Mercruiser question - Temperature problem

[abl1111]

I have a 2003, 350 freshwater cooled motor w/ 280 hours - still under extended warranty. Bravo 3 drive and cooled via SouthBay strainer.

Temp gauge went to HIGH a few weeks back. Stopped motor, called mechanic - he said if no alarm - no problem. Motor runs fine. I run usually at 3200 rpm's...

Coolant was 3/4 gal low. Oil, was 3/4 quart low. Added both - and changed the temp sending unit and the gauge.

Sometimes, she will run perfectly but at some point within 30 minutes, she will read High.

Used infrared at thermostat/sending unit - at 165'ish degrees @ idle. Bypassed harness via a jumper from sender to gauge - still HIGH.

Ran cold hose water over sending unit, temp. gauge lowered a bit from High - then rose when water removed.

I'm all over the place with troubleshooting; bad thermostat, check compression, head gasket, pressure test cooling system, manifold blockage, etc..

What are your thoughts ? Thx

[oldfielder]

Did you pull the end caps off of the exchanger and look for crap in there. It sounds like there may be stuff in there causing a restriction and as your demand increases perhaps the h2o flow just isn't there. when was the last check of the raw water pumps impeller?
What about a gauge that gives you temp instead of high/low/just right?
165 sounds like where it should be.
Also, when you jumped out the harness, did you also jump out the ground? If that wire has some corrosion, could the extra resistance be messing with the sensitivity of the gauge.

[1bayouboy]

Definitely check the raw water pump impeller. I thought it was going to be a real PIA, but after removing the alternator and the cool fuel module, getting the pump off was easy. I had a couple of pieces of impeller missing so I had to go look for it.

You can take you engine serial number to www.-go-fast.com and do a parts earch with pictures to get exploded diagrams of everything. The raw water path on my 2006 model was from the pump through the power steering fluid cooler on the back of the engine then to the heat exchanger and out each end of the heat exchanger into the elbows.

I'm assuming there's good raw water flow out the exhaust??? The issue could be the circulation of the fluid inside the block.

[castalot]

i had the same motor pull the end caps off the heat exchanger and run a wire or air through the tubes should fix the problem!!

[abl1111]

" Did you pull the end caps off of the exchanger and look for crap in there. "

- I pulled off one side - the other side is a little more work to remove because the oil filter bracket must be removed first. The one side was clean - at least the end was - can the small holes can get clogged within ?

" When was the last check of the raw water pumps impeller? "

- In four years - not once ! I think I am going to attack that immediately. Seems like a b*tch of a job because it is really tight !

" i had the same motor pull the end caps off the heat exchanger and run a wire or air through the tubes should fix the problem!! "

- Even with a Southbay, thru-hull strainer stuff can get stuck in there ??

" You can take you engine serial number to www.-go-fast.com and do a parts earch with pictures to get exploded diagrams of everything. The raw water path on my 2006 model was from the pump through the power steering fluid cooler on the back of the engine then to the heat exchanger and out each end of the heat exchanger into the elbows. "

- I'll check that site. I really need to buy a Mercruiser shop manual ! I feel blind without clear directions.

" I'm assuming there's good raw water flow out the exhaust??? "

- Boat's in water - I had assumed I was getting good flow ( now, nothing is off the table ) - how do you check w/ her in the water ?

" The issue could be the circulation of the fluid inside the block "

- No idea

" What about a gauge that gives you temp instead of high/low/just right? "

- Mercruiser does not make it - mechanic wants me to get the SmartCraft stuff. I like analog - it's simple.

" Also, when you jumped out the harness, did you also jump out the ground? "

- I bypassed positive, negative and sender/harness wires. Still HOT.

This is my first foray into an i/o. Grew up with and watched my Dad wrestle w/ them for years - I swore I would NEVER own one. I have had OB's on every boat but my 23' Tsunami. This boat had twin i/o's and I converted her to one. She handles great. I am very under-educated with how the 'flow' of cooling happens.

I am mechanical, but have no experience with the i/o ( and no shop manual ). Looks like I'm on a fastrack right now !

[1bayouboy]

The manual was the best $75 I ever spent...I got both the Engine and the drive leg manuals. I have a smartcraft monitor and cable I think will fit on your engine. I'm willing to let you borrow it.......if you like it you can get one....look on ebay for deals. On my engine it attaches to the CAN cable on the back of the engine. It will give you hours, fuel flow and usage, engine temp, oil pressure, and raw water side water pressure.