"Im new to the site but have looked on here before for ans and opinions" I have a 99 Baja H2X with a 454 MAG MPI, i bought it about 3 months ago. I have owned Outboards for yrs and this is my first I/O. The other day I ran from Orange Tx to Lake Charle La, which is an hour boat ride. On the way there my Water Temp Gauge showed around 135*, ran great. Stopped at a local sandbar/casino/bar. in Lake Charles, hung out there for a few hours. Went to leave and drove about 1/2 mile and i noticed my water temp gauge had climbed to 180 and was still creeping up. I shut down the boat and check in the eng compartment looking for anything out of the ordinary. then i got in the water and had my wife start the boat while I held my hand under LWP to see if it was sucking. it wasnt right off the bat and I figured while at the sandbar I must have sucked up sand or trash. I was able to feel the pump start pumping the water temp went down to 150* but would rise when adding throttle, but go down after idling back down. After getting home I backflushed the cooling system from the T housing to output on the sea water pump, did not find alot of trash. BTW I did not drive the boat after the over heating issue, trailered it home. I ran the boat on the water hose and the temp would rise to 160* as before on the hose the temp wouldnt get to 150*. I have noticed now the STRBD exhaust elbow is hotter than the Port and noticed steam coming from STRBD and not PORT. I ran the boat in the water today to see if it would over heat, for the first 20 mins I would get on plain and shut down, I did this about 5-6 times with not WOT, just enough to get on plain. The temp stayed at 135*. Then I took it for a cruise at 3500 rpms. I noticed the water temp creeping to 165* but never getting to 180* and at idle it would go back to 135*. and Im sorry about writing a book here, but just wanted to tell the story about what had happened and what i have done so far. My question is should i be worried about the exhaust elbow and the steam from the STRBD side and is there anything that i might want to check? I know the Riser and elbow are an issue to be checked for blockage also. Just looking for a little guidance in trouble shooting if there is an issue

Thanks
Matt

Just to note that i changed the Sea Water pump a few days before, the old pump was still in good shape, changed because i had it off and had a new kit to install for the season

It should run at 160-170* on the gauge if it has the correct 160* T-stat.
I does sound like you sucked up some sand though and it may have mostly cleared out.
Pull the water hoses off your oil cooler and flush through it and also pull the block drains to check for sand.

ok thanks
is ok to open bleeds on block and flush through the eng block with eng not running of course

i know that would require pulling the t stat also to allow water passed it

I have run my engines(at idle) with the block drains pulled with no problems.

Impeller housing scared and wear plate most likely if you sucked up lake bottom. Possible will have to change that. Also possible abraided impeller tips if you sucked up a good portion of sand / lake bottom.

First of all how bad or good was the old housing as you just mentioned impeller only. or Did you change the black housing and wear plate and new O rings when you changed the impeller ? I never install impeller only for that app. The black plastic housing are very easily prone for wear groves mostly within 2 years time even without sucking up debris.

Also is the housing leaking water - Many people over tighten the housing bolts / nuts - cracking it ? Also they are spec ONLY at 10 ft lbs and in a 3 pass star tightening pattern.

Next pull t stat housing and check for debris and make sure T stat is working and clean - if its older than 10 years old I would change anyways. Expect to break the plastic insert that holds the t stat in place when pulling it out.

Next - Water jackets plugged in the exhaust manifolds and or risers ????

Next you can stick metal rods thru front to back of the oil cooler with hoses off. I have seen many times lake bottom pebbles completely stuck in the honey combs.

Do you have a sea strainer ?

Im running my 454 mark iv with a 180 degree thermostat--is that too hot?

Stock Merc carbed are 140* and EFI black engines are 160*
I would run 160* max.

just saying wrong info about all CARB engines. all Mercruiser and Volvo Pentas in late 1995 went to 160 degree t stat for CARB engines as well. Anything back of those years engine side for carb engines is 140 degree T stat.

ACTUALLY it is all determine by engine serial number.as to what parts are installed including which degree T stat.should be installed. Mark IV is older and takes a 140 degree T stat.

To prove my point for the na sayers about the carb 454 - check out link below for a carb engine serial number run and look at the years of the engine (1992 thru 1996 ). . The T stat is 160 degree in diagram number 5 for that certain serial number runs inwhich were around the year of late 1995

YEAR MODEL means nothing - to which parts and procedures along with set ups for OEM stock marine engines have installed. I have posted this a 1000 times. Know your engine serial numbers - it is very important for the correct parts installed and service procedures.

Alot of MPI engines with closed cooling are 170 degree T stats. Raw water cooled MPI engines use a 160 degree except if I recall correctly the HP 500 EFI inwhich is 140 degree T stat.

http://www.marineengine.com/parts/me...-n-0f305000-up

And the serial numbers and years showing its a carb engine

http://www.marineengine.com/parts/me...rburetor-weber