Warm weather startup knock?
 

Hey guys,

Wanted to get some opinions and suggestions. I've read what feels like every single post on the "typical" 3.8 cold start knock, but almost all of them pertain to colder climates / colder outside temps.

The last month or so, in the 70-90 degree days we've been having here, nearly every "cold" start (can be overnight or even just sitting for 6-8 hours) produces the start up knocking or clattering for a couple seconds. Previously, my JK only did so in the colder temps.

I run an AutoMeter oil pressure warning light (triggers between 15-18 psi) and it stays solid a good second or more at warm weather "cold" start - coincides exactly with the audible startup rattle. Used to just quickly blink as one would expect right at startup.

Thought was the anti-drainback valve in my PureOne filter (the larger length / oversized filter) was defective, so I just swapped with a Fram ToughGuard 3600 (also oversized). Same deal; no change. Both of these filters in my case worked well historically over the last number of years. In fact, after swapping the filter (yes, I did pre-fill it), the dash cluster oil can light illuminated for a second. Let it idle to check for leaks, shut it down, put my tools away and started it up again. Dash cluster light came on AGAIN for another half second. Made sure it wasn't the bulb check, as with the 2nd startup I turned the key ON first, let everything stop chiming & let the oil can light turn off, and then fired the motor (oil light was off, then back on as the motor started and idle settled, then off again).

No oddities with oil pressure while driving. Idle oil psi is usually right around 18ish PSI when fully warmed up. Jeep runs and sounds just fine anytime other than cold-motor startup.

I've been running 5w-30 synthetic for a long time, and the most recent oil change a few months ago was a blend of syn 5w-30 / 10w-30 (partially due to availability, partially to see how it would react with a slightly heavier winter/cold viscosity). The Jeep did sound a little smoother/quieter up until this warm weather startup knocking recently began, and I swear driving it the motor still sounds a tad smoother with the slightly heavier oil blend.

Could my bearings be going? Could I have got two different oil filters, both with good track records, that both have defective anti-drainback valves? Something else amiss?

'10 JK, 70,000ish miles. Ran synthetic for the last few years in it, with a 3,500-4,000 mile oil change interval (always checking / topping off oil between changes as needed).

This one really has me puzzled.

I heard it's the gas. Try premium gas. JK does not like cheap gas.

I've run the cheapest gas in my 2010 for years and 140k miles- it does not care about the quality of gas. I put premium in it because the internet says it'll make your jeep double the gas mileage and fart unicorn dust.....neither happened.

I heard that the premium gas will prevent the knocking sound. But, maybe not. I don't have my 3.8 any more. I thinking of buying a 2016 though because I miss having a jeep

still sounds like a lack of oil pressure for a few seconds. pump having to prime or something. i dont think its an issue ive had a few vehicles that rattled for a few seconds on startup and one has a little over 250k miles on it and still runs just fine.

nah... I don't buy that.

My knocks a bit on startup. Never really worried about it.

Try 0W30 synthetic if you can find it or 5W30 Amsoil.

Mine only has slight start up clack when below 0 temps with the Amsoil. Use to clack in warm weather start ups with Mobile 1. With Amsoil it can sit unstarted for a week and start up is quiet.