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.

[abl1111]

Where did you get the manual for $75 ? I thought it was like $150 for just the engine manual ( we are talking about the Mercruiser service manual, right ? )

<< 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.... >>

That is very nice of you. We don't even know each other and you're willing to help out. That in itself means a lot.

Thank you.

When I re-did my boat, I opted not to get the Smart gauge package because:
a) I was broke and it was expensive, and
b) I thought that analog was simple and accurate.

Today, I borrowed from my mechanic the Mercury Diagnostic Computer that plugs right into my boat. Talk about a nice toy ( sounds like what the SmartGauge would do ).

According to the diagnostics, the boat temp is on the money - 163-165 degrees, even at WOT. My gauge must be bad - even the replacement gauge ! I borrowed a buddies spare temp gauge also, a Faria brand, and hooked it up - shows me at 175 degrees from the sending unit. Infrared thermometer showed same at sending unit. At thermostat, 1.5" lower, it was 165-167 degrees.

That sounds OK to me.

I will wait for the raw water pump R/R till the Fall pullout.

I 'think' this case is closed. Just goes to show you, no matter how careful you are, sometimes it's something stupid.

I am going to look into eBay/online for a Smart gauge.. What do you see them for ? And, do you like having one ?
Is there a sending unit that is needed - is it an EZ install ?

Lastly, thanks again for being a good guy.

Alan

[1bayouboy]

Go to www.go-fast.com and do the parts search->search with pictures-> and keep selecting your engine type, model, serial number range. When you get to the main parts breakout there's a selection for service/support material. The main list stays in the upper left corner, the exploded diagram at the top of the page, and the parts breakout and cost at the bottom window. The service manual for a 350Mag Horizon was listed at $67.85 and change. The sternleg manual was about the same.

I started with analog gauges since those were in the boat I bought and it was simple to plug in to the big round connector on the back of the engine. The I bought a monitor for the fuel use info. Then I had a buddy give me a Smartsystem Tach so I went out and got a Smartsystem Speedo and the link gauge for temp, oil and batt. Getting a tank gauga and digital trim gauge was more trouble than I though it was worth as it required new tank sender and trim switches. The guages are awesome and easy to connect.

The main thing is to get the right cables. The cables can either connect directly to an end device like the Monitor or the engine, or to a Hub. With a single engine you need the terminated cable and it just connects to a connector on the back of the engine near the analog connector. That cable goes forward and connects into the back of the Monitor Guage if it's terminated on that end, or you can connect the cable into a Hub, and then use a different short cable to go to the guage. For multiple engine you can have a Hub on each end of the boat and connect all the engines to the one in the back, and all the guages to the one in the front. So the layout is really easy....you just have to kow what cables. With the Speedo/Tach they each connect to the hub and then the oil, batt and temp gauge daisy chain with a two wire connector. Talk about eliminating wiring.

And while I haven't met you I've seen you post on the board many times so I kind of know you...

[1bayouboy]

Here's a link for serial numbers 0M600000 THRU 0W059999
for the Horizon FWC packages....

Service and support material

90-864260001 SERVICE MANUAL, Service 90-864260 Component Of Long Block Assembly-Long Block Part Numbers Listed On Service And Support Material Page $67.85


And you can use the part numbers to do Look ups by part number too.

[gss036]

What kind of risers do you have? Most of the guys I know have to replace them about every 5 years as the rust out. One friend who also has the 350 Chev in his 24ft Bayliner got tired of changing them and ordered a set of stainless steel risers and they work good and really look good on the engine.