496 Mag Optimal Water Temp

[Nauti Behavior]

I have a 2007 Baja 23 Outlaw SST with 496 Mag. I took it out this past weekend for the first time of the season. Water was cold, but the air temp was hot (80-90 degrees).

After resolving a high temperature alarm issue I had with the closed cooling system apparently having air in it (pumped the water out and it was fine), I noticed throughout the day that the engine remained hotter than I remember in prior seasons.

At the lowest, the water temperature gauge read 160 degrees, but even at modest speeds and RPMS, the temp was up to 175-180 degrees when dropping speed for no-wake zones. This seems dangerously close to the 190 degree high temperature alarm zone. Is this normal, or should I be concerned about the impeller or water pump?

I only put 35-60 hours on per season, and replaced the impeller a season and a half ago. When I last replaced the impeller, it was just preventative maintenance, and the scoring wasn't bad.

Is this water temp. reading normal for the 496 Mag motor like I've been told, or should I consider replacing the impeller again... or worse yet, the entire water pump? If you suggest replacement, do you have any idea where I can get a new or refurb. water pump at the best price?

I appreciate your replies!

Happy boating,

Jason
Lino Lakes, MN

[gumbya55]

Check your thermostat, then check the impeller. I had the same issue, and after painfully going through everything, I found that the water pickup "tube" that goes through the transom from the outdrive to the water feed was either corroded or collapsed. My boat would only run hot when up on plane, at any throttle because it wasn't getting enough water.

Was told that the only way to fix is to pull outdrive, gimble, basically everything to replace...so instead I just put an external pickup and ran a new hose with a T to the water feed. Solved it instantly.

Hope that helps

[Redhook98]

I noticed mine sits at 162 or so when in normal operation. (Maybe 165 on the high side). When slowing down from running hard, it creeps up to 170 for a little while. Figured this was normal. My water pressure at the pump is 35 psi or so when running hard and 4.3 at idle so I know the impeller is good.

[blownhammer2000]

mine runs between 165-170 while running moderate to hard, creeps up to just below 180 when at idle, i'm running the hardin stainless pump

[Raylar]

Usually but not always when this happens on the 496's its a sign of raw water pump wear and impeller issues that cause lower than normal water pressure from the raw water pump. This inturn lowers the volume of water going thru the closed cooling system exchanger and the engine coolant temp gets hotter and has a harder time shedding heat. Try a scan tool readout of your water pressures at idle and at lets say 4000 plus rpms and see if they are in range. If its low, remove the raw water pump and repair or replace. If you replace I would still recommend the Hardin stainless water pump replacement, cheaper than Merc's brass pump and a much better unit.

Best Regards,
Ray @ Raylar

[Sydwayz]

www.mercruiserparts.com for a new pump, although your temps do not seem too bad.

How many hours? Have you ever changed the antifreeze? It's only good for 5-6 seasons.

[Nauti Behavior]

Thanks for all the great feedback.

@Sydwayz: No, I have never changed the antifreeze. It still looks good but, of course, that can be deceiving. It's probably a good idea to change it, anyways. The engine has about 140 hrs on it (2007 model year boat that I purchased used in 2009).

@Gumbya55: I had a drive failure last fall and the shop replaced virtually everything in the lower unit (gear set, clutch kit, U-joints, etc.).

@Raylar: I'll take a look at the Hardin stainless pump replacement. Am hoping not to spend an arm and a leg on maintenance this year, as I'm getting married in 10 days.

I appreciate any additional feedback. Thanks so much!

[Dave M]

The 496 I owned always ran around 170-175 regardless of air or water temps.

This has me wondering because I have a 525efi now and it seems to run around 150. That seems too low.

[Sydwayz]

If the antifreeze isn't bright pink, and has a "metallic" look to it, it's time for it to go. It silts up, which plugs the heat exchanger.

[blownhammer2000]

If the antifreeze isn't bright pink, and has a "metallic" look to it, it's time for it to go. It silts up, which plugs the heat exchanger.

whats the best way to drain the system, pretty sure mine has never been changed and i know i'm pushing it being an 06, 140 hrs and still has good color but really want to flush it out and refill, also whats the best coolant to get? i've heard good and bad when it comes to certain coolant types.... sorry for the highjack