What tends to go bad first on an engine?

[adventureboss]

I recently had to replace the head on my Jeep 4.0 with less than 200k miles on the clock, pretty sad but I don't know what the previous owner did maintenance wise. The Wrangler was in rough shape when I'd bought it.

So anyways I was thinking, when a well maintained, not abused motor eventually goes bad at 300-400k miles, what typically fails first that necessitates a new engine or rebuild? Is it the piston rings? Valve seats/guides? Head gasket? Or is it just different motor to motor?

 

[SC Maintenance]

It’s different. Rings, cylinder taper, valves, spin a bearing, etc.

 

[PontiacHO]

On those straight sixes it’s usually the head gasket and burnt valves first. If they are ever overheated the piston rings “collapse “ and a lot of piston to cylinder scuff happens.

 

[Snagglefoot]

If we are talking generically, with some engines, it’s the accessories, pulleys, power steering pump, alternator, water pump. Then in some cases it starts to consume oil on an engine that wasn’t consuming it earlier ( worn valve guides and seals), then perhaps lifters clattering.Then the transmission will require a rebuild which is a tough one because the value of the vehicle might be less than the cost of the rebuild.

On overhead cam engines the chain(s) might get worn or the VVT system gets wonky. Eventually a valve might burn requiring pulling the head and rebuilding it. Three to 400,000 miles might require 20 to 30 years depending on how much driving you do. In the rust belt the engine might might outlive the chassis.

 

[Reggaemon]

Depends on the engine.

 

[zzyzzx]

Oil filter.

 

[FoxProTwisty]

Seals, gaskets, o-rings. Engines are leaky air pumps.

 

[emmett442]

No hard facts, but if I had to gamble, I'd say valve guides. High heat, little lubrication. If not monitored, the valve seat and face gets beat up and then you get burned valves.

 

[Hohn]

In my experience, it tends to be the vehicle that contains it.

 

[CheezWhiz]

with the 4.0 jeep specifically i think getting flipped over in a stream and ingesting a trout through the intake is the most common failure mode.

 

[spasm3]

I think the cooling system if not maintained, then that takes out the head gasket.

 

[slackinoff]

I am going to say it's motor to motor issue. There are several awesome engines that still will have very specific things that need to be addressed or they will die early. For example the 12v Cummins with the "killer dowel pin". Besides things like that, they normally will get retired from excessive oil consumption (the rings and bore wear out).

 

[addyguy]

In a lot of modern engines, it is timing chain tensioners and guides that fail and often take the chain with them. This is especially true if oil changes have been lax and the engine run low on oil.

 

[rijndael]

On those straight sixes it’s usually the head gasket

That's the first thing that came to my mind too.

 

[Strumpan_]

Rust gets the body before the engine in done here.

 

[k1xv]

If the engine gets overheated, it can weaken the head gasket. So watch for cooling system issues.

Otherwise, its valve guides and valves, then rings.

 

[Hohn]

I think the cooling system if not maintained, then that takes out the head gasket.

Or sometimes there's just a defect. Like the valley cover plate on 1UR-fe Toyotas/Lexuses. The sealant simply doesn't hold up and eventually they will leak. And of course, the typical owner, who bought a "bulletproof" Lexus, doesn't notice the coolant loss until it overheats. Bad things follow.

 

[Snagglefoot]

Maybe the title of the thread should be what tends to go bad to the extent that the owners gets rid of the vehicle. Certainly the emissions parts can go bad such that the owner is tired of repair costs. Having said that some makes are more reliable that others.

 

[ripcord]

Is your Jeep a 2000 or 2001? Some 4.0 engines in those years came with a defective casting that resulted in cracked heads.

About your question, I would say in a typical engine that's adequately maintained, the rings are what wears out first.

 

[dfarr67]

leaky seals, guides, rings, rod bearings.