Mercruiser 470 Solenoid

[emmurphy50]

Hi All,

I had a problem on vacation with my solenoid on my 1981 Mercruiser 470, which I recently replaced, sticking on and off. A few times it would not start, and more than once it locked the starter on, and would not shut off with the key and kept the starter spinning, even with the key off (and engine still ran). I checked my voltages around the system and replaced the key (since the solenoid was replaced) and all seems OK otherwise. Only think I can think of - is there a side of the switch ignition posts that must be switch and must be ignition? I have the wire to the switch on the left (looking at the posts) and the wire to the coil on the right. Any reasons why it might be misbehaving, other than I should not order solenoids on ebay? 1981 did not have a solenoid on the starter, this is the only one.

Thanks,
Ed

 

[stonyloam]

Without a solenoid on the starter you are drawing a lot of current through that solenoid. Could be that the heavy contacts are arcing and sticking. Was this a aftermarket solenoid or OEM Mercruiser?

Yeah looked that up on e Bay, I suspect that you could get away with a aftermarket solenoid IF you were using it as a slave solenoid with a starter that had a solenoid, but that it might not be up to handling the current draw with your starter.

 

[biggjimm]

My solenoid posts are marked with an "S" & "I" but my solenoid is a different style then what the book shows for your 470. I have a 76 3.0L 140. It also shows your starter as having a solenoid on it so I'll have to leave that up to the experts. It shows Sierra part # 18-5801 as your starter. Did mercruiser use somebody else's starter on this motor or is it their own starter as well?

 

[stonyloam]

Here is the diagram: https://www.mercruiserparts.com/Show...Wiring+Harness the original 470's had a starter with no starter mounted solenoid. All of the starter current passes through what later became the slave on newer models. So they used a heavier duty solenoid than 3.0's. Most folks replace the older style starters with the newer starters with a solenoid when the time comes for replacement, and use the original block mounted solenoid as a slave.

 

[emmurphy50]

The parts diagram doesn't tell me what site is the "S" and "I" on the solenoid.

 

[emmurphy50]

Without a solenoid on the starter you are drawing a lot of current through that solenoid. Could be that the heavy contacts are arcing and sticking. Was this a aftermarket solenoid or OEM Mercruiser?

It's an aftermarket solenoid... my concern is all the OEM solenoids I found had manufacture dates on the label in the early 2000's... it sticks both on and off.

 

[emmurphy50]

My solenoid posts are marked with an "S" & "I" but my solenoid is a different style then what the book shows for your 470. I have a 76 3.0L 140. It also shows your starter as having a solenoid on it so I'll have to leave that up to the experts. It shows Sierra part # 18-5801 as your starter. Did mercruiser use somebody else's starter on this motor or is it their own starter as well?

The current starter which is now called OEM as Merc doesn't sell their starter is made by ARCO.

 

[stonyloam]

OK so sometimes it does not engage the starter and sometimes when the starter does engage it sticks on, correct? If it clicks but does not start, then I would suspect that the heavy duty contacts are faulty. They are making poor contact when they close and you are getting no current flow (sometime) and when they do make contact they are getting hot (from the poor contact) and sticking together. Just as a check of the ignition switch measure the voltage on the small terminal (yellowing/red wire) from the ignition switch. It should have voltage on it only when the key is turned to "start". If the key is released, the voltage drops to 0 and the starter keeps cranking then you can be pretty sure it is the solenoid.

 

[emmurphy50]

Stony - thanks for the input - my thoughts as well. Wondering if that based on this solenoid being originally used in 1981-1982 as the main solenoid for the starter to later being converted to a slave, that modern updates to it and equivalencies can't take the current from the starter (cranking on a high compression engine?)

 

[emmurphy50]

...and since it is not labelled just want to check that the starter wire is left small post and 12V to coil is right small post.

 

[stonyloam]

I am not sure on the left/ right, but if you turn the key to "on" you should see voltage on the wire to the coil, feeding back through the wire. That wire is on a normally open switch that closes when you hit " start". So if you had it wrong the starter would start turning as soon you turned the switch to on. Also if you measure the resistance ( with wires off) the coil terminal would read open and the start terminal would show continuity with some small resistance.

 

[stonyloam]

Yeah, I think the aftermarket solenoids may not be up to the job. Probably only two choices, go with an OEM selonoid (I don't think the manufacturing date is important), or go with a new starter and use your current one as a slave, and hope it does not stick. For about 100 bucks you can gat a permanent magnet gear reduction starter for a 470 on e-bay.

 

[nola mike]

If it's operating as a slave, it should take less current. Small posts are interchangeable with each other, large posts are likewise interchangeable.

 

[stonyloam]

If it's operating as a slave, it should take less current. Small posts are interchangeable with each other, large posts are likewise interchangeable.

Small posts are NOT interchangeable. One (from ignition) activates the solenoid coil and the other (to coil) is normally open. The small posts MAY be interchangeable on a 3.0 solenoid, but not on a 470.

 

[nola mike]

Admittedly don't know the specifics of a470 solenoid, but in general competing a circuit between the small terminals induces an em field that then connects the 2 larger terminals. Not sure what you mean by normally open. Do you have a diagram?

 

[stonyloam]

The 470 uses what is called a switching solenoid.it has 4 terminals and is grounded through the case. contact one activates the solenoid electromagnet when the ignition switch is turned to start. Current flows through the terminal through the coil to ground through the solenoid case. contact two is normally open (off) and when the solenoid activates it closes and sends voltage to the coil (resistance wire bylpass). terminal three (red wire) large terminal on top has 12 v from the battery. Terminal four is normally open and closes when the solenoid activates sending voltage to the starter, either the starter motor, or starter solenoid. On a 3.0 type solenoid small terminal one is start and terminal 2 is ground. three and four are the same. The resistance wire bypass is from the solenoid on the starter.