The Toyota 2JZ, Nissan RB26, and Mitsubishi 4G63 all have one thing in common, they’re known as legendary Japanese engines that everyone seemingly loves.
But, what about the engines that not everyone loves? Well, that’s what we’re looking at today. The WORST JDM engines of all time.
Preface
Okay so as a quick preface, I think it’s worth mentioning that the engines on this list aren’t all that bad.
Japanese engines are historically incredibly robust as compared to their American counterparts, and just about all of these engines have loads of potential when you fix everything bad about them.
So just keep that in mind as we go through the list. And real quick, be sure to drop a comment right below that like button letting me know what you think is the worst JDM engine of all time.
#1 Subaru EJ20/EJ25
I know the Subaru guys are going to absolutely hate me for this and vape shops nationwide will probably ban me for life, but there is absolutely no denying the Subaru EJ20 and EJ25 as one of the worst JDM engines of all time.
And I get it, the excuse is that its “just the people who drive these” and “the problems are from lack of maintenance” and while both of those excuses might be partially true, it’s hard to ignore the sea of people who have modified Subarus and had them explode, including the guys over at Donut Media.
At the end of the day, the entire design for the EJ is quite literally inspired by an airplane engine.
And if you’ve ever taken an EJ apart, you’d know that there are a crap ton of vacuum lines and hard lines everywhere, especially compared to something like a GM small block.
But, really the worst of the problems seem to lie with solely the 2.5L variant of the EJ, known as the EJ25. Now this engine came in quite a few different forms through the decades.
All in, there have been a total of 23 variations of the EJ, with some making quite a bit more power than others.
The problems start with head gasket failure, excessive oil consumption, premature turbocharger failure, difficulty tuning, and lack of lubrication in the bottom end.
Ultimately, a lot of the issues are easy to fix with a wrench and access to the internet, but the tuning difficulties, in particular, have resulted in a lot of blown-up EJs.
If you were to look at a company like Crawford, for example, they have a lot of experience working with the EJ platform and know how to get it just right to avoid potential fueling issues, which can easily result in an exploded bottom end thanks to Subaru’s use of cast pistons, but not every tuner is like that.
In fact, many tuners aren’t that good with the EJ. You could even argue the factory Subaru tune on the EJ25 is subpar, but we’re not getting that deep in this video.
Add on top of all that the famous ring land failure and you’ll begin to see why the EJ can be quite a problematic engine.
If you like working on your car regularly, the Subaru EJ might not seem that bad, but for anyone else who wants a reliable performance car, you might be better off looking elsewhere.
#2 Nissan VG30DETT
Alright, that’s enough picking on Subaru. Let’s aim our sights at Nissan. And no, not for their creation of the world-famous trumpet exhaust with the VQ, but rather their failure with the VG, and specifically, the VG30DETT.
Now this is the engine you can find under the hood of the 300ZX twin-turbo we got here in the States. You can also find this engine in two Nissan concept cars, but that’s pretty irrelevant here. This engine output a pretty decent 300hp and 283lb-ft of torque, which was a pretty good amount at the time.
Sure, the peak numbers might seem underwhelming, especially compared to something like an RB26 which has less displacement with similar power outputs, but the peak numbers only tell part of the story.
But, that really doesn’t matter because Nissan fumbled the bag pretty badly in a few key areas with the VG30DETT. The first major problem is that this engine is physically quite large and Nissan shoved it into a pretty small engine bay.
It’s absolutely terrible to work on and there is no space for anything. On top of that, it’s a pretty heavy engine thanks to Nissan’s use of an iron block, which to be fair, was pretty standard for the time.
Then there is the problem of the twin-turbo system being far more complex and problematic than it needs to be.
Now to be fair, there hadn’t been many production cars with twin-turbo V engines up until that point, so developing a perfect system was kind of out of the question. It was bound to have some amount of problems.
Nissan did what they thought was best, but it ultimately resulted in a turbo system that is quite a bit more problematic than you’d expect.
Then you have the oiling system which is known for not delivering enough oil to the bearings and specifically killing the rod bearings prematurely, part of which is probably because this engine is designed to hold just 4.3 quarts of oil, which is very very little for an engine this size with two turbos.
If you can fix the oiling system, overall, the VG30DETT isn’t actually a terrible engine, as long as you don’t mind hating your life decisions anytime you have to work in that tiny engine bay.
#3 Toyota 7M-GTE
Now I know Toyota is known for producing some of the best engines in the world both in terms of performance and reliability, but that doesn’t mean they’re perfect.
Before we got the holy grail of automotive engines, the 2JZ, Toyota had some serious learning steps with the engine before the 2J, the 7M-GTE.
Now like every other engine on the list, the 7M-GTE isn’t all that bad if you can fix its issues, but that being said, the major problem with the 7M-GTE is just that, a major problem.
What I’m talking about are the head gaskets, the head bolts, and the cylinder head itself.
During assembly, Toyota failed to torque the head bolts as tight as they should have been, but it’s just enough that it might be fine for years or even decades before the problem shows itself.
Once Toyota discovered this issue on their assembly line, they changed their assembly process and raised the torque spec for the head bolts.
But that still left thousands of these engines out there as ticking time bombs.
And because the head gasket and head lifting problem can go almost unnoticed in some cases, you can very easily end up with coolant in your oil.
This then reduces lubrication and then leads to bearing issues and for many of these engines, rod knock.
Outside the issues with the cylinder head, though, the 7M-GTE is not a bad engine at all, and although it really doesn’t compare to the 1JZ and 2JZ, it laid the groundwork those engines were built on.
#4 Nissan ZD30 Diesel
This next engine is one that I’m pretty sure 99% of you haven’t even heard of, because for some god-forsaken reason, we never got cool Japanese diesels over here in the US, and that’s the Nissan ZD30.
This little 3.0L inline-four engine powered various Nissan SUVs and pickups throughout the years, including the Navara and Patrol.
On the surface, it seems much like other JDM diesel engines, but the problems with this engine are pretty severe. So much so, that it’s often referred to as a grenade engine.
The problems start with Nissan listing an incorrect number for the oil volume, at 6 liters of oil when the engine really requires 8.3 liters of oil. Now that’s a pretty big difference and eventually, Nissan realized this issue and had dealerships fix it by adding more oil and a shorter dipstick.
On top of that, the ECU was calibrated in such a way that over-boost situations and massive boost spikes were a very real possibility, leading to loads of these engines exploding the internals.
Then there are issues with the exhaust gas recirculation system which could lead to piston failure, a mass airflow sensor that was great at getting covered in oil, and giving the ECU incorrect readings, which again, could grenade the pistons.
With all of these issues, the ZD30 has earned quite the reputation for exploding, probably more than any other Japanese engine ever.
#5 Toyota 3VZ-FE
The final engine on our list might come as a surprise because it’s yet another engine from Toyota.
Yup, not just one, but two Toyota engines on the list. I can’t wait to see the comments on this one.
The engine in question is the 3VZ-E. At first glance, it appears to be another finely crafted Toyota creation.
Designed to power the 4Runner, it marked a significant milestone as the first engine larger than a four-cylinder to grace the 4Runner’s engine bay, which was really needed with how gutless the 4Runner was with the 22R and 22RE engines.
This is a 3.0-liter single overhead cam V6, capable of producing 150 horsepower and 180 pound-feet of torque.
So, what lands it on our list of bad JDM engines? The head gaskets.
However, this head gasket issue is unique because it’s compounded by the cooling system, which is prone to trapping air bubbles and often leads to misdiagnoses as head gasket problems.
It’s worth noting that these engines also gained notoriety for being some of the leakiest power plants in Toyota’s 1990s lineup.
But like all the boomer Toyota guys say “If it’s leaking oil, there’s still oil in it.”
In all honesty, aside from the head gasket ordeal, the 3VZ-E is actually a really robust and reliable engine.