2004 DF70 overheating over 3000rpm

[Dos Caņas]

My 2004 D70 was giving an over-temperature alarm within about 20 secs of going over 3000rpm. Back on the dock, the tell-tale looked fine both at idle and on flush.
With the thermostat removed, it seems to run ok. However, with a replacement thermostat, the alarm returns. My mechanic has suggested replacing the impeller, but I am not convinced this is the problem. I think it might be the water pressure valve (pop-it/poppet valve spelling?).
I have searched for and read lots of stuff about this valve online, but a lot of it is contradictory. Some say a faulty water pressure valve would give over-temp problems at low rpm, but others say the opposite, and the alarms would be at higher rpm.
I found a few threads on here about similar issues, but none of them resulted in a final solution.
CAn anyone help?

[Murray]

https://www.boats.net/catalog/suzuki...001/thermostat

Part #7 $16. If your suspicious of your water pressure valve for $16 it might be worth changing it out. When was the water pump last serviced? Keep in mind that your telltale only shows the impeller is spinning not the efficiency of it’s pumping ability.

[Dos Caņas]

I don't know when the impeller was last changed. I've had the boat just over 2 years and put 50 hours on the engine, so at least that long. Hopefully, I get the pressure valve out of it at the weekend.

[Murray]

I’d be inclined to change the water pump first, Suzuki recommends 100 hours or yearly. Suzuki sells water pump kits, thats the route I’d go then your starting fresh. You can still change out the water pressures valve. Is this a saltwater engine?

[Dos Caņas]

Yes, itīs kept in salt water, El Puerto de Santa Maria, Cadiz, Spain. Before reading your last post, I pulled the pressure valve out, and it looks ok. So looks like both you and the mechanic were right. Hopefully, a water pump kit will solve the problem.
Itīs just that Iīm on to my 3rd mechanic in as many years after 2 bad experiences. Current one seems a lot better although itīs a Mercury dealership. Suzuki have no real support where I live.
Boat needs to come out anyway as itīs due a ībum cleanĻ.

[Murray]

Could be deposits from running in salt water and not flushing with fresh water after use but I’d change out the entire water pump first and go from there.

[Dos Caņas]

The previous owner kept the boat on a trailer in a shed but it's been in salt water for just over 2 years now. I have access to fresh water at my dock and always give it a good flush.
I've attached 2 pics of thermostat cover and where it goes. Does the build up look normal or excessive to you.

[Murray]

Sorry can’t help you there, I’m a freshwater guy.

[Solarman]

Looks like you should run the foot it in a bucket deep enough to cover the water pump, using vinegar, or another corrosion cleaner (vinegar is usually much cheaper). If let it idle in neutral with the same solution for a couple hours (the solution will get hot after about 20 mins, top off the solution let it cool for couple hours, then run another 20 mins) total time. After the flush take out to test/ and flush the solution. If running in saltwater, flush it normally with freshwater.

If you go for the water pump change out first check to see that solves you problems.

If still having issues, check to see if you have an additional sub-cooling water pipe (s/s pipe running from above the prop to just below the water pump)? If it does, inspect those rubber grommets (both ends) to see if burnt-out/ loose/or worn out. If damaged replace them. Damaged grommets allow exhaust to blow into the cavity below the pump causing interference for water to get pumped at higher rpms, usually above 2000 rpms. Some motors have this sub cooling water pipe?

Good luck, post back on what you do/ find out.

[Dos Caņas]

I was thinking of using vinegar. Our fresh water here is very hard and I use it for cleaning the bathroom etc