5w30 vs 5w40 for Honda K24 2.4l 320hp fully built motor that will be used for daily drives.

The Netherlands
Engine builders might be familiar with the Honda K series, a high output high revving 4 cyl engine built between 2000 and in some form still built today.

The engine:
In europe we got the civic type r, it uses an k20 (means 2 liter) block with a special better flowing head which has V-tec and VVT on the inlet camshaft.
The engine we are building uses the k24 (2.4l) shortblock from an EDM accord type S and is fitted with the K20 Type R head.

The internals consist of race cams with heavy springs, carrillo rods and 12.5.1 comp wiseco 2618 alloy fully forged pistons which means it will have cold start slap/rattle due to the expansion.

For the oil clearances we maintained the stock Honda oil clearances, we did not choose to go al little loser because it will only be used on the streets and no heavy long temr race usage. Also the Honda clearances are known to be superb an capable of revving 10.000 rpm on stock engines.

The main bearing clearance is around 0.038mm/0.0014 inch
The rod bearing clearance is 0.050mm/0.0019 inch

The engine has an water/oil heat exchanger and will probably never see extremely high engine temps. This engine has a timing chain.
It will be used for daily drives every now and then, temperatures here are between 0 and 35 degrees but i dont think the car will be used much in the winter.

The engine will redline at 8300 rpm because then the piston speed exceeds 25m/s. It should produce about 320hp out of 2.4l so that is 133 hp per liter which is more than a ferrari 458 which is the highest n/a hp per liter production car.

Stock oil recommendations:
The EDM civic type r where the head comes from was advised to use 5W40 or 10W30, however most use 5w40, which was also used in the old engine.
The EDM accord type S where the shortblock and clearance specs come from was advised to use 5w20. (the clearance specs for the k20 and k24 where almost the same)

The civic Type R was sold as an hot hatch, the accord type S as an sporty family car.

Thinner VS thicker:
The newest turbo Type r uses the k20c1 engine which produces 320hp out of a 2l turbo, it is advised to use 0w20.
The ferrari 458 which has a high revving n/a v8 is advised to use 5w40.
The older bmw M high revving v8 and v10 engines where advised to use 10w60 and had even thighter clearances, these engines where known for rod bearing failures.
I heard that modern motogp and formule 1 engines run on something like a single grade W8 oil, however those engines start already hot.

5w40 Thick oil:
- Beter extreme load bearing for better protecion under extreme conditions
- Is advised to use in the Type R and is used a lot with good results.
- Maybe a little better for the forged wisecos because the fit so lose during the cold start up.

5w30 Thin oil:
- Flows faster through the engine so is not exposed as long to the hot areas/bearings as the thicker oil, this cools beter and deteriotes the oil slower.
- Wont cavitate as quick as 5w40 does, the k20 has an extremely good flowing oil pump but cavitating of oil means that even for a short period the rod will probably seize and break. The engine will run 8300 rpm so that spins/flows pretty fast.
- Lighter engine running, maybe slightly more horespower but this is not our goal.
- Alot of k24s world wide run on 5w20 without any real problems as far as i know, also the specs from the factory where designed to use this oil.

So what do you guys think? I am not looking for brands or anything, only what viscousity you would advise and why/why not?


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What part of Europe? I may base which oil I run on ambient temps. Here in the Midwest (USA) we get quite the fluctuation of temperatures. 38°+ summers, -18° winters, at the extremes. I therefore run slightly lower viscosity during the cold months, and higher viscosity during the warmer months.

Many enthusiasts in the states also run K20/K24 hybrid engines with good results. I don't have any first hand experience with this engine, though. Will 5w30 cause any problems with VTEC actuation in the K20 head?

I think if I were in your situation, I would try to run a stout 5w30 at first, send some oil for lab analysis, and decide from there which direction to head in regards to viscosity.

Keep us posted with what happens. Sounds like a really cool build.


Thread starter
The Netherlands
What part of Europe? I may base which oil I run on ambient temps. Here in the Midwest (USA) we get quite the fluctuation of temperatures. 38°+ summers, -18° winters, at the extremes. I therefore run slightly lower viscosity during the cold months, and higher viscosity during the warmer months.
The temperatures here are between 0 and 35 degrees although i dont think it will see much usage in the winter.
5w30 cause any problems with VTEC actuation in the K20 head?
I am not sure about that, i heard some stories that some use thick oil because the vtec. But the k24 EDM has v tec and it uses 0w20 without any problems.


Down Under
With 30 grade oils (eg 5W30, 10W30, etc) there is a big difference between an ILSAC GF-5 oil with a minimum HTHS 2.9 cP and a ACEA A3/B4 or C3 oil which has a minimum HTHS of 3.5 cP. Most ILSAC 30 grades have a HTHS of about 3.0 +/- 0.1 cP

Also recall under J300, the minimum HTHS for 0W40 or 5W40 is 3.5 cP

So something like Castrol Edge 5W30 A3/B4 and Mobil 1 0W40 have effectively the same (or very close) HTHS of about 3.6 cP (sorry I haven’t got the data sheets on me right now, but I’m pretty sure this is correct from memory). They both also have about 1000 ppm ZDDP for wear protection, as opposed to ILSAC oils that typically have 700 to 800 ppm ZDDP (Phos and Zinc). I haven’t studied many C3 oils, but they appear closer to ILSAC oils when it comes to additive package.

Me ? I would run an oil that is rated A3/B4 first, and Not run and oil that is rated GF-5 (or GF-6). After that, you are splitting hairs.
Do you have access to Amsoil? I'm thinking their Dominator 10w30 would fit the bill nicely. Excellent cold flow capability, excellent film strength, high zinc. Just my opinion.
I would run a Porsche A40 and MB 229.5 oil (HTHS 3,5-4,0 cP level), which is available everywhere in Europe at reasonable prices
port injected NA engine

just use plain jane (new life) 0w40
That would work too, my preference however is the ESP lineup from XOM. "I" feel it is the best of their offerings, and at $4.99-$5.49/qt. a few times a year from NAPA I find it hard to pass on, especially when they have a rebate running. ;)


Thread starter
The Netherlands
Ok so a lot of you advise running an 0 or 5 w40 oil with a3 a4 spec.

Unfortunately amsoil and mobil are pretty expensive here in holland.
In the old engine we currently run shell/penzoil helix ultra 5w40 gtl oil with a3 a4 spec which will probably have an hths of around 3.5.

Hearing the recommendations from you guys we will probably stick with it and dont drop it to a lower grade.

We dont want to sacrafice protection for a little fuel consumption or horsepower.

All in all this engine costs between 4500 to 5000 euro to build so we dont want to throw a rod or anything.

Eventhough it is a high spec engine it wont see any track use or anything. Wide open throttle operations will only be a matter of seconds so i dont see any benefit in going to a race spec motul 300v, liqui moly or ravenol oil.

We are currently still in the building stage, after that we have to run in the engine in.

Do you guys have any recomendations?

I have looked into it but personaly dont see any benefits in using a very specific method.

Generaly manufacturers advise to drive around 600 miles in varying conditions and dont pass 5000rpm.

After that an oil change and then onto the dyno.
Munich, Germany
I was thinking the same, i am owing a Honda S2000 with the F20C engine. 9.000 RPM, high piston speed.
For this engine Honda reccomends also 10w-30 or 5w-40. The later one surprisingly for winter, below freezing point. (??)
There are reports that the S2000 engine has a higher then average Oil temperature. I dont know it.

It is correct in my opinion that you try to select a oil based on the bearing clearances. If you use -30 oil look for a oil with a HTHS over 3.5 for this high reving engines. I decided to try a thin -40 oil as best compromise and ended up using Shell Helix Ultra 5w-40. This oil is based on GTL and has a viscositiy of 12.9, it is on the borderline to a -30 Oil. It carrys a lot of good approvals.
So far, the engine runs great. It has oil consumption, i maybe try a different oil, but so far i am satisfied with it.
Do short OCIs and change the oil often because of the high piston speed and maybe high oil temperatrues.

Because of the high piston speeds and RPMs i am a little bit hesitant about the use of 0w-40 in these engines. 🤔 I am concernd that this oils shear quickly.

BTW, in the german S2000 Forum some "Experts" try to convince people to use 5w-50 oil. This year where 2 damaged engines reported, both engines sufferd rod bearing failure after hard use on the autobahn. Both engiens where filled with 5w-50 oil.