496 HO running hot
 

Just added a harden marine water pump housing and impeller,thermostat was replaced last summer. Engine is heating up tp 170 @ 4000 rpms, port manifold is 146 and starboard is 134 degrees. On the way back to the dock the engine started to miss. Original 2004 mercruiser exhaust manifolds. The boat was used in saltwater by the previous owner. Fresher water use now. Any thoughts....manifolds leaking?

Was it running hot before the pump change? Check the water hose where it bolts to the transom, its two 11mm bolts.

It was not over heating, but it was running warmer (165) and took a little longer to cool off after a good run.

I'm not sure how long the water circulating pumps last. Since it started missing I'm leaning toward faulty exhaust manifolds ( 10 years old- salt water use). I plan to check the plugs and pull the manifolds - replace with cmi etop headers. The missing has me concerned.

I have a Rinda scan tool,erased all faults and ran a system check. No faults other than the normal ones that I get.

I see on smartcraft gauges these motors run 164 to 172 all the time even new. Anyways always one side exhaust manifold is warmer than the other side because of uneven water flow. IMO if you stayed steady eddie at 170 degrees in all running conditions you are fine but of course running closer to the 160 to 165 is always better. If this motor sets a warning horn and or goes into guardian mode then most likely you are overheating.

Ok, I guess I should have seen if it would have gotten hot enough to go into guardian mode. I also got concerned when the engine started missing.it will be interesting to examine the plugs tomorrow and test the coils with the Rinda.

How old is the antifreeze? Is it still pink or is it starting to get grey/metallic? 6-7 seasons tops on antifreeze in any of these closed cooling motors. It's starting to silt up when it gets dark, and will not flow well or cool the motor.

Is this a new temperature you are hitting? That doesn't seem too high to me. Does your Rinda say you have plenty of water pressure?

Yes, definitely hotter than normal. Last year I had similar issues and you assisted me. Antifreeze, thermostat and flushed heat exchanger within the past year. All new sensors. New Hardin marine pump and impeller. I should have noticed the water pressure but was to focused on the engine and exhaust manifold temps.

Agree with Brian here as well. The anit freeze is a Dex-cool extended life mix 50 / 50 from Mercruiser. You can buy Dex-cool use distilled water50 / 50 mix if you change your anti freeze . Tap water has minerals in it and can over time leave deposits in the cooling system. Anyways OEM Merc spec on the anti freeze is 5 years or 500 hours which ever comes first. We change it at 5 years or 400 hours whichever comes first. If you are not using extended life anti freeze then Merc spec is 200 hours or 2 years which ever come first.

Water circ pump and or t-stat can play a role here for higher temps especially t-stat with very old anti freeze still used in the cooling system. Old anti freeze loses it corrosion protection properties over time thru heating & cooling cycles along with oxidation. Also old anti freeze persay not to get into a story book write up here adds surface tension in its flow patterns thru the cooling system. .

If you have smartcraft gauges you can watch your water pressure running. I leave water pressure displayed on my gauge all the time to monitor any changes with it. .

Is there a way to determine if the exhaust manifolds are bad or leaking? Any good advice to breaking the bolts loose on the manifolds? Since they've been on for 10 years I would imagine this could be the biggest challenge.

CRC freeze off or the new Loctite formula for frozen fasteners but before you apply the CRC might want to heat the bolts with a hair dryer on high setting. Also old machinist trick is transmission fluid & acetone mix to free up nuts / bolts / fasteners

Separated the exhaust elbow from the stock exhaust manifolds. There appears to be no signs of water...just looked like dark exhaust chambers. Is there anything I should look for or should I pull the entire exhaust manifold?

Turbulators looked ok.

Checked all the spark plugs, all of them looked great. The only issue was the four on the starboard side were not tight at all. The four on the port side were tight.

Are there any shops that will test and clean the manifolds?

You may also want to check the transom assembly. I saw a 496 ho similar situation with salt. It was 1/2 closed off due to corrosion where the engine pulled lake water through the transom assembly. Took a while to find and didn't fully overheat just running warmer than it should

x2

I'm getting some water in the bilge, would a bad actuator cause the engine to run hot? Since I have the elbows off I may go ahead and replace the circulating pump. I'm sure it's the original.

Yes, that could be a culprit too. When they go bad, they usually only leak over 3000 rpm.

I guess it's time to purchase a couple rebuild kits. The exhaust manifolds and elbows look good, I can't see any corrosion in the passages.

Looks like the starboard actuator connects to the water pump. Do you have to pull the seawater pump to rebuild the actuator?

Did someone say there are mercruiser rebuild kits for the air actuators? The local mercruiser dealer says they do not exist.

There used to be, but I haven't looked for such.

Member "BUP" would know for sure.

Will add, make sure you are not leaking water at your blue plastic drain plugs as the O-rings might be missing on the blue plastic drain plugs. Also I have seen people strip the threads on the blue plastic water drain plugs that cause a leak. Anyways maybe or hopefully a simple fix for you but who knows.

Currently you can buy the fittings to your actuator(s) They are your grey & orange fittings that can be 90's or straight - you can buy either. You can buy the blue plastic drain plugs and the O-rings that go with them for the water drains manually. You can buy the green and grey hoses that connects to your actuators fittings (90's or straight fittings) Next you can buy the actuator assembly water drains starboard and port - cost is 301 for starboard and 300 for port retail.

I would see if you can figure out what actually and where your leak is coming from as hopefully the fittings and or blue plastic drain plugs & O-rings could fix your leak instead of buying the actuator(s). Also with the starboard actuator it will be determine by engine serial #. just in case that's what you need to buy. I hate to be a broken record but engine serial # dictates parts, installs and service procedures on all OEM factory marine engines in stock apps.

I can give you any part #'s if needed but will need your engine serial # for the correct ones if you need actuators and or fittings and what type of fittings 90's or straight.

Thanks for the replies. The cold fuel cooler makes it really difficult to see the actuator. The blue plastic drain plugs are new and I confirmed they are not cross threaded. I back flushed yesterday day and noticed no debris. The manifolds and elbows look good. I'm going to put them back together and order a water circulating pump and a T so I can run it at my house. The harden marine seawater pump is brand new. The serial # is 0w064103 which should be the 496 MAG HO 425 hp.

Ok you have the first Gen for the starboard actuator water drain assembly. Merc part # is 863716A2 and retails for 301 and the port actuator is the same through out Merc part 863717A2 just in case and the price retail is close to 300 bucks.
I had to reword my post above about the hoses as they will not cause a water leak. I was posting the parts that anyone can still buy as individual parts if needed.

X100 !!! I have found 2 of these in fresh water boats !

Pretty expensive! I'll do some checking first. Since the Hardin pump was just installed I'm going to check it for leaks .
Thanks!

Can the actuator springs be replaced or ordered? Read some other posts that said the springs can get soft. I have two days to try and figure this out.

Just pull the actuator assembly out and replace it with a piece of 1 &1/4 pipe for the time being. It will be fine. (If I remember correctly, it's 1 1/4 OD pipe.)
One of mine went bad before I bought my boat, and original owner lived in Arizona; no need to winterize so he just pulled the actuator and stuck a pipe in there. It worked great for months.

We did the same on another 496HO when we were on a trip through the Keys a few winters back. $10 taxi ride to the hardware store; 2 new hose clamps, and the boat made it home no problem.