How common is a dropped valve seat and what can I do to avoid it ? - JeepForum.com
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post #1 of 21 Old 06-10-2021, 02:08 AM Thread Starter
Rylxmp
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Thumbs up How common is a dropped valve seat and what can I do to avoid it ?

Hi guys, I have a 2003 Jeep Grand Cherokee with the 4.7 HO on 179k miles now, I was lurking through these fourms and saw quite a few horror stories about people having their engines self destruct when it decides to drop a valve seat. I read that its usually from over-heating and sometimes it just randomly happens. What concerns me is that the PO replaced the head gaskets on my jeep around 4 years ago (140k-150k miles mark). I really like my Jeep a lot and wonder if there is any truth to letting the engine sit on idle for 30ish seconds after a long drive before shutting it off will help decrease the chance of this happening. I also heard that starting it up after its still warm can cause this and if this is true ? The previous owner was a mechanic who took care of the Jeep well and I also take care of it as well. Hearing these stories causes me stress whenever I start my jeep up now and I may have to sell of my wj if this issue is common on the 4.7L. Some input on this would be great ! :Thumbs up:

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post #2 of 21 Old 06-10-2021, 09:54 AM
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When I dropped a seat it was after I got gas, drove to park it and shut it off. Came back out to start it sounds like a marble banging around. So now I always let it idle down. Whether it works or not, no clue but hopefully I don't have to find out. The theory was that you still have hot exhaust gases in the manifold and due to the iron block and aluminum heads causes the expansion and what leads to a dropped seat. So by idling it down you are allowing the hot gas to escape. As for preventive measure make sure the cooling system is working, don't let it over heat and idle down before shutting it off.

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post #3 of 21 Old 06-10-2021, 10:27 AM Thread Starter
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What cylinder did it drop a seat on and also did it throw a CEL code when it happened ??
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post #4 of 21 Old 06-10-2021, 11:45 AM
Double E
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It would have most certainly provided at least a misfire code.

Other theories (not mine) are that running the non-recommended octane can build up carbon in the combustion chamber, create hot spots and thus the valve seat drops form the heat differential.
All of the reasons may be valid, or perhaps none of them are valid.

I take my HO to redline every so often, use the highest octane I can get, add a bottle of Techron at each oil change and always keep the cooling system working properly.

So I take about every precaution I can ...let it rest a little at idle after working it hard, run the right fuel, change oil and keep it cool. That's about the best you can do really.
Many 4.7L engines you'll read about here are well-over 200K miles and haven't dropped a seat.

All that said, I might drop one tomorrow but I feel pretty good that having had 3 different 4.7L equipped WJs (own 2 now), and no dropped valve seats, I've got a decent regimen going to improve my odds.

"We have it totally under control. Itís one person coming in from China. We have it under control. Itís going to be just fine." ~D. Trump, Jan 22, 2020.
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post #5 of 21 Old 06-10-2021, 01:09 PM
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Quote:
Originally Posted by Rylxmp View Post
What cylinder did it drop a seat on and also did it throw a CEL code when it happened ??
#2 and had a misfire code with some others. I agree with what Double E says. Take care of them and they will run.

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post #6 of 21 Old 06-10-2021, 03:33 PM
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post #7 of 21 Old 06-10-2021, 08:01 PM
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I once saw a video on YouTube where a guy showed the difference Lucas fuel injector cleaner has on carbon encrusted pistons and cylinders. I ran one through a tank of gas at every fill up for nearly a year. Now I use it once or twice a month. Call it a precautionary measure.
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post #8 of 21 Old 06-10-2021, 10:48 PM
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Quote:
Originally Posted by Rylxmp View Post
Hearing these stories causes me stress whenever I start my jeep up now and I may have to sell of my wj if this issue is common on the 4.7L. Some input on this would be great ! :Thumbs up:
The problem with the valve seats on 4.7s is they are not quite tight enough in tolerance.

The engine is fine till someone overheats it once. The seat becomes unstable and then it'll fail eventually.

My engine lost a head gasket, and I caught it the very first time it misfired on start up. I removed the heads and had a reputable local machine shop change the intake valve seats for $930.

I'm confident the engine will last to 400K now.

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post #9 of 21 Old 06-11-2021, 02:23 AM Thread Starter
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Do you think that the blown head gasket that the Jeep had around 30k to 40k miles ago can still cause this ?
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post #10 of 21 Old 06-11-2021, 05:17 AM
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Quote:
Originally Posted by Jeepinpgh View Post
Yep. Often AA will have them on sale, buy one-get one.
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"We have it totally under control. Itís one person coming in from China. We have it under control. Itís going to be just fine." ~D. Trump, Jan 22, 2020.
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post #11 of 21 Old 06-11-2021, 05:21 AM
Double E
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Originally Posted by Rylxmp View Post
Do you think that the blown head gasket that the Jeep had around 30k to 40k miles ago can still cause this ?
Possible I suppose but if that blown HG occurred a few years ago, it's been running fine since the HG swap and there are plenty of miles on it since, you're probably fine but there is need to note how old the radiator is. They are known to clog up after about 8 years and need to be replaced. Good opportunity to do the WP & t-stat too.

"We have it totally under control. Itís one person coming in from China. We have it under control. Itís going to be just fine." ~D. Trump, Jan 22, 2020.
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post #12 of 21 Old 06-11-2021, 06:29 AM Thread Starter
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Sounds good, I will also look into the Techron.
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post #13 of 21 Old 06-11-2021, 07:05 AM
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yea i dont think it has as much to do with carbon. The post that said its about tolerances and during a over heat cycle the valve seats bore expands faster then the valve seat. it becomes loose and drops valve collides and game over. not like the 4.7 is a outlier in this issue..

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post #14 of 21 Old 06-11-2021, 09:49 AM
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Biggest way to keep from dropping valve seats is to watch you coolant levels religiously...there is a theory out there now(of which I agree), that the dropped seats comes from hot spots in the cooling system created by air pockets. If your cooling system stays full and no air is introduced, the hot spots cant happen. Check your coolant level weekly, and if you see a drop in coolant, fix it immediately. And make sure to do a proper bleed of the system, if repairs are required before returning it to service.(not just opening the bleed port while initial fill).

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post #15 of 21 Old 06-11-2021, 02:49 PM
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As far as I am concerned the reason(s) for dropping valve seats are pure speculation. I havent read anything from MOPAR/Chrysler that admits to these engines having this problem or what causes it. We have read about owners that have maintained their engines religiously and have sworn to never have overheated them and they still drop seats. Others have never done anything special and have not had a problem. As far as I am concerned and until I hear something definitive to me its random.
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