Starting Engine, Thumping

h3nry8888 · Dec 14, 2011

Hi all, have an issue with my Jeep Pat. 95000km 2007 FWD.

When I start the car when its cold, it is perfectly fine, sounds perfectly fine.

When the car is HOT, and I turn off and turn on within a few mins (go grab a coffee), sometimes, not all the time I hear a THUMP in the engine when starting it. Car still starts, but I doubt that can be good. Sometimes its worse than other times.

(Deep sound, not a high pitch noise, again, a low THUMP noise).

Any recommendations?
Spark Plugs changed.

5W20 Castrol Syntec every 5000km with NAPA GOLD Filter.

todde702 · Dec 14, 2011

Is it while cranking or once started? Is it possibly the AC compressor engaging? Check if the heater control is set to defrost as that will turn on the AC Compressor once running.

h3nry8888 · Dec 14, 2011

todde702 said:
Is it while cranking or once started? Is it possibly the AC compressor engaging? Check if the heater control is set to defrost as that will turn on the AC Compressor once running.

It is right after the crank when the car starts. (If you were standing and looking at the hood of the car, during the startup and the Thump persist, the whole engine nudges like someone is kicking it.

Weather Control is not set to Defrost, NO AC. (Good thinking as AC does make a low humm noise which is normal".

What else can it be?

todde702 · Dec 15, 2011

A bad motor mount maybe? Open the hood and start the engine. Have someone sit in the car with their foot firmly on the brake pedal, engine running and in drive and slowly start giving it gas. Watch the engine to see if it moves. Then repeat this only in reverse gear with the engine rocking in the reverse direction. There should be very little movement, maybe an inch or less total (between drive and reverse).

Here's what a typical bad motor mount will look like. In the video they start in drive and you see the engine move towards the firewall, and all looks good. Then they try reverse and you see the motor jump up real high. As a personal safety note though, I would not stand in front of the vehicle like this guy did while filming. Stand to the side!

MB · Jan 18, 2012

I've had that happen once on my 2010 and I couldn't get it to do it again. The only thing I did different was insert the key with the buttons facing away from me. I doubt that could have caused it though. I tried to recreate it with no avail.

cpole17 · Jan 19, 2012

Is that true about the AC compressor? Whenever the Pat is on 'defrost' for clear the front window the AC compressor is engaged??

If so why is that?

Starting Engine, Thumping

h3nry8888

todde702

h3nry8888

todde702

MB

cpole17

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