Mercury over heating

[84Ranger]

I have an over heating problem on my 1984 Mercury black maxx 150 V6. I have already replace all new carb gasket, fuel pump kit, new water pump kit with impeller, and inspect for any fuel and water restriction and is all ok. took it out again and still after a minute on WOT the over heating alarm came on again. I need help on looking for the poppet valve....I don't know where it is at and where on the carb do I adjust for air and fuel mix.....think Im running lean.....any suggestion would be great....thanks

 

[j_martin]

Re: Mercury over heating

I have an over heating problem on my 1984 Mercury black maxx 150 V6. I have already replace all new carb gasket, fuel pump kit, new water pump kit with impeller, and inspect for any fuel and water restriction and is all ok. took it out again and still after a minute on WOT the over heating alarm came on again. I need help on looking for the poppet valve....I don't know where it is at and where on the carb do I adjust for air and fuel mix.....think Im running lean.....any suggestion would be great....thanks

A water pressure gauge is about the best bet for troubleshooting cooling issues.

The poppit is low on the block, just above the exhaust plate on the starboard side. It has either 2 or 4 bolts holding it on. There's an O shaped grommet or gasket in the block that sometimes sticks to the valve and prevents it from opening. Easy to work on. Just have gaskets handy when you open it up.

The pressure gauge is a dynamic indicator that can tell you all you need to know about the cooling system at a glance.

What carbs do you have. None of the V6 carbs have high speed adjustments on them. If you could give me the numbers off'n any one carb, I could tell you the jet sizes for them. Stock is usually plenty fat unless you have mods on it like stacks that force more air in.

The most likely cause of lean burn at WOT is just plain fuel delivery problems. That could be anything. In my personal experience:
Tank pickup screen
Pinholes in suction line
Bad primer bulb
Wrong (plastic aftermarket) bayonet fittings
fuel pump
fuel pump pulse hose (tygon is too soft)
wrong fuel line (too small, aftermarket)\
plugged fuel filter
carb float adjustment

If you plan to do any work on it, get a mercury service manual for it.

hope it helps
John

 

[hkeiner]

Re: Mercury over heating

The recommendation for installing a water pressure gauge is very good advice. Here is a link explaining more about the benefits and how to install it on a V6.

http://www.diy-boat.com/index.php?option=com_content&task=view&id=151&Itemid=49

 

[84Ranger]

Re: Mercury over heating

Sorry guys forgot to put down that I have a water pressure gauge and when it over heat it reading 22 to 25psi at 4 to 5,000 rpm.....I think that is good.....could be a fuel problem....and how do u adjust the carb float and where are the adjusting screw or bolt for that. and yes I order a manual already and wont get it till next week.....how can I tell if I have a fuel filter..cause I look for a fuel filter and can't seen to find one on any of the fuel line....could there be no fuel filter....how can u tell if the primer bulb is bad? On the tank pick up screen do I have to remove the tank or can I just unbolt It from the tank......I notice that since the over heating started it has had a hard starting problem and will not start right away or with one crank......I have to shift (throttle cable) forward to open the plate in the carb for it to start...just like starting when cold......and will not start with just a crank anymore after warm up...before the motor starts ok at anytime........it really driving me crazy......I have to check all my fuel lines again and in the fuel tank too. thanks again

 

[j_martin]

Re: Mercury over heating

You should number your questions so the answers can be numbered.

Anyway, if you suspect fuel delivery problems, there is a procecedure where you put a vacuum gauge in just before the fuel pump and see what happens. Another part of that procedure involves installing a short piece of clear vinyl line in the fuel line. The object is to find suction restrictions, like a plugged pickup screen, or air intrusion through small leaks anywhere they may be.

your water pressure seems to be a bit high. It indicates that water is getting to the power head, but having trouble getting out.

Does the pressure "step back" a bit at about 2 - 3000 rpm. It should drop slightly when the poppit opens. If the poppit is plugged, you would have high pressure and overheat.

I ran over a rotten log, cutting it in half with my XR4 once. Took me a month to pick out all the toothpicks from the cooling passages and get it to run cool again.

It's possible there's no fuel filter. If the carbs are the "final filter", that's probably where your trouble is.

The only adjustments on the carb are jet changes, and the tang on the floats adjusting float height. They have a muriad of small passages sensitive to dirt, though. If you opt to open them up, put in new gaskets. They won't seal internally with the old gaskets, and give you grief you can't imagine. In other words, don't compound the problem with half-hearted service.

The hard starting could be from fuel delivery problems, or it could be from serious engine damage from the overheating. Don't mess around. Check compression, and find the problem before you run it.

hope it helps
John

 

[84Ranger]

Re: Mercury over heating

I think I found the poppit valve but not sure......it in the right side of the motor if your looking at it from the back...starter side....on the bottom of the right block. It a round housing and has two screw and a little hole like on the water pump on a car. It seem to be leaking a little from it at time..has residue. I took it off and did not see any gasket but I did see like a big round rubber screw in with a small screw in the middle. Is that the poppit valve and how can I tell if it is bad.

I took all the carb apart and clean all of it really good and installed new gasket. Look at it again and like you said there is no adjusting screw or anything that can be adjust. So I should install a in line fuel filter.

I don't think the water pressure step back at all....never really look at that...that's a good idea...will the poppit valve operate on just high rpm...cause I can run it in high rpm (not in gear)about 3 to 4,000 rpm the water pressure is reading a pretty high....I have a water tank that I soak the motor in and was just thinking if I can get it to step back without going into gear.

 

[hkeiner]

Re: Mercury over heating

The below information might be helpful if you want to further troubleshoot the cooling system.

 

[gss036]

Re: Mercury over heating

Follow the about instructions. If there is water leaking out of the bleed hole, the diaphram pobably has a small hole in and does not open properly. You should only be reading about 12 pis at WOT.

 

[84Ranger]

Re: Mercury over heating

Thanks again guys.......I will inspect and follow as the chart applys. I finally found the poppit valve and took it apart and it has alot of corrosion as to dirt and bulid up around the poppit valve.

How can u tell if the poppit valve is bad.....how much force does it take to push the poppit out..... mine take some force to push out the poppit valve. Oh what pushes the poppit valve out...is it water pressure or temp like t-stat?

The water flow chart says that water exit through two 1/8 holes in the lower adaptor plate into the exhaust....can I see those hole from the outside or do I have to remove something to see the holes?

thanks