Brad Christy

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.

underpsi68

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

Brad Christy

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.

Brad Christy

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.

87MirageIntruder

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.

Brad Christy

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.

87MirageIntruder

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!

Brad Christy

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.

87MirageIntruder

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.

Brad Christy

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 .

Thanks. Brad.