Water pump on F250 4.2

[wrxhoon]

My water pump was due for service. I got a genuine Yamaha kit rather than just replace the impeller .
When I pull it apart the old impeller was a bit damaged but she never overheated . I wouldn't know the pressure as Yamaha don't give you pressure gauge, pretty silly really , Mercury does. In my opinion water pressure gauge is better than temp gauge.
After replacing all parts I put it together and drop the motor in a tub to test it, to my surprise I didn't notice a lot of difference in the telltale . I would have thought she would be peeing a lot more water with the new pump. The only part reused was the plastic cover and the seal on the tube that goes to the motor as they weren't included in the kit.
My question to you guys with any 4.2 engine, how hard does the water come out of the telltale? Photo or video if possible.
Thanks in advance ..

 

[Halfhitch]

I had a 2018, 4.2L F225 I bought new. I noticed from the very start that the pee stream was very weak. That being said though, it never did sound a heat alarm.

Very soon Ky Grady is taking delivery on a new 4.2L F250 so he will have some insight soon.

 

[Ky Grady]

Impatiently waiting on that motor by the way. At least mine is not a have to repower, it's a want to repower. F225 still purring along.

Yamaha's are not known for a strong pee stream anyway. As long as you never tripped an overheat alarm, you should be good.

 

[Legend]

I have a pair of the F250s 4.2L and the stream is a bit light. When flushing the engines I often seen one side or the other peeing. While running it is still not what you would consider a strong stream, guess its just the design. Mine are 3 years old and have had one water pump change out, No difference in the stream since new.

 

[wspitler]

If you have the standard Yamaha gauges or the newer ones, you should have engine temperatures. That is what is most important. You could have high water pressure with a stuck thermostat or some other blockage and overheat the engine so what really matters is the temperature. I have one engine that has a very weak stream and the other one very strong they both run at stock temperatures. About 145-155 F if I remember correctly. My advice, don’t worry about it and watch the temperature gauges.

 

[seasick]

If you have the standard Yamaha gauges or the newer ones, you should have engine temperatures. That is what is most important. You could have high water pressure with a stuck thermostat or some other blockage and overheat the engine so what really matters is the temperature. I have one engine that has a very weak stream and the other one very strong they both run at stock temperatures. About 145-155 F if I remember correctly. My advice, don’t worry about it and watch the temperature gauges.

It is possible that in the case of total water flow loss, the engine will not be cooled but the temperature sensor doesn't know that right away . By the time it does, it may be too late.
Water pressure is a better measurement but that also depends on the actual plumbing and where the pressure is measured.

 

[wspitler]

Good points! The fail-safe is that there are two overheat switches, one in each head that will sound off if the engine overheats, It's not quite that simple, since the ECU looks at other things such as running time and RPM before initiating the alarm. Those sensors don't care about water flow and will protect the engine from damage as they are set below the engine damage temps. I seem to remember that some have a reduced power mode associated with the alarm in an attempt to prevent someone continuing to operate if they don't hear or disregard the warning.

 

[Ky Grady]

Correct, the motor will go into a limp mode per se, to protect itself.

 

[wrxhoon]

Thanks for taking the time to reply. As you can see the temp gauge is next to useless , it just shows that it is within range indeed right in the middle . I would be much happier if it showed actual temp.
As I found some marks on the old impeller I thought I would get a lot more volume out of the telltale with the new pump kit installed .
I even used a tub to run it rather than earmuffs. I normally use earmuffs and tape the 2 pickups, even then I never had any alarms and I run it for at least 10 minutes at 600 RPM.
As I said before I never had any alarms before, the reason for the pump service was the fact that it was due for impeller change and I decided to install a full genuine kit . I understand that if she overheats alarm will go off but that is no help when I'm 30-40 miles offshore.
Maybe time for a new Merc V8.

 

[wspitler]

You can install an optional water pressure sender if it makes you feel better. You can also monitor actual temps with YDIS ($60) (https://www.ebay.com/itm/Diagnostic...ine-Outboard-WaveRunner-Jet-Boat/272277218057) or via the NMEA2K network on most MFDs. The ECU sends the actual temp, but the gauge is a bar gauge like your fuel gauge. I too was worried about a weak pee stream on my starboard engine and that was two water pumps and 700 hours ago. I can see that when my gauge is in the center the temps are about 140 F. Probably the same as yours. Both Mercs and Yamahas are seriously reliable these days.

 

[seasick]

Are you folks sure that a high temp alarm triggers a limp mode? I am not sure about that model motor.

Usually in Yamaha parlance the thermo switch is a device that 'trips' at a set temperature, an on off type of device. On the other hand, a thermo sensor measures actual temps across a range, a variable output signal.
It looks like the 225 has 2 thermo switches, one in each t-stat housing but I don't see a thermo sensor in the diagram. As I mentioned, I don't have hands on experience with the F225.

My point about overheating when there is no water is that the water conducts heat from the cylinder to the cooling chambers and eventually throughout the cooling system. Water is a good conductor but air is a very poor conductor. Yes, in the case of very low or no water, the sensors will eventually get quite hot but the internal cylinder parts will get hot a lot quicker, hence the delay in the sensor triggering.

 

[Doc Stressor]

Water in the cooling system actually slows the rate of tripping the thermo-switch in the cylinder head. Aluminum conducts heat very well.

In my experience, the thermo-switches work very well for preventing damage in the event of water flow interruption. When I lived in the Pacific NW, my engine would overheat several times during most trips when kelp would wrap around the lower unit and completely block the water intake. That engine is still running fine 23 year later.

 

[seasick]

I was thinking about my older experiences with cast iron blocks and heads. Your point is well taken.

 

[Punch53]

On my friends boat the pee stream was non existant but the motor wasn't overheating. It seems some models pee stream water passes through a heat sink that cools the electronics. Cleaned it out with salt-away and it works fine now.

 

[seasick]

On my friends boat the pee stream was non existant but the motor wasn't overheating. It seems some models pee stream water passes through a heat sink that cools the electronics. Cleaned it out with salt-away and it works fine now.

On Optimaxs, water comes from the pump , through the air compressor and out the telltale port. It doesn't tell you at all if the rest of the motor is getting cooling water. If it stops peeing, you will cook your compressor, a very expensive event.
The second pump output cools the block of course but also the fuel rail and in some versions, the ECU.
In summary, on my Yami, no pee stream, maybe not a terrible thing. On the Mercs it's a different story

 

[Doc Stressor]

You should always see some water coming out of the tell tail. If there is no water flowing at higher rpm, you can overheat the rectifier. When the batteries are fully charged the excess current from the alternator is dissipated as heat at the rectifier heat sink. That's why it is water cooled.

I had my cooling system on my old F250 gunked up with silt after slogging through a shallow canal at low tide. I ignored the lack of water coming out of my tell tails since the engine did not overheat. But when the batteries were not charging after a long trip I realized that I had a problem. It turned out that the thin cooling pathway to the rectifier was completely blocked by mud. I needed to flush the tubing and hoses out, which was not easy, and replace the rectifier.