Higher Engine Temps After Cooling Service

[Thelog]

After running the Penray online cleaner for 30 days, I flushed the engines (8V71TI) and replaced the coolant with distilled water and Detroit Diesel Powercool Plus 6000. At the dock, the engines warmed up like normal. Once under load at speed, both engines heated up to 185 simultaneously. They have never been that hot before. I assume I missed something along the way. Is there air that needs to be bled from the system somewhere? Did I skip a step? Please help! Spending the night on the hook and will tackle this in the morning (if I can sleep)... I appreciate any responses!

 

[SEVEN]

You could have an air block. Open the cap and drain each pitcock. Re check your fill of coolant and fill. Hope that helps.

 

[captddis]

Too much coolant will cause over heating. No more then 50% should be used.

 

[Thelog]

Thanks for the replies! I tried burping the system as best I could. Ran back to the dock late last night and temps were still elevated. I'm using an OAT inhibitor/water only solution with no coolant. I assume my next step is to pull the thermostats, which I should have done anyway during the service. Other than eventual carbon buildup, is it a bad idea to run the engines with no thermostats during a Miami summer? Last night the bay water was in the mid 80°s. In July/August they push 90°.

 

[Avenger]

What temp did they run at before you serviced them? Will they maintain 185° under load, or do they still climb?

Do not leave the t-stats out.

 

[SEVEN]

You might want to check your impellers as well. Probably not the issue since both engines increased heat. However it's not going to hurt.

 

[steve c]

I chased an overheat problem last summer from the wrong end! Changed coolant, cleaned thermostat,intercoolers,heat exchangers.Changed thermostats, impellers and even some hoses.
Strainers were immaculate. I started on the wrong end. The holes in the scoops on the hull were almost filled with deposits. I had a diver clean them the best he could. Problem solved. Over the winter layup I enlarged all of the 1/32 holes to appx. 3/16". Like I said, I started on the wrong end.

 

[Thelog]

Prior to this service they would cruise just over 175° except for July-September they would creep just to the right of the 180° hash mark. Last night, they stabilized at 185° and stayed there.

Although the exhaust water flow seemed normal, I will definitely check the impellers and intake/strainer as well.

Thanks!!

 

[Finalee]

It sounds like the thermostats may have been stuck open prior to the service. I would replace them just out of general principle.

 

[SKYCHENEY]

Replace thermostats and seals. I had one sticking and not fully opening once.

Its hard to believe it would happen on both engines at the same time, however.

 

[Boatsb]

Or the sender's are now clean and reports accurate temps.

 

[SEVEN]

Great point Bob.

 

[Summerfun]

If you are switching from green coolant to water with corosion inhibitor then that may be a bit of an issue that would be like going from green coolant to red. It was explained to me that the green coolant stops corrosion by adding a thin film on all wetted surfaces. That works with that coolant to protect corosuion and transfer heat. Red coolant like the water and addative have the addative to protect corrosion. If you switched with no flushing or cleaning to remove that film that may be affecting heat transfer. Not sure if this is your issue but something to think about.

 

[Thelog]

Thanks to everyone for helping me out with this! As it turns out, it looks like I had the wrong ratio mixed in. I went by the mixing rate printed on the back of the bottle, that called for 12.5% by volume. During my obsessive research for a solution, I found a Detroit Diesel Service Bulletin online that called for 7.5% by volume. After switching to the latter solution rate, I took the boat for a spin, and the engines were back to normal. Prior to taking my next extended run, I will definitely check my impellers and change out the thermostats as suggested. I will also be doing a Genesis inspired acid wash through the raw water side.

This website and its members are an invaluable resource. When I come on here, I feel like I'm standing among giants. I have a lot to learn and a long way to go!

 

[SEVEN]

Glad it all worked out. Luckily it was an easy fix. This site is great!!!!!!

 

[Finalee]

Thanks for posting the final outcome.