E39 525i Guidance needed re engine

[Imraan Adam]

Hi All
I have a 525i touring (M54B25) and had some engine trouble.
The original engine overheated and I got it repaired but 250km's later she overheated again. So I ripped it out and then decided to purchase a used engine from an engine importer and install it. It worked well for 2 years and now I picked up a misfire losing compression in cylinder 4 and 5.
I really want to keep the car as it is still in a good condition and need some advice on what to do?
Do I attempt to rebuild the original motor AGAIN?
Do I repair the current engine?
Do I buy another import engine?

 

[Rotinaj]

chuck in another used engine, but before you do, strip it and change the headgasket and sort your cooling system. Rebuilding is not worth it.

 

[Imraan Adam]

I am also leaning toward another used engine. I think I will start hunting soon.
When you say sort the cooling system. What do you suggest? All my components are new. I just don't trust the Viscous clutch set up and would prefer an electric fan set up.

 

[Rotinaj]

I am also leaning toward another used engine. I think I will start hunting soon.
When you say sort the cooling system. What do you suggest? All my components are new. I just don't trust the Viscous clutch set up and would prefer an electric fan set up.

Viscus works fine.  

Are your hoses all fresh? 
Is the radiator free of sealant and other nasty things.
Expansion tank fine?
Coolant Cap sealing properly? 
Waterpump and Thermostat fine. 

M54 engines don't just lose compression most common killer is lack of oil changes and buggered heat gaskets due to cooling issues.  My highest millage M54 was at 360 000km and ran virtuall equal compression over all 6, 133psi +-1.

 

[Imraan Adam]

Hoses are good.
Radiator is new (silverton BEHR)
expansion tank new (Goldwagen)
coolant cap new. (Goldwagen)
water pump new (agent)
Thermostat new (Goldwagen)

I spent alot on her in this few years but love her.

 

[Rotinaj]

Hoses are good.
Radiator is new (silverton BEHR)
expansion tank new (Goldwagen)
coolant cap new. (Goldwagen)
water pump new (agent)
Thermostat new (Goldwagen)

I spent alot on her in this few years but love her.

Start there and get OEM.

 

[Imraan Adam]

Thanks alot for your response. I take your advice.

 

[wilnic]

Also see if you can install a thermostat that opens sooner ie lower degrees.