Engine cooling/thermostat question...
 

The water temp on one of my twin big blocks (with about 60 hours on them since complete pro build) started to rise to close ~180F (they normally both run a max of 150). Oil temp did not rise substantially. I shut the engine down and motored in on one. I pulled the boat out of the water and put it on the hose (as I flush them after use using a Diamond Marine In-line flushing kit) and the temp rose as normal to about 150F (and did not continue to rise)...no issues.
Water flow from the exhaust was normal and equal to the other engine (1988 Formula 311 SR-1).
This seems to indicate that the raw water pumps (Hardin) are working normally.
I am thinking that the thermostat got stuck/jammed for some reason and ultimately cleared when I was on the hose...any other thoughts or ways to trouble shoot without just opening up the (what seems to be a pretty tight/reliable) system?
47440 thermostat housing
https://cimg5.ibsrv.net/gimg/www.off...df9f34fcab.jpg

Running at idle on hose is not a good test to replicate actual running under load on the water. I'm guessing you don't have water pressure gauges??
I highly doubt the T stat would have got stuck closed from debris....stuck open possibly, but stuck closed is not likely
First thing I would do is pull off the water hose that feeds the oil cooler and check for debris or impeller pieces.

Roger! Is there a good diagram showing the flow pattern of this thermostat housing...so I can find the easiest hose to pull to look for debris?
I was hoping that the solid amount of water coming out of the exhaust on the hose would tell me that impeller is good.
Thanks!

I'm thinking its the hardin water pump impeller.
When running in the water the pump should move water thru the motor. If impeller is damaged , then no water. Connect it to the hose and if the impeller is damaged the hose water pressure will push it past the impeller

Roger. I am tending to agree...impeller. Since I have a flushing system with a T, the hose water normally exits the lower drive unit until I start the engine and then it is sucked through the impeller into the engine/exhaust and exits that way. I kinda was leaning away from the impeller being the culprit because this scenario seems to be consistent (hose water out through lower unit until engine starts and then out the exhaust). Maybe the impeller is damaged so that it does not work well enough to cool the engine BUT still appears to be working on the hose.
I believe the ss Hardin's make impeller changing/servicing easier.
Any impeller changing advice?
Thanks!!!

Always ck oil cooler for debris first. Frt of it first. Then I’d Check for Bravoitis too.
https://www.offshoreonly.com/forums/...bravoitis.html

Agree check oil cooler
To check impeller the easy way, Disconnect the hose going from the pump to the thermostat housing at the housing. Connect the hose on the drive and turn water ON. Without the motor running see if water starts coming out the disconnected hose.

If the impeller does need changing its easiest for me (hardin pump is heavy) is remove the pump and change it on the bench. I have the hardin pump and stopped using it after 2 seasons and went back to the Merc composite

Merc composite for weight mainly...or some other issue?

Its weight that had me place on the shelf. To change the impeller I have to hang upside down, there is no room. The added weight just makes it to hard for this old guy.

I agree with Griff. Check the oil cooler inlet first. Take both hoses off and check with a flashlight from the bottom up to see if there is debris blocking the capillary tubes. If there is debris, clear it and see what the debris is. If it's rubber impeller vane pieces, you will know. I found a complete vane in mine after a shop "allegedly" flushed all the hoses.

Most times on the hose, the temp will be close to normal, at least mine does. Curious, but what temp t-stat are you running? I run 160* in mine and the motor runs between 170-175. 180* isn't hot by any means. Personally, I like a little heat in the motor.

That's why I got rid of the whole thing.

Unfortunately, I am not looking at my boat right now as I am on my way back to North Carolina. I have a picture of my port engine (the one that has the higher temps) and (I believe) this is the oil cooler, right?
I am running 140F thermostats and I consistently see no more more than 150-155F water temp although my oil temps spike 180-190F when I am doing a speed run.
Ps-I did NOT note any increase in oil temperature when I was idling around and my water temp started to rise???
https://cimg8.ibsrv.net/gimg/www.off...2d31c82d86.jpg
https://cimg9.ibsrv.net/gimg/www.off...8240777937.jpg

That’s your oil cooler.

that seems like a really small oil cooler to me. maybe not your problem but if you are making 500 plus hp this is the size i run.
https://cimg1.ibsrv.net/gimg/www.off...2c1fff3e4b.jpg

We have similar to Tom’s on the Bullet and never an issue.

Mine are similar to SABER28’s with exception of thermostat rails.

Thanks all...engines are built by a pro and I do see about 190F after a solid speed run but water temps are always in range (except as noted this time).
I can see that this is going to require some contortion to get back there. I wonder if I can snake a remote camera down the water hose for an inspection?

Before getting too deep into it. Take her out again to see if the condition is still there. Something may have been blocking the intake.

Over the winter… add some water pressure gauges to the system. They’re important to have and will alert you to problems before they become a big thing.

I was thinking about doing both (re-run and gauges)...winter is short down in Pensacola :-)

That is your oil cooler that you circled. All you need to is pull off the water hose and feel inside the end of the oil cooler with your fingers for any debris. It is only about a 2-3" deep before you will touch the front plate with the cooling tubes.

Will do!
Can somebody recommend an analog water pressure (or flow) gauge to put inline in my set-up?

Now THAT looks very good!

I have 2 Gaffrig water pressure gauges in like new condition that I would sell for $60 shipped

best thing i see here is............heat exchanger that you can REACH!!!!!!
i wish i had mounted up like this!!!
cant even see mine ...

good luck