Rage

The base engine is a Merc 496HO but with Dana Marine EX2000 Flow Torque Exhaust Manifolds. Engine just rebuilt. Was 625 hp before now more though idle should be no change. Before on lake exhaust would stabilize at ~ 120F - 130F at 730 rpm idle/cruising and sea water pressure ~2.6 psi. Now on the garden hose in the driveway new engine exhaust manifolds keep getting hotter and hotter. In 6 min port exhaust is 180F, starboard is 138F and both still climbing with idle at 830 rpm and sea water pressure ~2.0 - 2.1 psi. I repeated test after replacing water pump impeller and same result except pump pressure now 1.8-1.9 psi at 830 rpm. Water is supplied to lower unit with U spring-rubber suction cup type adapter at mid water pickup. My X drive has the lower pick ups as well which are taped shut Hose water pressure is un regulated city feed so high @ ~ 80 psi. with engine running plenty of water still flowing past the rubber cups.

I have a lot of run time data history from on lake but zero in drive.

Has anyone actually experienced anything similar in drive vs on lake exhaust temp difference?

JerseyOutlaw

Always had cooling issues when I had my 496. I solved it with a Hardin Marine transom mounted water pickup to a Gil sea strainer to the sea pump. Sold the HO for bigger power.

Rage

Can you elaborate on what type of cooling issues you had/

Dave M

Never had cooling issues with the 496HO I had. The port exhaust temp was always 10* hotter than the starbd side. I'd concentrate on what the water psi is on the water, not the hose. Too many variables there. 2.6 psi idling in the water sounds low. I don't remember what my 496 was at but my 525efi is between 3-4 psi at idle.

Check your water pump housing, they get grooved and don't work as well as new. Bad part is they are very pricey. I like the plastic housings that you replace with the impellor.

BUP

iTrader: (9)

do you still have the check valves installed the is the OEM stock set up ?

BUP

iTrader: (9)

look at part number 28 and 29 do you have these ? Not sure cause your app is from stock and have the Dana's but that does not mean you did not use the connection and check valve / check balls however you want to call them.

http://www.boats.net/parts/search/Me...ser/parts.html

Ryan00TJ

iTrader: (8)

I agree. My port runs 10-15* warmer than stbd. Manifolds run warmer on the garden hose vs lake.
It comes down to the 3/4 garden hose cannot supply the gpm of what the seawater pump can flow, causing warmer temps on the hose. I would water test and go from there before anything else.

BUP, The only purpose I see for those check valves is to keep water in the manifolds when not running. Am I wrong?

02RedWS6TA

My 496 is the same way. Hotter on the hose than in the water and hotter on one side vs the other. I hate running it on the hose.

BUP

iTrader: (9)

the check balls or check valves for all MPI using OEM cool fuels are very important.

Why because after you shut the engine down and the cooling water internally and engine heat soak - the check balls keep that heat soaked water from draining back down in the cool fuel system causing (vapor lock) fuel boiling off in the cool fuel cell / fuel pump(s) - OEM Gen II and Gen III cool fuel systems.

Now the check balls or check valves can get stuck or break apart or get restrictions causing cooling problems - people who do not winterize their engines properly freeze break them and have a heavy water leak in the spring.

People who have taken them out of the system in my area many had to get towed in on the very hot summer days with warm lake water after engine shut down to hang out in the water . Upon restart of the engine - the fuel boiled away in the cool system hence the engine would NOT restart for them. I have verified this many of times in July and Aug in Texas with owners who have removed the check balls / valves for varies reasons. FYI.

BUP

iTrader: (9)

On marine apps you are going to get one side of the manifolds / risers hotter than the other. the 496 is the worst. Take a look at where the t stat is mounted on the 496. I have seen up to 18 degrees difference.

Marine engines in general have unequal water flow and unequal water flow distances is some of the reasons for one side hotter than the other.