Knock sensor

[CradGen2]

Reading the owner’s manual on the boat to drain the block. I haven't winterized a boat in several years and I have never winterized a GM motor. I have to 2 knock sensors what do they do.

Sorry not an engine GREEK, so I’m clueless. I know enough to be dangerous and get the water out of it.

From the looks of them I can't imagine they they are there. I assume my car has them now too? Trust me I have NEVER lifted the hood on that. Company car so no need.

[DanielC]

RE: Knock sensor

The two knock sensors let the engines computer know when the engine is knocking, and they retard the ignition timing to make the knock go away.
They are just screwed into holes that normally would have plugs in them on the sides of your block, below the exhaust manifolds.
When you put them back in, do not use any sealer on them, they must make electrical ground to the block.

[CradGen2]

RE: Knock sensor

Thanks I didn't use any sealer, but i did use a VERY light coat of oil to keep the metal from rusting. Should I know have done that? When I mean light coat of oil I put a little on my finger and rubbed it on the threads.?

[Nautiquehunter]

RE: Knock sensor

Engine knock or spark knock happens when the explosion inside the cylinder occurs before the ignition spark.
This can happen with low octane fuel , overheating and too high a load on the engine to name a few.
The knock sensors detect the knock and retard the timing untill the knock goes away . By doing this it saves the engine from suffering major damage such as burning a hole in a piston. On late model GM marine engines they are located on both sides of the block where the drain plugs would normally go. Just remove them to drain the block.
And yes most newer cars have them also.

[ClemsonDave]

RE: Knock sensor

That should be fine. I usually install petcocks in those spots so I can just push a lever and have them drain.

[CradGen2]

RE: Knock sensor

Clemson - So you don't use the Sensor at all?

[Nautiquehunter]

RE: Knock sensor

The sensors can be moved as long as they are mounted solidly to the block.

[ClemsonDave]

RE: Knock sensor

I still use the sensors. Just in a T fitting with the petcock.

[swc5150]

RE: Knock sensor

Dave,
Awesome idea! I'm stealing it from you!

[ClemsonDave]

RE: Knock sensor

Even better was my '03 that had a shower. I'd pull the boat out of the water then turn the shower on. It would drain 90% of the water out of the entire system.

For the heater, go to Lowe's and get some metal garden hose quick disconnects. Put them on both hoses near the block. Disconnect them and blow into one (insert joke here) and it will get the water out of the heater. Then if you want to block it off for the summer, just make up a small section of hose with the same quick disconnects. Put it in place of the hoses leading to the heater.

I got winterizing down to about a minute tops. Of course, it only stayed that way for a week or so as I ski a little during the winter.

[Quinner]

Re: RE: Knock sensor

I still use the sensors. Just in a T fitting with the petcock.

Dave,

Have a couple questions about a few things you mentioned, thought it was not recommended to put any fitting, petcock or whatever, between the knock sensor and block?

I also use my heater to partially drain my system prior to winterizing, boats now in the garage, out of curiosity I ran my shower into a bucket to see how much it drained, ended up only being about a gallon, how much water does a SBC hold?

One thing not mentioned, the knock sensor is supposed to be torqued to a specific spec when installed, 15 ft/lbs IIRC.

[ClemsonDave]

RE: Re: RE: Knock sensor

Never had a problem. Didn't do it to the '08 since I didn't ski much last winter. The fitting was only about 1" away from the block.

15 ft/lb is not much. Not sure even my 3/8" torque wrench goes that low. It's about hand tight.

Don't know how much fluid the system holds, but I'd run the shower, then open all the other points and almost no water came out. It probably depends on where it is plumbed.

[CradGen2]

RE: Re: RE: Knock sensor

My torque wrench only goes to 20/LB, so I only hand tightened. Actually I was able to back it out by hand, so figured why not put it in that way.

[slhesten]

Re: RE: Knock sensor

I still use the sensors. Just in a T fitting with the petcock.

Dave,

Have a couple questions about a few things you mentioned, thought it was not recommended to put any fitting, petcock or whatever, between the knock sensor and block?

I also use my heater to partially drain my system prior to winterizing, boats now in the garage, out of curiosity I ran my shower into a bucket to see how much it drained, ended up only being about a gallon, how much water does a SBC hold?

One thing not mentioned, the knock sensor is supposed to be torqued to a specific spec when installed, 15 ft/lbs IIRC.

I would also like to get a "final verdict" as to whether it is okay to put a T between the block and the knock sensor, with the other end of the T used for a quick drain (for winterizing)?

Why is using a T on the knock sensor discouraged? it seems like the engine knocking would easily vibrate through a brass T coupler...

[DanielC]

RE: Re: RE: Knock sensor

I would discourage putting the knock sensor on a "T" fitting. It is sensitive to vibration, and putting it on extra pieces of pipe may affect the frequency it responds to. It may make it more sensitive, or less sensitive, I do not know.