What makes an engine “sludge prone”?

[Elkins45]

One of the used vehicles I’m researching is a Lexus RX300 which has the 1MZ-FE engine. The Wikipedia article about this engine says:

“These engines are prone to oil gelling. Another name for the issue was "engine sludge". There was a class action lawsuit due to this problem. It is very important to the life of these engines that oil changes are done on a regular basis.”​

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What makes one particular engine more prone to sludge than another?

 

[cptbarkey]

Poor PCV valve placement and routing by the engineers. The 'ole sludge bucket 2.7L dodge also comes to memory having a similar sludge issue.

 

[supton]

IIRC, back then Toyota was moving towards 7,500 mile OCI's but with conventional oils. While having engines run yet hotter. Now multiple that by the number of owners who think maintenance is optional (or not required since it's a yoda) and now that engine is cursed. The 5S-FE was sold alongside it and it too gained the same reputation, albeit not as bad; but I think in its earlier years it may have had an oil-coolant heat exchanger that was dropped off at some point. Less control over peak engine oil temps? am guessing that didn't help either.

That's for the 1MZ-FE. Other manufactures, YMMV as to causes.

 

[MolaKule]

One of the used vehicles I’m researching is a Lexus RX300 which has the 1MZ-FE engine. The Wikipedia article about this engine says:

“These engines are prone to oil gelling. Another name for the issue was "engine sludge". There was a class action lawsuit due to this problem. It is very important to the life of these engines that oil changes are done on a regular basis.”​

​

What makes one particular engine more prone to sludge than another?

Many engine design factors such as insufficient coolant flow around piston bores, too small a radiator or fan, insufficient oil cooling on the underside of the pistons, low oil pan capacity, too long oil change intervals, etc.

 

[slacktide_bitog]

In the case of the 1MZ-FE, they made the oil passages smaller starting in 97.

 

[dfarr67]

Short trips.

 

[02SE]

IIRC, back then Toyota was moving towards 7,500 mile OCI's but with conventional oils. While having engines run yet hotter. Now multiple that by the number of owners who think maintenance is optional (or not required since it's a yoda) and now that engine is cursed. The 5S-FE was sold alongside it and it too gained the same reputation, albeit not as bad; but I think in its earlier years it may have had an oil-coolant heat exchanger that was dropped off at some point. Less control over peak engine oil temps? am guessing that didn't help either.

That's for the 1MZ-FE. Other manufactures, YMMV as to causes.

I'd say it was almost exclusively owner neglect. Working at a Toyota dealer and seeing those neglected cars come in was common. Leasing became very popular in that time frame, Toyota had a sterling reputation for reliability, and frequently people literally never changed the oil.

A car would come in with 40k+ miles, that had never had an oil change. Surprise, the oil (what was left of it) had turned to sludge.

 

[PF52]

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What makes one particular engine more prone to sludge than another?

The Toyota logo on the valve cover.

 

[Allaneddie]

I'd say it was almost exclusively owner neglect. Working at a Toyota dealer and seeing those neglected cars come in was common. Leasing became very popular in that time frame, Toyota had a sterling reputation for reliability, and frequently people literally never changed the oil.

A car would come in with 40k+ miles, that had never had an oil change. Surprise, the oil (what was left of it) had turned to sludge.

Vehicle abuse! Should be reported to the authorities and help that poor vehicle find some foster owners,

 

[BMWTurboDzl]

Vehicle abuse! Should be reported to the authorities and help that poor vehicle find some foster owners,

Automakers are loathe to charge the leasee for this sort of thing because the customer always re-leases.