Alarm sounds as if overheating-gctid826552

[Spyderweb2]

End of last season on last weekend out alarm sounded (Mercruiser 350 Mag closed cooling) after being up on plane a minute. Temp gauge read above normal (closer to 200 than 175). Boat was pulled as it was end of year and they found a bad impeller and changed it.

Relaunch boat in 2017 and boat works fine for several outings. 4th of July weekend it does it again. Different yard (My marina) takes apart impeller housing to see if it's scored or damaged. It is not. Since it's apart, they put in new impeller. They test drive the boat and temps read 170-175. I take boat out and temp definitely reads above 175, maybe 180 or 185, but no alarm. Service manager says run it. If alarm goes off this summer, bring it back in.

Boat then works fine all season until last week. Alarm goes off again. Temp gauge doesn't reach 200, but it's elevated. As before, dropping to idle, temp quickly drops to 175. And as before, It's fine running the boat slow, off plane, around 1300.

I typically run 3700-3800. Thought I'd try dropping tabs all the way, and running lower rpm's, around 2400 or so. Up for only a minute or so and alarms sounds again. This time I note temp gauge is hardly elevated. Reads about 180. After dropping to idle, temp gauge drops to 175.

Explain this to service manager. He sends 2 techs out, one reading a computer, and one checking engine temps with infrared gun. When alarm sounds for them and and engine goes into safety mode, temps with gun show 175-180 all over. Computer readout shows error codes but they are not familiar with them. They reach their contact at Mercruiser, and that tech has no idea what it is.

Please help!!

Paul

[builderdude]

Was the heat exchanger opened up to verify there is no blockage (pieces of old impeller) reducing cooling water flow? Also check for blockage at the inner transom shields water fitting (Bravoitis)

What were the codes? You need to find somebody that knows what the codes meant.

[Nauti_Mike]

"builderdude" post=826570 wrote:
Was the heat exchanger opened up to verify there is no blockage (pieces of old impeller) reducing cooling water flow? Also check for blockage at the inner transom shields water fitting (Bravoitis)

What were the codes? You need to find somebody that knows what the codes meant.

+1 vanes for old impeller may be blocking the system

+1 know issue to have the hose get blocked on the transom assy

+1 google the codes they read

[Spyderweb2]

Wouldn't the fact that infrared thermometer readings on engine reading normal when alarm goes off rule out any kind of blockage?

I will be talking to the service manager tomorrow about what the codes were.

The message left on my phone indicated the Mercruiser reps couldn't provide help on meaning of codes. That's disturbing.

[Nauti_Mike]

Is this a half or full closed cooling? Did they take reading on the exhaust manifolds and elbows? If so what did they read?

I would believe the IR reading but you also have the helm gauge and alarm saying it hot and these use different sendors.

[Centerline2]

"Spyderweb2" post=826579 wrote:
Wouldn't the fact that infrared thermometer readings on engine reading normal when alarm goes off rule out any kind of blockage?

Mercruiser reps couldn't provide help on meaning of codes. That's disturbing.

IS the engine reading normal?.... what temp thermostat do you have installed? if its a 160, then a180 reading is not normal.

fault codes are standard across the board. it doesnt matter if its a diesel or gas engine, an izuzu or a chevy, so whatever the codes are it shouldnt be hard to figure out unless the computer is throwing numbers that arent making sense to the code.... in which case I would question the computer itself, as it has the ability to change the timing and other settings on the motor that would cause overheating and potentially more severe problems. its an odd computer that will throw a "I have failed" code when they go bad, but they will commonly throw other codes...

[builderdude]

"Spyderweb2" post=826552 wrote:


Boat then works fine all season until last week. Alarm goes off again. Temp gauge doesn't reach 200, but it's elevated. As before, dropping to idle, temp quickly drops to 175. And as before, It's fine running the boat slow, off plane, around 1300.

I typically run 3700-3800. Thought I'd try dropping tabs all the way, and running lower rpm's, around 2400 or so. Up for only a minute or so and alarms sounds again. This time I note temp gauge is hardly elevated. Reads about 180. After dropping to idle, temp gauge drops to 175.

My upper helm gauge reads 175 after warm up all the time, my lower reads around 190-195. IR gun shows around 165 at the t stat housing and less everywhere els. All this to say many of the fellas have reported the gauges can be very inaccurate, including myself. On the temp returning to something you consider normal at idle or low rpm does indicate a potential restriction of cooling water. Not sayin its your issue but it won't cost anything to check those two areas off the list.

[Spyderweb2]

I believe the system is considered half closed cooling.

Talked to Service manager today. Temps were taken all over, manifold, elbows, t-stat housing. Highest they could get was 185. T-stat is 170. They could only get it to alarm and system to shut down at 42-4800 rpm. For me it sounded off at 3800. I don't know if system went in to guardian mode for me because I immediately throttled back when alarm sounded.

Most times with me temp gauge was elevated when alarm went off, perhaps 185-190. It's somewhat vague to read. The last time it did it for me alarm went off at about 175 according to Temp gauge, so that was inconsistent.

After talking to Merc rep they said computer actually did not show any error codes. What techs thought were error codes actually related to "garbage" codes that show when you unplug ECM and plug in computer. So Merc rep is not so sure boat is actually overheating either. They suspect something in wiring harness, or intermittent sensor problem.

Service manager has had 2 techs out on boat for 2 days now. Admits this is not their specialty. They have evolved into primarily Yamaha specialists. Said he would not charge me anything, and suggested I go to dealer (where I bought boat and now store each year) as they have much more experience in these engines.

Called dealer service manager and explained situation. He immediately sounded much more knowledgeable of these types of issues and has every confidence they can fix it. I will be taking it to him Thursday, which also becomes the end of my season as I planned to pull it next week anyways.

Thanks for your ideas. We'll see what happens next.

Paul

[Bad_Bay]

Had the same issue with a carbed 5 litre, so changed sensor still had alarm, so unplugged sensor. I always scan gauges anyway while operating boat. Now I have a 350 4 barrel in the same boat and probably same sensor as before, end of this season alarm goes off. So I unplug, and plug in sensor, and all is good. Dock neighbor has had his unplugged for years after trying 3 different sensors. You probably have a bad connection somewhere.

[Chief_Alen]

You say " bad impeller ".

In pieces or was the impeller in one piece.

Anyway ... Change out the t- stat make sure all the opening in the t- stat housing are open.

The pickup for the raw water tubes get clogged we call it bravoitis. Have that checked.

Elbows could be clogged, as well as the heat exchangers. Yea there is one for the power steering. Always overlooked in a overheat condition.