The cause of noisy engine is in an unexpected place! What is the cause of the noise that reduces even fuel efficiency?

If you have a noisy Delica Space Gear and you’re wondering why it doesn’t get quieter even after using fuel and oil additives, it might be worth a try.

I replaced the fan belt and pulley bearings, which don’t seem to have much to do with the quietness of the engine, and it became very quiet.

The diesel noise (squeaky noise) was loud.

The “squeaky noise” at idling was noisy to begin with.

When I replaced the fan belt, it was reduced and thinned out early in the Warri, and I felt like the ・・・・ fan belt was wearing out fast.


When I touched the pulley when I changed the fan belt for the second time, I found ・・・・・・

It’s not working!

So I hurriedly replaced the tension pulley bearings in the compressor belt and all three fan belts…

Suddenly the engine is quiet!

I’ve become so accustomed to noisy idling that I didn’t realize how quiet this engine was: ・・・・

I didn’t know that.

Basically a quiet engine.

When the 4M40 was developed, it was supposed to be a dramatically quieter engine with dramatically less black smoke.

It’s hard to believe with the state of the 1st model 4M40.

But when you’re driving, the engine is so “quiet” that you can’t imagine how quiet it is at idle.

So the problem is when it’s idling.

You can’t do that with just an oil additive.


Everyone tries various oil additives, thinking “I wish it was easier to make the engine quiet”.

How does that work?

It’s quiet! But that additive is probably added with the new oil when you change the oil, right?

I used to question the performance of the additive and tried changing the oil without the additive and using only cheap multi-grade (10W-30) oil. Then

It still sounds better and quieter with only cheap new oil than pre-replacement oil with additives!

How about throwing in an additive when the engine noise starts to get too loud?

I even thought about it and put in an additive before changing the oil. But I didn’t see a dramatic change.

Maybe the fact that it felt quieter when I used the additive was an effect of the new oil after all.

What is the nature of the noisy engine noise after all?

The sound of an engine, especially a diesel engine when idling, contains many different sounds. For example

  1. Sounds from the cylinder head such as tappets and camshafts
  2. Sounds from the engine block such as connecting rods and crankshaft
  3. Knocking and combustion noises (called “kara-koro”)
  4. Noise from the bearings of the engine itself or the rotating shaft of auxiliary equipment
  5. Frictional noise from fan belts, etc.

If you listen carefully to the engine sound with your ears near the radiator grill, you will find that it is surprisingly quiet except for the ・・・・ rattling sound.

Oil additives may have an effect on 1, 2, and 3.

But 1 and 2 are not that loud to begin with.

3 is a sound that is the fate of diesel engines and cannot be eliminated.

If you think about it calmly, the sound is quiet and it is not supposed to disappear, so even if you add oil additives, it will only change the tone and not physically change that much. I think…

I think so.

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Pulleys and fan belts, sir.

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The pulley bearings and the fan belt have been replaced, and as a result, the engine is much quieter.

As a result, I feel that the engine has become much quieter.

The pulley bearings in particular had been bad for quite some time. The bearings that I replaced looked fine on the outside, but they were so bad that I couldn’t turn them by hand.

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Since I was forcing myself to turn such a thing, it must have made a lot of noise and the belt must have worn out.

I guess the source of the noise was the pulley “bearing”.

A new fan belt is also good. If you listen to the sound around the radiator grill, you can hear it.


It sounds like the gasoline engine of a luxury car!

Changing the coolant also helps!

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I changed the coolant about two years ago, and after the change, I felt that the idling sound became quieter.

Coolant has anti-freezing and anti-corrosion effects, as well as a lubricating effect. This lubricating effect may be used to keep the water pump running smoothly.

However, when coolant gets old, its anti-freezing, anti-corrosion, and lubricating effects all fade away, and the coolant may freeze or rust on a very cold morning, causing the coolant to become sloppy and clogged, or the water pump bearings may be damaged and need to be replaced.

It is recommended to change the coolant every four years or so.

My mileage is now over 315,000 km, but the water pump has never been replaced and there are no strange bearing noises.

The fact that I have not had to replace the water pump for such a long time without any strange noises may be due to the regular coolant replacement. I think it’s thanks to regular coolant changes.

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After all, what is the best way to silence a noisy engine?

  1. Pulley bearing replacement
  2. Fan belt replacement
  3. coolant replacement

I think that if you take care of all of these things at once, the engine will be quieter and you can expect better fuel economy. ・・・・・ At least

Oil Additives

I think you can reach a realm that cannot be surpassed by oil additives alone.

Fan belt replacement

Pulley bearing replacement

As for oil additives, I don’t know if I need to use them or not. I think so.

If you want to use a good oil additive, it will be quite expensive, and I personally think it is more beneficial to change the cheap oil at an early timing (around 2000km). I think it would be more beneficial to change the oil at an early stage (around 2000km).

When are fuel and oil additives effective?

The light knocking sound that diesel engines make while idling is unavoidable due to the way they work.

However, if the rattle during idling is too loud, or if you hear a rattling sound during acceleration, you may be experiencing abnormal combustion (knocking) and need to take countermeasures.

The main causes of abnormal combustion are

  1. The oil is burning together with the engine oil.
  2. Soot accumulation in the combustion chamber.
  3. Injectors are dirty.
  4. Normal compression pressure is not obtained due to age-related deterioration.

In the case of 1, smoke comes out from the muffler or blow-by oil accumulates if you have an oil catch tank.

Fuel additive will help with the second and third problems. After adding the additives, do not refuel until the fuel tank is empty. If you drive 500km to 1000km with fuel additives, you will not need additives for a while.

It would be good to mix Wacos EPS or Forediesel with the oil at the time of oil change. It will improve the airtightness of the cylinder.

Super important! Late model 4M40 must have power supply checked!

The late model 4M40 engine is electronically controlled, so if the electricity is weak

  1. Engine power is not so good
  2. INVECS II does not work well
  3. Blow-by oil increases
  4. Engine starting is not good.
  5. Increased engine noise (knocking) both while stopped and while driving

Symptoms such as In the case of late model 4M40, it is better to check the battery and terminals before using additives to deal with increased engine noise and knocking sound.

Just connect the battery terminals properly, and you will be in great shape.

If the knocking noise is loud

If you have checked the battery, terminals, wiring, alternator voltage, glow plugs, connection plates and contacts, etc., and the knocking noise is still loud when the engine starts or when the engine is fully warmed up, you may need to have the car checked at a repair shop.

The car’s ECU (engine computer) keeps a record of problems, and the repair shop has a machine that can read it. This may indicate a problem with the sensors.


If you want to make your engine quieter

  • Pulley bearing replacement
  • Fan belt replacement
  • Coolant replacement
  • Battery and terminal check for late 4M40
  • Fuel additives and oil rise and oil drop preventive

I guess that’s about it. Once you’ve done all this, I don’t think you need any more oil additives or fuel additives. I am basically a

“I don’t use additives”.

Correction (4/8/2018), by all means use excellent oil additives (lol).

It will change!