View Full Version : 240 efi head temp on hose

12-02-09, 05:02 PM
I have an '02 utopia with the merc 240 efi motor. Last weekend I had it hooked up to the flushing hose and ran it at idle for about 5 minutes.

I noticed something that seemed strange - the port head was cool to the touch, and the starboard head was quite warm to the touch ( not overheating hot, but fully warmed up.) Also, no water comes out the tell-tale while on the hose, although it does in the water.

Is this normal? If no water comes out the tell-tale, then is the motor getting fully flushed? I understand there are no thermostats in this motor - is that true?

12-03-09, 12:31 AM
The problem with running the Mercury on the hose, is that with the design of the cooling system most of the water runs right down through the ride plate and out the pump. For that reason it's common not to get water out of the tell-tale and is why you should never run the engine above idle and don't run it for more than about ten minuets. To answer your last question, you're correct, there is no thermostat in the Mercury.


12-03-09, 07:13 PM
thanks - any opinion on one head warm and one head cool on hose? Is this something to be concerned about -ie obstructed internal passages - or just a quirk of the flushing attachment?

02-13-10, 01:21 AM
i have a merc 210 carbed and noticed the same head temp difference when i ran it on the driveway after removing the oil injection- it looks like the water goes into port and is then routed right there with a "T" to starboard - maybe less water going to it. seems like a "T" in the hose farther down and then 2 lines - one each to each head would equalize the flows and temps better - but I just have an engineering degree - I don't use it :)