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Engine guides and mods

451 54BHP CDI Losing Coolant

Modification Details

54BHP 451 Fortwo Diesel - Losing Coolant

As of early 2015, this became a common problem that will affect all 54bhp 451 diesels eventually.
The 54bhp diesel 451 was the October 2009 onwards model with the DPF (diesel particulate filter).


This is an issue that you will want to get fixed as soon as possible.


You may (if you check like you are supposed to) notice that the coolant is going down.
Instead of being at the maximum mark were it almost certainly was previously...

...the coolant could be dangerously low.

If you aren't the sort of person who performs the proper check ups on their car, the 1st you may know about it
is the heater is cold. Soon after that, the engine will over heat. If you keep driving, it will damage the engine.

However, you won't have noticed any water pouring out from under the car anywhere, so where is the leak?

Depending on how advanced this problem is, you may notice more white smoke coming from
the exhaust than normal or it could be running really badly and having problems ticking over.

What's The Problem?

It's a failed part. A part that can cause engine destruction in 2 separate ways if you ignore it.

The problem is with the EGR charge cooler. This part can be seen below.
It cools the recirculated exhaust gas before it is pushed back into the engine.

Essentially it's a water jacket surrounding internal pipes. The direction of the recirculated exhaust gas
can be sent 1 of 2 ways. Through 1 larger pipe on 1 side or several small pipes on the other side.

A vacuum operated flap at the top of the unit closes 1 side off to force the air through the opposite side.
If the air passes through the larger tube, it is cooled less. If the air passes through the collection of smaller
tubes, it cools more. Engine coolant flows around the outside of these pipes in a sealed jacket.

Problem is, they are badly made and the pressure of the coolant soon causes a leak inside the unit.

Here I have attached it inline to a garden hose. The water should pass in 1 side and out the other.
It certainly shouldn't be pouring out of the gas inlet hole like it is here.

The photo below is hard to make out but you can see a fine spray coming from the hole.

So you have a 2 stage issue. You can either run out of coolant and over heat the engine or you
can carry on allowing the coolant to get pushed into the engine which increases compression.
As I'm sure you know already, diesel engines are already running a high compression.

Increasing it more (depending on the leak flow rate) could blow a piston seal, head gasket or even
hydrolock the engine which could cause irrepairable damage to the con rods and pistons.


4 bolts at the top, 2 bolts at the bottom and 1 vacuum hose.
The problem is, access to this part is a pain. You can barely see it.
Part number to take to smart is A660 140 03 75.

Here is the removal procedure but you might want to bypass it instead.

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