OMC 4.3 Water Temp Gauge went to zero after reaching 220..

[millermankjm]

New boat, 1988 Four Winns Horizon 180 with OMC 4.3 and Cobra outdrive. Got it started after being down for about 2 years sitting. Appears my choke is not closing all the way so have to encourage with a bit of starter fluid sprayed into carb venturi with choke flap open. Starts and idles at 800 rpm. So far so good. Ran for 10 minutes and monitored all the gauges and saw the water temp gauge rise gradually to 220 or so and then started falling until it went to zero. Thinking that the sensor is not getting any water on it to tell water temp gauge true water temp or gauge is bad. Took boat back in and held off running till tonight and ran for 20 minutes without any issues except gauge still to the left at zero. Felt hoses and they were warm but not untouchable. I have another boat, same vintage Four Winns 200 with another 4.3 I recall which I got for free with a nice trailer as the guy wanted it out of his storage yard by an long gone renter. So my basic question is, without proper working water temp gauge and or temp sender, how can you tell if an engine is overheating? I know a car engine will lose power and overheat through the radiator cooling system but this boat has an open system pumping raw water through the engine block. Just don't want to damage the engine by running if it could be getting too hot and not showing signs of such. Will be swapping out gauge first then sensor that was on the other boat to see if that works. Saw that to test impeller is to remove the raw source water pipe and look for a stream 2 to 4 inches high when held up so I do that test too.
Other question is hearing a erratic clunking at low forward speed every say 3-4 seconds but not with a higher forward speed. Almost like it is popping in and out of gear at low forward speed but not that actually happening.
Final question is my power tilt "shocks" have no stay.. and void of fluid. Assume there is a resivoir to try check level and fill if necessary. Have not got the boat up to plane yet as on a pond with only headway speed limit. Will move to big water to test planing but with no fluid holding the outdrive still, reverse will be very slow. so as the outdrive does not ride up due to no pressure in those "shocks".
Thanks in advance for any help! I'm like a new boater on the day he gets his boat and the day he sells it!

 

[Scott Danforth]

Anything over 170 is an overheat

Going to 220 man's that you have no water flow from the impeller

Do an impeller job, pull the drive and do an alignment check, etc

Do not run the boat until you fix the raw water pump

Do a compression test. An overheat usually collapses the pistons

You will have to also pull the exhaust elbows because you toasted the exhaust flappers and hoses due to lack of cooling water

 

[millermankjm]

Thanks for the great info.. The temp I mentioned might be wrong but 160 seems really low.. What is the typical thermostat rating in these 4.3s? I will pull the gauge and sensor to check specs ..

 

[Scott Danforth]

Thanks for the great info.. The temp I mentioned might be wrong but 160 seems really low.. What is the typical thermostat rating in these 4.3s? I will pull the gauge and sensor to check specs ..

Stop thinking automotive.

140 degrees for a raw water cooled carbureted motor

160 degrees for a heat exchanger cooled motor with a carburetor, or EFI and raw water cooled

180 degrees for heat exchanger cooled EFI

Anything over 170 on a carbureted marine motor is an overheat

Raw water impellers do not survive sitting. They also only last a few years regardless of use.

When you pull the impeller, make sure to pull the system apart to find the missing bits of your toasted impeller

 

[Scott Danforth]

Just an FYI, any surface over 200f is considered an ignition source.

 

[Lou C]

OMC's standard thermostat is 160* in the 21 years I've owned this boat I have found that normal operating temperature is 160-175 and the 175 is only after coming off plane, the temp soon drops back to 160
220* you for sure melted the flappers, depending on how long you ran it at that temp and could have damaged the head gaskets and cracked cyl heads.
If very brief, might be OK
the other things that can get damaged by overheats that many miss are the water tube gaskets in the outdrive, if these get melted by the lack of cooling water then your raw water volume may be too low
The Cobra water pump is about the easiest one to do I have ever seen. Use OEM parts, change it every 3 seasons depending on use (deep water vs shallow sandy water).
In an automotive app these engines normally run at 195-200 degrees, but marine open systems are not pressurized and the water will boil inside the cyl heads at a bit over 200 unlike a closed pressurized system where it won't boil till 260 or so.
The business about salt and or calcium deposits over 160* I have not found to be true at least in Long Island salt water. Had the heads off after 15+ years of use, no clogged passages anywhere. So no reason to not use a 160* stat, I tried a 140 and the engine took forever to warm up and I had condensation in the exhaust manifolds. So went back to the 160*

Get an IR temp gun it will help with keeping your engine at the right temps
with the gauge reading 160*, the intake manifold right under the stat housing will read 145-155*, that's the most accurate spot I've found for getting running temps
at idle your exhaust elbows will read about 100-110
after coming off plane, about 135-140 but they will soon cool back down to 120 or so
this is what I've seen on the same engine over these 20 years of use.

 

[millermankjm]

OMC's standard thermostat is 160* in the 21 years I've owned this boat I have found that normal operating temperature is 160-175 and the 175 is only after coming off plane, the temp soon drops back to 160
220* you for sure melted the flappers, depending on how long you ran it at that temp and could have damaged the head gaskets and cracked cyl heads.
If very brief, might be OK
the other things that can get damaged by overheats that many miss are the water tube gaskets in the outdrive, if these get melted by the lack of cooling water then your raw water volume may be too low
The Cobra water pump is about the easiest one to do I have ever seen. Use OEM parts, change it every 3 seasons depending on use (deep water vs shallow sandy water).
In an automotive app these engines normally run at 195-200 degrees, but marine open systems are not pressurized and the water will boil inside the cyl heads at a bit over 200 unlike a closed pressurized system where it won't boil till 260 or so.
The business about salt and or calcium deposits over 160* I have not found to be true at least in Long Island salt water. Had the heads off after 15+ years of use, no clogged passages anywhere. So no reason to not use a 160* stat, I tried a 140 and the engine took forever to warm up and I had condensation in the exhaust manifolds. So went back to the 160*

Get an IR temp gun it will help with keeping your engine at the right temps
with the gauge reading 160*, the intake manifold right under the stat housing will read 145-155*, that's the most accurate spot I've found for getting running temps
at idle your exhaust elbows will read about 100-110
after coming off plane, about 135-140 but they will soon cool back down to 120 or so
this is what I've seen on the same engine over these 20 years of use.

This is great info for a marine newbie. So before I posted this, I did run it a second time thinking that the engine would have shown signs of bogging etc which it did not. Again, I will not run again until I check out the things above. I have spend a few hours getting it ready and being very cautious about overtemp. The temp gauge was not at +200 for very long but as you said, if a raw water system is normally down at 160, then yes, it wasnt so good to run after that. I bad!

Question, how to test my water temp sensor.. Can I put the element into water and check the resistance assuming that it would go to zero or close so that the gauge would draw more current through it when sensor gets hot?

 

[Scott Danforth]

Do a resistance check

However, the gauge is the last thing to get to after the other items

 

[millermankjm]

Do a resistance check

However, the gauge is the last thing to get to after the other items

Great video on testing sender and gauge for a Mercruiser. Is this the same setup for an OMC?

 

[Lou C]

It’s similar except OMC said to heat oil instead of water for the water temp test I guess because it won’t boil so you can get higher readings. Don’t do this on a gas stove!

When you get no reading on a water temp gauge & the sending unit & gauge are good that could mean there is no water in the area where the temp sensor is! That happened years ago to a friend with a Dodge Dart with a slant six. Pinhole leak in the water pump rad was almost empty! I filled it up with AF for her & she drove it back to NJ & had a new water pump put in! And the engine still ran!
They don’t build em like they used to….

 

[millermankjm]

It’s similar except OMC said to heat oil instead of water for the water temp test I guess because it won’t boil so you can get higher readings. Don’t do this on a gas stove!

When you get no reading on a water temp gauge & the sending unit & gauge are good that could mean there is no water in the area where the temp sensor is! That happened years ago to a friend with a Dodge Dart with a slant six. Pinhole leak in the water pump rad was almost empty! I filled it up with AF for her & she drove it back to NJ & had a new water pump put in! And the engine still ran!
They don’t build em like they used to….

Okay, sorry for the delay in getting back on this..
Next time out we checked the flow from the outdrive and it was working but not very strong.. There was water flowing out to the input to the engine of the supply hose so the engine is storing some water. Flow at idle was like 1/2" to 1" so definitely not dry.
We launched and monitored the temp gauge. Note that we were in a river which was pretty cool according to my shipmate. I checked the water pump hose and it got warm but not hot so its not overheating.. Temp gauge stayed at 100 or less.. left edge of gauge.
At the entrance to the lake about 1/2 mile down from where we launched up river still no movement on the gauge still checking the hoses for temp.. Nothing hot but warm.
Now the fun. Sandbar in main channel as the river meets the lake.. I took a side tributary which was not what I should have done! Weeds started to clog the prop and so did the same type of sandbar so wondering the depth in that murkey brown water found it to be about a knee depth! Wow, thought I'd see the bottom but lots of particles in the water from the river made it dark in color and less flow from the direct entrance to the lake... So now more fun.. we not only had weeds but also sand.. and guess where the temp gauge moved! We shutdown to figure our situation and what to do.. Decided to pull up the outdrive.. by hand as my tilt system was not functional.. Drop my body into the murk, cleaned the prop of weeds and pushed the boat away from the low sandbar back to the main channel and faced the original sandbar. Note where the outdrive was stuck created quite a deep hole which I took a dip in.. ooooh it was cold!
Got the boat out of there and restarted after getting back in. Temp down as expected to 100.. Now we putted over the main sandbar and then out to the lake. through the 4 channel markers.. RRR I remember so we stayed to the right of the red ones.
As it was getting late, we decided we had enough fun and headed back up river with the outdrive held up by rope. Just didn't go any faster that headway back so it was a longer trip to the launch but did get the handheld hand lamp with 2k lumens going just to be sure we didn't miss any obstacles on return.
Relieved that the trip was done and no big issues to deal with we popped it on the trailer and pulled out.. Note that one last newbie mistake...was that I didn't winch up the boat as far as I should before taking off from the parking lot..so the drive home felt a bit odd.. Kinda like lots of water in the bilge.. tail heavy.. Needless to say when I detached to trailer from the truck.. not enough tongue weight so up she came by itself so rest on the outdrive somewhat gently on the sandy yard!
Lessons learned...
1) Always have someone more knowledgeable when you are not sure about your upcoming trip. Thanks Randall for that knowledge on our trip!
2) Make sure you know the depth of the waterway. We did ask as we past others heading back. They said stay to the right of the river on exiting. Think we did but that outdrive down was the fail here.. Make sure you tilt is working!!
3) Don't assume that dark water is deep!
4) Winch up your boat to the shortest length of cable and not just touching the Y mount on the trailer.. Could have been a safety chain event!
5) Ensure you are prepared .. we did! Had a trolling motor with a fully charged big battery on top of the boat battery just in case your "new boat" engine acts up .. This was helpful when I wanted a break from pushing by hand.. I'm an old duffer and it got me out of the cold murk much sooner... Not hypertherm territory but was glad to get back on board! Thanks to Randall's boat shoes I borrowed when in the muck!

So gonna get a new outdrive impeller, new cage it spins in (according to Randall), a new thermostat and test the sensor at various voltages to see what the temp gauge does..

Hoping to get some more time in the water for foliage season coming up but want my wife to know I did my due diligence prior to launching!

 

[Outlw36]

Okay, sorry for the delay in getting back on this..
Next time out we checked the flow from the outdrive and it was working but not very strong.. There was water flowing out to the input to the engine of the supply hose so the engine is storing some water. Flow at idle was like 1/2" to 1" so definitely not dry.
We launched and monitored the temp gauge. Note that we were in a river which was pretty cool according to my shipmate. I checked the water pump hose and it got warm but not hot so its not overheating.. Temp gauge stayed at 100 or less.. left edge of gauge.
At the entrance to the lake about 1/2 mile down from where we launched up river still no movement on the gauge still checking the hoses for temp.. Nothing hot but warm.
Now the fun. Sandbar in main channel as the river meets the lake.. I took a side tributary which was not what I should have done! Weeds started to clog the prop and so did the same type of sandbar so wondering the depth in that murkey brown water found it to be about a knee depth! Wow, thought I'd see the bottom but lots of particles in the water from the river made it dark in color and less flow from the direct entrance to the lake... So now more fun.. we not only had weeds but also sand.. and guess where the temp gauge moved! We shutdown to figure our situation and what to do.. Decided to pull up the outdrive.. by hand as my tilt system was not functional.. Drop my body into the murk, cleaned the prop of weeds and pushed the boat away from the low sandbar back to the main channel and faced the original sandbar. Note where the outdrive was stuck created quite a deep hole which I took a dip in.. ooooh it was cold!
Got the boat out of there and restarted after getting back in. Temp down as expected to 100.. Now we putted over the main sandbar and then out to the lake. through the 4 channel markers.. RRR I remember so we stayed to the right of the red ones.
As it was getting late, we decided we had enough fun and headed back up river with the outdrive held up by rope. Just didn't go any faster that headway back so it was a longer trip to the launch but did get the handheld hand lamp with 2k lumens going just to be sure we didn't miss any obstacles on return.
Relieved that the trip was done and no big issues to deal with we popped it on the trailer and pulled out.. Note that one last newbie mistake...was that I didn't winch up the boat as far as I should before taking off from the parking lot..so the drive home felt a bit odd.. Kinda like lots of water in the bilge.. tail heavy.. Needless to say when I detached to trailer from the truck.. not enough tongue weight so up she came by itself so rest on the outdrive somewhat gently on the sandy yard!
Lessons learned...
1) Always have someone more knowledgeable when you are not sure about your upcoming trip. Thanks Randall for that knowledge on our trip!
2) Make sure you know the depth of the waterway. We did ask as we past others heading back. They said stay to the right of the river on exiting. Think we did but that outdrive down was the fail here.. Make sure you tilt is working!!
3) Don't assume that dark water is deep!
4) Winch up your boat to the shortest length of cable and not just touching the Y mount on the trailer.. Could have been a safety chain event!
5) Ensure you are prepared .. we did! Had a trolling motor with a fully charged big battery on top of the boat battery just in case your "new boat" engine acts up .. This was helpful when I wanted a break from pushing by hand.. I'm an old duffer and it got me out of the cold murk much sooner... Not hypertherm territory but was glad to get back on board! Thanks to Randall's boat shoes I borrowed when in the muck!

So gonna get a new outdrive impeller, new cage it spins in (according to Randall), a new thermostat and test the sensor at various voltages to see what the temp gauge does..

Hoping to get some more time in the water for foliage season coming up but want my wife to know I did my due diligence prior to launching!

sounds like you also need to invest in a depth finder