cooling system. Meaning for this specific application, its the flow capacity of the tstat that is the limiting factor on cooling, not the heat exchanger itself. If you run a 1" restrictor plate, you'll run about 10-15 degrees cooler than with a tstat of any temp range. I hope I explained that good.

As an example, I just built a 496HO with a whipple for a friend. It has stock heads and a stock heat exchanger. I tried the 120 tstat then the 1" plate. With the plate it idled a few degrees cooler, and at cruise it was 10-15 degrees cooler than the 120 stat. I have a friend in Ohio that has built a few of these 496s also and he has found the same results. I was cautious at first with the concept of running a plate as old school teachings were to never remove a tstat but in the case of a 496 platform it actually works. I wouldn't do it to a completely stock one though, as they run forever if you leave them alone!

https://cimg5.ibsrv.net/gimg/www.off...64de588ed2.jpg

87MirageIntruder,

To be clear.... You're recommending a 1" restrictor plate instead of a T-stat for MY application: A mechanically stock 496HO with an M1 ProCharger and Whipple's stage 2 ECM flash?

It is my plan to take the boat to Hilltop Marine, in Bronston, KY (Lake Cumberland) to replace the T-stat, but I will go this route if it the way to go.

Thanks. Brad.

If it were mine and I had your mods, I would have hilltop check the transom assy for bravoitis, seawater pump, oil cooler on the port side for restrictions, and open the heat exchanger end caps to inspect/clean. Then you know you don't have a flow restriction or pump issue. And yes if it were me I would run a 1" restrictor plate instead of a stat. They still idle at a high enough temp for the engine to get out of warm up mode, and they run a little cooler which is important on a boosted engine with brittle cast pistons as the 496 has.

87MirageIntruder,

Roger that. All of it. I'll probably just have them do the stuff directly related/adjacent to the heat exchanger and T-stat, unless they determine through divination that some of the other things you've mentioned are contributing to the issue. While I don't want them having to go back and redo stuff they've already done, I also don't want them to have the boat longer than a period of time that resides in a planned gap in our schedule, if you follow..... I get the feeling some of that stuff might cause delays that could be put off until after the water cools too much to use.

What, exactly, it "Bravoitis"? Just in case hilltop is unfamiliar with the term, I need to be able to speak their language. They are a very good shop, with a really good reputation, but they don't do any kind of performance work; just repairs, routine maintenance, winterizing, etc. A lot of the shops in the area won't even touch a "hot rod" boat (their term), which I'm sure they would consider ours to be. I don't think Hilltop would be interested in any actual performance upgrade work, but they'll work on mine; I don't think it scares them so much :D.

Thanks. Brad.

Bravoitis is when the intake water hose going into the transom assy collapses from corrosion etc. It happens more in saltwater boats but does happen in freshwater too depending on the water it boats in. This is a common problem. Over time the engine will run hotter and hotter as it closes up. Mercury has now redesigned the water hose, so when you replace it with OEM parts it has a plastic tube going through the transom instead of the rubber hose.

https://cimg2.ibsrv.net/gimg/www.off...6afac7c376.jpg

You boat Cumberland… have hilltop clear the oil cooler and the heat exchanger. A solid backflush and removing the output from the sea pump will likely resolve the problem.

I know the lake and problem well.

Sunny32SSR,

Honestly, if it’s coming from any lake, it is from Caesar Creek in Ohio. I’ve been boating on Cumberland my entire life and never heard of a debris issue. Cumberland is, by far, the cleaner of the lakes I boat on.

Thanks. Brad.

If you choose not to run a restrictor plate do use a high flow t-stat. Maybe a 120 or 140 and drill an extra 3/16 hole in it opposite one another. They look like this and come in 120 thru 180
I agree with the 120 or 140, it will still run warm enough and likely run close to same at WOT. Double back and check with your blower supplier. Nickerson recommended a 120 high flow on my B&M 250 setup. When blower was removed I went to a 140.

Has anyone seen the 140 in this version available anywhere? I dug mine out of my parts drawer where it lived for years, not sure where I got it.

Do your drives have low water pickups?

Sunny32SR,
https://cimg3.ibsrv.net/gimg/www.off...5276a82e5c.jpg

Thanks. Brad.

Put it back together with the 140°F that is recommended. I assume the Whipple thermostat is a high-flow version. Do not run the Amazon version and get the high-flow from CP Performance.
https://www.cpperformance.com/c-123-thermostats.aspx

Rookie,

Appreciate the input, but I've already ordered the restrictor plate kit and will be calling Hilltop momentarily to make arrangements for the end of the month.

Thanks. Brad.

Not to hi-jack this thread, but I never knew about the 1" plate. My Whipple 496 has a 120 tstat. During the middle of the summer, it runs about 145-150 degrees running. When I come into a 5 zone, it goes up to maybe 160. I have forged pistons. Any benefits to switching to a plate on my setup?

No

Aside from the fact he likely needs a 140 and not the 160 on Amz.-

When you say Amazon version are you referring to the Stewart Warner High Flow I linked, this is actually a Robert Shaw T-stat marketed by SW? Just trying to determine if there is a functional difference or known quality issue with the Stewart Warner (Robert Shaw) T-stat. It is Brass construction. Do we know anything about who manufactures or where the CP T-stat comes from? As I am fresh water I see it as a one in maybe 10 year purchase. I ran my 120 High Flow (unknown brand, bought in 2001) for 10 or 12 years and it still worked same as new. I am just looking to source a 160 high flow for a different boat and or perhaps a 140 depending upon some further testing. Just easier to for me to buy from Amz, Prime, free shipping etc. I am going out on a limb I suspect any Brass one we come across is likely made in the same place.

DonJuan,

I'm not the expert, and I have no empirical evidence, but here are my thoughts....

I guess it depends on whether you have closed cooling or not. From all the reading I can find and contemplating on it, this seems to make all the difference. If you have fresh water cooling, I can definitely see the need for a T-stat. You really don't want pockets of 85° water coursing through your block and heads. But with closed cooling, the coolant is going to warm up regardless, and it will not have the occasional pocket of much cooler water. It may take a bit longer to get to temp, but not significantly. The end result will be more cooling capacity via higher flow than a T-stat will allow.

We're gonna find out. :food-smiley-007:

Thanks. Brad.

@Brad. Yes, stock heat exchanger. 87Mirage thought my temps were good with the 120 tstat. But if a plate cools it down another 5-10 degrees, maybe I should try the plate. More flow seems better. As far as warm up, I have ten minutes in the 5 zone to fast water.

The Amazon did not have the spring loaded bottom plate like the 496 does. I have no idea if necessary or not. I also run the SW High Flow T-stats with no issues.

Rookie,

The one I linked is a Quicksilver, from the Quicksilver store. What's the difference between this one and what you're talking about?

Thanks. Brad.

Never assume (guess) . Sincevyour going in for a cooling issue, Tell’m you want these replaced anyways. :thumbs

SB,

Agreed, and that would be the plan. It's been the better part of two seasons, anyway, so no money lost/wasted. I am just trusting them to not let me forget. ;)

Thanks. Brad.

My screen name is SB.
Most of us , but not all, choose not to use an actual name.
Thanks.

SB,

Heard and corrected. :ernaehrung004:

Apologies.

Thanks. Brad.

Post #7 is the 496 thermostat.

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.