How do you test bleed system check valves?

[hkeiner]

How do you practically determine whether the bleed system check valves are functioning properly on a carbed motor?​

I generally understand that a plugged bleed system check valve can cause poor running conditions and/or starve an internal bearing of needed lubrication. My Mercury shop manual's troubleshootng guide describes malfunctioning bleeder valves as one of the possible causes for poor idle, hesitation, poor accelleration, and other poor engine running conditions. However, this cause is lumped in with over a dozen other possible causes for these symptoms. I would like to test these valves in a way that is practical and effective. The Mercury shop manual does provide instruction on how to check bleeder valves (although somewhat vague - see below) but it seems to apply to checking these valves when the motor is disassembled or the valves are removed from the block. Is there a way to test these valves for failure without removal/disassembly? I figure a failure would be if the valve is "closed" at all times (i.e., plugged up) or "open" at all times (i.e., one way flow control is not working.)​

For example,​

a) Can one test by putting a hose on the end of a check valve while installed on the motor and blow/suck through the hose by mouth with the motor off?​

b) Can one one test by using a pressure/vacuum gauge along with an air compressor to test each valve while installed on the motor and the motor off?​

c) Can one test by attaching a vacuum/pressure gauge to a bleed line (using a T-connector and adaptors) and monitoring the pressure/vacuum in the line while the motor is running?​

Any suggestion or thoughts on this would be appreciated.​

Mercury Shop Manual
------------------------------------
Check operation of bleed system check valves in
reed block housing. If valves are working
properly, air can be drawn thru check valves “one
way” only. If air can pass thru a check valve both
ways, valve is not working properly and must be
replaced.
------------------------------------------​

 

[Laddies]

Re: How do you test bleed system check valves?

To make a long story short with a bleed system diagram in hand to chart the flow thru the system with the engine running the intake end of each line will pull vacuum either with a gauge or use a finger, then with a sort piece of hose and the engine off check each ck valve to see if it operates.

 

[hkeiner]

Re: How do you test bleed system check valves?

Laddies,

Thanks so much for the reply. I think I understand the first part of your answer. That is, if there is no vacuum on the disconnected origin end of a bleeder hose attached to a check valve with the motor running, then the check valve (at the destination end of the bleeder line) is no good.

However, I don't quite understand the second part of your answer (as quoted below). Does this mean that I should blow/suck with my mouth on the hose attached to the check valve to see if the air passes through the valve in only one direction? That is, I should be able to blow through the check valve but not suck air out from the check valve?

then with a short piece of hose and the engine off check each check valve to see if it operates.

 

[Laddies]

Re: How do you test bleed system check valves?

The check valves are normally in the end of the hose that the oil residue is being drained from so that is were I remove the, for two reasons then the hose I have thats pulled off will have the vacuum in it and by hooking a fresh hose to the check valve you don't get a mouth full of crude when you suck to make sure the thing is working. Done that, been there, it tastes bad.

 

[rodbolt]

Re: How do you test bleed system check valves?

easiest way is to use a syringe and a piece of clear tubing. fill the syringe with rubbing alcohol and attach the hose to the bleed valve. push and pull lightly on the plunger. liquid should only flow one way.

 

[hkeiner]

Re: How do you test bleed system check valves?

Again, thanks for the replies to my earlier questions. I took a closer look at my Mercury shop manual and have studied the bleed system diagram (see thumbnail). The diagram does not show the direction of flow in the individual bleen lines and my boat is in storage right now so I do not have a chance to run the motor right now to check this in person.

Am I correct to understand that there is a check valve on each bleed line, that there is only one check valve on each bleed line, and that the flow within each bleed line is from the end with the check valve towards the end that does not have a check valve? The Reed Valve Leak Test diagram (see thumbnail), which I also found in my shop manual, seems to indicate that the bleed valves screwed into the crankcase push air from the crankcase into the bleed hoses. If that is the case, would not these bleed lines have pulsing pressure in them, rather than pulsing vacuum?

Also, what about the bleed lines that do not connect on either end to a crankcase location. Are these gravity fed from the high end of the bleed line to the low end of the bleed line?

Sorry for the persistent questions on this subject but I would like to pick your brains as much as you will tolerate until I fully understand this mysterious (to me) subject and can troubleshoot my bleed system properly.

 

[gss036]

Re: How do you test bleed system check valves?

I have a 1989 200 hp Merc and have never thought about checking or testing these things. How prome are they to go bad? I would think that they are just assembled with a light weight spring of some type to keep pressure one way, allowing the vaccum to suck the oil out of the reed block area, returning it to the block at the end of the lines.
What would be the most obvious symptoms of failure?

 

[Laddies]

Re: How do you test bleed system check valves?

Yes the flow goes from the ck valve end to the other end the reason for the ck is so the pulsing of the two fittings will pump the oil residue thru the line and recirculate it to keep the crankcase from loading up on oil residue with out the ck it would simply pulse back in forth in the system just like a fuel pump with a bad ck valve.

 

[hkeiner]

Re: How do you test bleed system check valves?

What would be the most obvious symptoms of failure?

It seems that the obvious symptoms of failure for the bleed check valves are the same as the obvious symptoms of many other possible problems causing poor idle and such. Following is a summary from my Mercury shop manual that lists the many possible causes of poor idle and it includes mention of the bleed hoses. Myself, I am trying to detect/troubleshoot as many of the possible causes of rough idle as I practically can, to see if I can improve the idle on my motor. That is what got me asking about the bleed system check valves. My motor is over 10 years old and I figure gummed up bleed hoses and/or check valves is a possibility.

FROM MERCURY SHOP MANUAL
-----------------------------------------
Problem: Engine Idles Rough and Stalls.
Problem: Engine Hesitates Upon Acceleration.
Problem: Engine Runs Uneven or Surges.
------------------------------------------
Possible Causes:
---------------------------------------
- Improperly mixed fuel.
- A pinched, cut or restricted fuel line.
- A dirty or restricted fuel filter.
- Low fuel pump pressure.
- An anti-siphon valve.
- A needle and seat (in carburetor) that is stuck
- Improper carburetor jets or restricted jet
- Idle mixture screw out of adjustment.
- Improper carburetor float level.
- Carburetor loose on reed block housing.
- Reed block housing loose, or gaskets are defective.
- Improperly routed or restricted bleed hose(s).
- Thermal relief valve not functioning. ​

 

[red cobia 17']

Re: How do you test bleed system check valves?

I have a 1996 225 carbed merc. and I had same problem with mine.Took it to shop and they found 5 of 6 check valves bad.replaced them and everything is good now.I talked to friends and mechanics too and there was just too many possable things that could be causing my poor running at low or slow idle.I gave up and had a pro fix it.

 

[hkeiner]

Re: How do you test bleed system check valves?

Took it to shop and they found 5 of 6 check valves bad.replaced them and everything is good now.

Yup, that is why I wanted to know how to test the check valves myself. I figure that if they go bad, it is not immediately obvious and one may endure a motor that is not running/idleing as well as possible. A "periodic" test for failure and then replacement of any failed check valves seems like a very good thing to do, if one knows how to do it simply and effectively. "Periodic" could be as often as annually or as infrequent as every 10 years.

 

[57chevyeddie]

Re: How do you test bleed system check valves?

easiest way is to use a syringe and a piece of clear tubing. fill the syringe with rubbing alcohol and attach the hose to the bleed valve. push and pull lightly on the plunger. liquid should only flow one way.

This worked great. Lead me right to the bad check valve. Awesome tip. I appreciate that.