Water temp at zero, goes up after shutdown

Chrisvr6

Still having this issue on my 93 carbed 454 magnum. Did an impeller/thermostat/proper gasket change and now the temp is at zero when running. Now, when i shut down, the temp then goes up to 180°. And it does smell like its running rich. 

MarkB

Thermostat stuck open?

Chrisvr6

Put in a new one last night. Nothing. 

Chrisvr6

I see water in there when i pull the thermostat. It would overheat if there was blockage. No? 

212rowboat

Check the posts in the back of the gauge.  see if they're reversed. 

Chrisvr6

It never was overheating. Its overcooling. I can get the temp to come up a little if i shut the engine hatch and just crack the water spigot a little bit while running on muffs. In the lake it stays at zero. 

212rowboat

As far as rich, I'd wager your choke is stuck... They think such behavior is the height of hilarity, and do it often... The only long term fix is to either install manual choke, or.... Efi... 

frodo13056

Any chance the thermostat was installed upside down? I seem to recall that the thermostat housing had 2 hoses that go into it from the sides and that there were springs and balls (acting like a check valve) arrangement in that housing - I did a quick search on the internet and found a diagram that shows the spring / ball arrangement that I remember. Is it possible one of those is missing / malfunctioning?
http://www.marineengine.com/parts/mercury_marine_parts/static/img/CRUISER/824390.92/27.gif
Item 4/5/6 is the assembly. I'm not really sure how that whole cooling assembly is supposed to work, but if the ball/spring assembly is stuck open or missing, you may be getting reverse flow, short circuiting of water, etc.

212rowboat

The temp sender is stuck in the water jacket and is independent of the 'stat... If it's a single post style, it's tired and needs swapping... If it is a two wire, I'd be looking at its ground, which is required to be very solid for proper readings. 

Chrisvr6

Hmmm. Tired sensor? I just may change it. The balls and springs i changed already. 

Chrisvr6

Wondering now if all that Vaseline i used on the impeller during install didn't coat the sensor somehow to cause it to not read. 

Chrisvr6

I do have a meter. 

Chrisvr6

Well why would the needle on gauge creep up to the correct temp after i shut down though? That's what's weird. Start it back up, and it cools back down to zero. 

Chrisvr6

Yes, when i turn the key off to kill motor then turn key back to on position before cranking the temp goes slowly up to correct temp like the water in housing is not moving so ots building up to the heat of the engine. I assume i have the alarm on the water in the housing sinnce there are two sensors in there. 

Chrisvr6

Had to take the boat back to storage last night. I'll try what you suggest this weekend. 

MarkB

Ground issue?  If it's hot and off, the temperature moves slowly to 180F right.  When it's at 180F and you turn the engine back on, how quickly does the needle move back to 0F?

Chrisvr6

It creeps back down as the new cold water comes flowing through. 

MarkB

So it sounds like it is moving in the right direction, it just isn't in the right range. Is the temp gauge compatible with the sensor, that being is the ohm range aligned? 

Chrisvr6

Its raw water. It was fine before i changed the impeller and thermostat. Its like the raw water pump is too powerful or something.

Black_Diamond

It's not the raw water pump being too powerful, it can only move so much water and it's the same design for several Mercury engines.  I bet you have a ground issue.

212rowboat

You'd hit at least a benjii without a stat at all... 

Chrisvr6

Hmmm, good point drewactual. I think it starts at 100. It even sits below that when running. 

Chrisvr6

If it were a ground issue it wouldn't come up on the gauge at all. No? 

Black_Diamond

It's not wired backwards for some odd reason is it?

212rowboat

I once ran a 408 with an air gap manifold on it... the temp sender housing had a bubble in it... I didn't get rid of it until I pulled the sender and ran the engine, and screwed it in with the engine running.... maybe, just maybe you're seeing something similar? 

Chrisvr6

That sender sits in water all the time no? I think I'll try that drew. Thanks. 

MarkB

Chris, if you shut engine off, power is cut, so ground doesn't matter anymore. 

212rowboat

markbellino said:

Chris, if you shut engine off, power is cut, so ground doesn't matter anymore. 

Sensors still report on a thunderbolt so long as key is on. 

MarkB

Yes, when I mean off, I mean the key is in the off position. 

JoeStang

I had pebbles stuck in my tstat last year and I thought the gauge was bad as it never came up to temp. My engine would absolutely not get above 100* at any point, and it was running rich enough to dilute the oil with unburnt gas. Swapping the stat is simple and cheap, and I'd get a new sensor too. Make sure to get the right gasket, as I know mine has a metal ring built-in I believe for grounding.

 They actually thought the sensor was bad so they swapped it, and the gauge came alive! Problem was it was a bad sensor and the gauge never moved from 140* regardless of anything.

As you can see QC for these items is pretty terrible, so I'd start with cheap and simple first.

To me your symptoms scream of a bad stat or sensor, not gauge. 

Chrisvr6

I did put in another thermostat. Sensor reads, only when i kill motor then click key back like I'm about to start and it creeps up to 180°.