diesel engine knock on cold start goes away after like 3 minutes

[somerandomguy1]

good morning,

1990 toyota corolla diesel, on cold startup the engine knocks very loudly to the point the the whole car is rythmically swaying in harmony with the engine knocks, goes away after 3 minutes, sometimes goes away after a minute of half. never happens when engine is hot, only on cold startup when engine is absolutely cold. i will post video at a later time of the knock.

thanks

 

[blufeb95]

I don't know these engines, but sounds like maybe the engine mounts are wore out, if they're hydraulic eventually they'll leak oil over time and when they're cold they'll allow the engine to knock around but once they warm up they'll build more pressure and absorb the shock again, if they're viscous rubber, the rubber can turn hard with age and when they're cold they'll be hard as a rock and transfer all vibration to the car but as the rubber warms up it'll become more pliable again and absorb the vibration of the motor.

 

[Pelican]

All diesels "Knock" but such a movement in a car that is 30 years old would indicate, as blufeb95 said, worned out motor mounts

 

[65f100]

I've got a 1958 diesel tractor with an exhaust manifold leak. It sounds terrible until it warms up, at which point the exhaust no longer leaks.

 

[Greasymechtech]

So, after 3 minutes, the motor mounts are good again?

Are you sure its starting on all cylinders?

After you inspect the mounts, need to make sure all cylinders, when cold, are getting fuel and glow

 

[wwillson]

The loud knock is common with cold diesel starts when autoignition is delayed. When ignition is delayed, but does happen, it tends to happen very rapidly, which is the knock you hear when the pressure wave hits the piston, head, and cylinder walls. If you increase the cetane, it will make the fuel easier to ignite and reduce the cold startup clatter. More cetane is better for diesels.

In this case a poorly atomizing injector could be making the clatter worse.

 

[somerandomguy1]

A couple of mechanics told me that some of motor mounts are shot and needs replacing. The mounts mounts are rubber.

I also have added two stroke oil to the diesel to the last two tanks of diesel. I have read online that two stroke oil lowers the cetane.

I had the injectors recalibrated and new inyector nozzles installed less than 10k miles ago.

 

[wpod]

What is the compression of the each of the 4 cylinders? You have been chasing this problem for a while?

 

[wwillson]

I have read online that two stroke oil lowers the cetane.

Why would lowering cetane be a good thing?

 

[somerandomguy1]

I dont intentionally lower the cetane it seems to be a byproduct of adding two stroke oil for increased lubricity of the fuel pump and cleansing of engine.

I dont know the compression value in psi for each cylinder. A couple of mechanics told me the engine has good compression. I noticed the problem about a couple of weeks ago maybe.


4 options possible in order of likelihood:

1) the motor mounts. The rubber motor mounts are shot. I have been running 60 psi in tires since maybe a month ago. The higher psi tires affect the suspension and this could of have accelrrated the wear on the engine mounts that were already shot.

2) the cetane value. I added two stroke oil to the diesel to the tank and this lowers cetane.

3) fuel pump. It doesnt pump the two stroke oil well with diesel until the fuel pump heats up and this fuel starvation causes the knock. I have noticed the tailpipe smokes for the three minutes when starting up and the stops smoking.

4) the glow plugs arent heating properly and starts are rough because of this.

 

[wwillson]

2) the cetane value. I added two stroke oil to the diesel to the tank and this lowers cetane.

How does the two stroke oil lower cetane, unless you are putting is a LOT of two stroke oil?

3) fuel pump. It doesn't pump the two stroke oil well with diesel until the fuel pump heats up and this fuel starvation causes the knock.

Are you putting in that much two stroke oil that it thickens the fuel at low temperatures?

4) the glow plugs aren't heating properly and starts are rough because of this.

That will certainly cause rough or no starts.

 

[somerandomguy1]

I put in about 250 ml of two stroke oil before i fill up the 50 liter tank. I read in other online forums that 250 ml 2s oil per 50 liter diesel is the ratio for mixing two stroke.

Where i live in nicaragua, in the morning it would be at the coldest around 78 degrees fahrenheit.

Maybe i could check the glow plugs somehow?

 

[kschachn]

I am confused as to why you are adding anything to the diesel fuel in the first place. Didn’t you say that the fuel there in Nicaragua is a high sulfur fuel? It seems to me you’re potentially gumming things up with the unnecessary additive.

 

[somerandomguy1]

https://bobistheoilguy.com/forums/t...-sulfur-diesel-good-idea.338622/#post-5721775

 

[wwillson]

I can't imagine the two stroke oil is giving your fuel system or engine any benefit whatsoever.

 

[mk378]

You don't need the glow plugs in a tropical climate.

What is the theory behind 60 psi in the tires? If they don't simply blow out, you will have worse handling and shake the suspension to death.

 

[somerandomguy1]

60 psi better fuel economy.

 

[kschachn]

60 psi better fuel economy.

Which was apparently offset by having to purchase all new engine mounts.

 

[Motu]

White smoke ? These things won't start cold without glow, you could have one or 2 out which will cause white smoke until it warms up. Running ragged while cold is pretty normal too....and injection timing makes a difference too. Retarded timing will cause rough running and white smoke when cold.

 

[wwillson]

You don't need the glow plugs in a tropical climate.

On prechamber heads you will.