Curious about Mercury hose routing on V engines. Come on big guns, let's hear from y

Mercury V6 engine cooling hose routing has been on the Merc forum a few times recently and I have a puzzling question that has intrigued me for many years and seems like time to ask about it.

My son had a '96 as I recall Merc 150, V6 2 liter. It had thermostats at the top of each bank of cylinders and a high rpm popoff coming off the top of the block via a hose and dumping into the mid section.

The tell tale was plumbed off the output of both stats in parallel off to a single hose that was the tell tale teed off the dump hose for the stats. The stats and the popoff did not join each other with flow from their outputs like I think my 90 does....can't find proof one way or the other on it.

As a result of this plumbing you don't know if you have cooling to your engine until the water in the block gets up to around 150F. Then one/both stat(s) open and you get some miserable spurting out your tell tale until the stat cools off and shuts if off, which at idle, especially in cold water isn't very long....measured in seconds.

So what's the point of the tell tale? To me the most important time to know that your water pump is working is when you are launching your boat and first crank up your engine. I want to know before I back off the trailer that I have cooling water. Real stupid design as far as I'm concerned.

So, on my son's engine, I moved the tell tale from the stat output to the hose coming from the top of the block sampling cooling water in the block's water jacket that goes to the pop off valve. In this configuration, I have a nice solid stream of water out the tell tale as soon as the block fills which is a matter of 10's of seconds. Knowing that I/he can launch and go and enjoy a days boating.

So in short, what is your opinion, or do you know as to why Merc decided to do the tell plumbing as they do?

Surely others with those engines are interested in the answer.

Thanks,
Mark

Re: Curious about Mercury hose routing on V engines. Come on big guns, let's hear fr

I had a 175 merc. While the tell tale was weak at best, it did start flowing as soon as the block as full.

The thermostats are “vented”. There should be flow past/thru thermostats at all times. I would check to make sure the thermostat "vents" are not clogged and the poppet is in good working order (spring not damaged). I had a similar issue until I rebuilt the poppet assembly

Re: Curious about Mercury hose routing on V engines. Come on big guns, let's hear fr

Thanks ding. I thought this thread would die on the vine.

I am aware of the vent hole. I looked at the diameter of the holes and they looked small to vent very much, even into the 5/16-3/8 drain tube, and the fact that the pee is teed off the dump line at right angles to the line from the stats, meaning that the dump line has to fill with water before the pee has pressure to drive water out of it.

Ok I think I am reading that your poppet had a bad spring, thus couldn't maintain the valve closed till the engine got to spec rpms. That would keep the block draining big time and not allow the stats to heat the water in the block to opening temp. Makes sense.

Thanks,
Mark

Re: Curious about Mercury hose routing on V engines. Come on big guns, let's hear fr

Texasmark said:

Ok I think I am reading that your poppet had a bad spring, thus couldn't maintain the valve closed till the engine got to spec rpms. That would keep the block draining big time and not allow the stats to heat the water in the block to opening temp. Makes sense.

Thanks,
Mark

Click to expand...

The stats worked fine. The poppet is the systems pressure regulator. The poppet malfunction dropped the system pressure just enough to affect the tell tale flow with the stats closed at idle.

Spring looked fine. Old spring maybe 1/8" shorter than replacement. Made a big difference