Super Technical Knock Sensor Quest

Tom G · December 25, 2016

If I can get this super specific piece of information from somebody then I'll share this idea that hit me like a ton of bricks the other day. Maybe the answer to the question is why nobody does it.

Vortec v8 6.0 on a 2500 GMC.

What is the temperature that the knock sensors reach? I would tell you where they are but someone who knows that answer probably already knows exactly where an internal holding place for a knock sensor would be.

Thanks up Ya'll

Dnt · December 25, 2016

Are you concerned about what sealant to use to keep moisture from affecting the knock sensor? Typical RTV Red is good for 600f and that should work for you. Moisture intrusion is a common issue on late model knock sensors. How many times have you pulled the intake off already? OEM only on the replacement sensors it costs more but prevents some extra work to replace later. Good Luck

Daryl LBZ · December 26, 2016

I used black rtv on mine, but I don't spray my engine down either so it's not necessarily something I needed to do. Just some insurance.

Tom G · December 26, 2016

I know all about the RTV fix. I have a different idea. I need to know what temperature that area gets to if it heats up at all?

kstruckcountry · December 26, 2016

Around 400 tops I'd bet.

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Tom G · December 26, 2016

Around 400 tops I'd bet.

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Here is my idea: It is very simple. Maybe it's a bad idea.

Instead of the RTV fix, or in conjunction with RTV (mainly because of the hole that they instruct with it) To carefully cover all the metal on the sensor in Rust Inhibitor spray before installing it.

Problem: The rust inhibitor that I have says to not use on surfaces that will heat to over 120 degrees fahrenheit.

davester · December 27, 2016

Yeah, I don't think that is a good idea. When I did my '04 Sierra, the engine pretty much never was washed (it's a work truck), so neither sensor had any significant rust. I still did the RTV dam when I put in the new sensors/harness.

Just doing the RTV dam should be more than fine to prevent any significant mount of water from entering those two holes, even if you do wash your engine regularly.

kstruckcountry · December 27, 2016

Even with the rust inhibitor, they will corrode eventually, whether you wash the engine or not. Moisture is enevitable. My vote is for tons of sealant, haha.

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Tom G · December 27, 2016

Even with the rust inhibitor, they will corrode eventually, whether you wash the engine or not. Moisture is enevitable. My vote is for tons of sealant, haha.

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I used black rtv on mine, but I don't spray my engine down either so it's not necessarily something I needed to do. Just some insurance.

Are you concerned about what sealant to use to keep moisture from affecting the knock sensor? Typical RTV Red is good for 600f and that should work for you. Moisture intrusion is a common issue on late model knock sensors. How many times have you pulled the intake off already? OEM only on the replacement sensors it costs more but prevents some extra work to replace later. Good Luck

I notice you guys are RTV'ing the seal completely. I was thinking that it would aggravate engine performance or the functionality of the piezoelectric crystal.

Tom G · December 27, 2016

Also, does anyone else have a stab at the top temperature those sensors get to? The engine runs at a cool 240 if it is operating as it should.

Tom G · December 30, 2016

Can anybody say what a difference the full circle as opposed to the half moon shape has made if any?

carkhz316 · December 30, 2016

Can anybody say what a difference the full circle as opposed to the half moon shape has made if any?

That contrary to what GM says, it has worked better to prevent ingress of moisture (RTV all the way around) vs leaving an airgap to let moisture evaporate out. Of the dozen or so trucks I've fixed/ replaced KS on, I've sealed all the way around with zero issues. I mean, isn't that what the rubber plug/ seal is trying to do; seal it up completely? If GM's method were true and effective, they would leave a cut-out of the rubber plug itself.

Daryl LBZ · December 30, 2016

That contrary to what GM says, it has worked better to prevent ingress of moisture (RTV all the way around) vs leaving an airgap to let moisture evaporate out.

Funny how that works isn't it. Most people try and say the manufacturers way is always the best, well in my opinion not always.

MrCat63 · January 9, 2017

I notice you guys are RTV'ing the seal completely. I was thinking that it would aggravate engine performance or the functionality of the piezoelectric crystal.

Since there is no mechanical connection between the cap and the knock sensor I don't think the RTV would affect the sensor's operation. The cap is there as a moisture seal and wire guide. The sealant will not act as a dampener.