Overheat when throttle down

tony1b2000

tony1b2000

Active Member
Oct 10, 2007
243
Salem MA
Boat Info
Carver C37
Engines
Mercury Diesel 4.2 TDI, inboards
Trying to trace the culprit!

Have a 2010 with closed cooling system, 496 mags. When I run at normal RPM's I have no issues. The moment I throttle down to say a no wake zone or basically come to a complete stop, I get over-temp messages on both engines. Guardian mode.
Port shows about 175 on the guage. Starboard, 169 degrees.
Normal temps after about 5 mins so I dont have any issues to dock

Attached picture of vessel view under normal running

I have done the following this year:
1. Changes the Port impeller. ( the old one looked fine, thus will replace starboard next year)
2. Remove / replaced gaskets & turbulators on all riser and extensions. The riser looked a little clogged. cleaned, removed all rust (well, what I could get too), flushed with dock hose water.
3. I did not remove or replace the manifolds as they looked like they had a bit more life in them when I looked when I removed the risers.

Suggestions?
 

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Your water PSI are very high should be 10 to 15 PSI I would look for a restriction in the sea side of the system.
I had a similar issue and found out the water flows from sea pump to power steering cooler then to oil cooler, I found restriction at the oil cooler as it has small tubes in it.
I found seaweed there clean it out and my PSI went to 12 PSI.
Also notice the Water PSI and temperature from the port to starboard motor
The more restriction the higher the PSI and the higher the temperature.
 
Last edited:
Spark600 said:
Your water PSI are very high should be 10 to 15 PSI I would look for a restriction in the sea side of the system.
I had a similar issue and found out the water flows from sea pump to power steering cooler then to oil cooler, I found restriction at the oil cooler as it has small tubes in it.
I found seaweed there clean it out and my PSI went to 12 PSI.
Also notice the Water PSI and temperature from the port to starboard motor
The more restriction the higher the PSI and the higher the temperature.
Click to expand...
Spark, the water routing sounds correct. Is the oil cooler easy to open / clean out? mine is located in the back of the engine. So not that easy to get to...
 
Pull the raw water hoses off both sides of the oil cooler.
If you have a heat exchanger, I'd start there first by pulling the end caps to see if the tubes are clean. Put a flashlight on one end and if you get light thru then your good. Clean the clogged ones. I have found long wooden shickabob sticks do great cleaning the tubes without harming them like a wire coat hanger could.
 
On mine I I remov the hose from the power steering cooler to the oil cooler and then remove the lower hose from the heater exchanger that went to the oil cooler and put a hose in there and pushed it all out

I looked in my heater exchanger several times to find nothing the heater exchanger is the last place the water goes to
 
Spark600 said:
On mine I I remov the hose from the power steering cooler to the oil cooler and then remove the lower hose from the heater exchanger that went to the oil cooler and put a hose in there and pushed it all out

I looked in my heater exchanger several times to find nothing the heater exchanger is the last place the water goes to
Click to expand...


Theres no power steering on a V drive boat
Only manual or hydraulic.
I think you're talking about the transmission cooler and fuel cooler on your boat.
 
You may also have a restriction in the water supply hose from your Bravo drive to the engine. There are plenty of posts about this on CSR with fixes ranging from replacing the hose with a new one to installing a water feed with a thru-hull fitting. There is also a fix available from aftermarket marine. Here's the link for interesting reading near the bottom of this page "bravoitis cure"...

http://www.marine-496pump.com
 
Ok, backflushed the oil cooler. Seeing some improvements already at least on vesselview. Posting before and after pics. Definitely some grass and junk was pushed out!

Thanks for the advice guys!

Do these reading look normal at idle?

Already cleaned risers. Wondering if new manifolds will also help make a difference?? Project for next year....

Results after backflush at idle
After.jpg


Before backflush at idle
Before.jpg
 
Took the boat out yesterday after flushing oil cooler. Still overheat error message when throttling down.
Suggestions?
 
Your water pressure is high indicating a restriction down stream. How's the inside of your heat exchanger look?
 
scoflaw said:
Your water pressure is high indicating a restriction down stream. How's the inside of your heat exchanger look?
Click to expand...

I agree with this....

Are you still seeing 30+psi water pressure at 3400 rpm as shown in your first photo?

If so, I would suspect a blockage after the water pressure sensor.

Keep at it and you'll find the issue.
 
Exhaust blockage seems like a possibility sometimes the butterfly valves become lodged in the y pipe near the exhaust outlet when at higher rpm no problems because the pressure of exhaust gasses keeps the offending piece out of the way then idle down it obstructs just a thought after all you've done
 
Do you think it's just an issue when I throttle down quick and the butterfly valves are closing? Problem goes away after 30 seconds and back to normal temps.

Here is a picture running at 3000 rpms after I flushed the oil cooler....
At the dock of course in neutral.
After.jpg
 
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