Rehaul engine for overcompression?

germane · 01-09-2025, 11:18 AM

Appreciate any guidance please.

Its a 2011 328Xi with 156K miles, bought used and apparently was maintained well by single owner.

Coolant has been leaking since bought 18 months back and last few months, it started going dry. By the time I took it to a Indy mech last week, it was bone dry .. quite lucky. They did a check and the plug at the bottom of tha radiator had popped out. He said pressure was too high and that is also the reason for expansion tank seeping coolant. See images below

View post on imgur.com

He said changing head gasket will not help given its not the symptom and advised to do engine assembly work.. priced a used E90 engine with 90k miles for about 2.5k. Alternately, he recommended a full system chemical cleaning, drying and resealing the vaccum 500$. He said it may work for a few years but cannot guarantee.

What would you do if you were to rely on a mechanic and not DIY?

TriumphTim · 01-11-2025, 03:08 PM

I saw and replied to your other post as well.

There is silicon sealant around the drain plug hole so hard to say if "over pressure" caused fault or general plastic failure. E90 cooling systems generally last around 100k miles and then need complete overhaul.

The N51 block is pretty sturdy although running it without coolant is bad, their head gaskets don't tend to go if engine is generally maintained.

Did the shop get a thermostat fault code? From where the shop is pointing you, I don't think they are super experienced with this specific engine and chassis.

N51 is the SULEV engine which has a pricy radiator with an extra sensor and coating, which may be why yours was patched up. Or you can swap the old sensor over, see details here.

https://www.ecstuning.com/b-csf-part...718~csf/?gQT=2

If the head gasket isn't blown, what does the shop think is causing the over pressure?

I don't understand what this means - "Alternately, he recommended a full system chemical cleaning, drying and resealing the vaccum 500$"

germane · 01-13-2025, 07:22 PM

Quote:

Originally Posted by TriumphTim

I saw and replied to your other post as well.

There is silicon sealant around the drain plug hole so hard to say if "over pressure" caused fault or general plastic failure. E90 cooling systems generally last around 100k miles and then need complete overhaul. The car has 157K miles, think cooling has reached end of life?

Did the shop get a thermostat fault code? From where the shop is pointing you, I don't think they are super experienced with this specific engine and chassis. The owner has a similar 2001 3 series and they work with a lot of german cars, maybe not N51 as its not common in this state.

N51 is the SULEV engine which has a pricy radiator with an extra sensor and coating, which may be why yours was patched up. Or you can swap the old sensor over, see details here. This is useful, which I had this last week!

https://www.ecstuning.com/b-csf-part...718~csf/?gQT=2

If the head gasket isn't blown, what does the shop think is causing the over pressure? I dont know. I will admit when they answered this question earlier in the week, with their accent of English am just not able to decipher. The car is immobile 10 miles from home given it has no coolant and a plug out, so am a bit tied.

I don't understand what this means - "Alternately, he recommended a full system chemical cleaning, drying and resealing the vaccum 500$"

They finished the work and have to pick up tomorrow.

TriumphTim · 01-14-2025, 07:55 AM

Ok sounds good, let us know.

Definitely a hard place to be, steep learning curve with specific car parts and under the gun to get the car out of the shop, we have all been there!

That is why started working on my own stuff and have had two cars for years, I can flip between them, not for everyone though if you like to have a life, family, hobbies, savings, lol.

germane · 01-16-2025, 08:58 AM

Its running fine for now, will keep you all posted. The owner has an old 330i and did a similar job, he is confident it will hold.

They did
ENGINE COOLANT FLUSH
THERMOSTAT &/OR OUTLET - Remove & Replace
RADIATOR REPAIR fix the plug

They cleaned the entire thing, ensured there is no coolant and then ran the sealer. FYI.

01-09-2025, 11:18 AM	#1
germane New Member 0 Rep 12 Posts Drives: E90 Join Date: Dec 2024 Location: Washington iTrader: (0)	Rehaul engine for overcompression? Appreciate any guidance please. Its a 2011 328Xi with 156K miles, bought used and apparently was maintained well by single owner. Coolant has been leaking since bought 18 months back and last few months, it started going dry. By the time I took it to a Indy mech last week, it was bone dry .. quite lucky. They did a check and the plug at the bottom of tha radiator had popped out. He said pressure was too high and that is also the reason for expansion tank seeping coolant. See images below View post on imgur.com He said changing head gasket will not help given its not the symptom and advised to do engine assembly work.. priced a used E90 engine with 90k miles for about 2.5k. Alternately, he recommended a full system chemical cleaning, drying and resealing the vaccum 500$. He said it may work for a few years but cannot guarantee. What would you do if you were to rely on a mechanic and not DIY?
	Appreciate 0 Tweet Quote

01-11-2025, 03:08 PM	#2
TriumphTim Private 101 Rep 93 Posts Drives: 2008 328xi Join Date: Dec 2020 Location: Perkasie PA iTrader: (0)	I saw and replied to your other post as well. There is silicon sealant around the drain plug hole so hard to say if "over pressure" caused fault or general plastic failure. E90 cooling systems generally last around 100k miles and then need complete overhaul. The N51 block is pretty sturdy although running it without coolant is bad, their head gaskets don't tend to go if engine is generally maintained. Did the shop get a thermostat fault code? From where the shop is pointing you, I don't think they are super experienced with this specific engine and chassis. N51 is the SULEV engine which has a pricy radiator with an extra sensor and coating, which may be why yours was patched up. Or you can swap the old sensor over, see details here. https://www.ecstuning.com/b-csf-part...718~csf/?gQT=2 If the head gasket isn't blown, what does the shop think is causing the over pressure? I don't understand what this means - "Alternately, he recommended a full system chemical cleaning, drying and resealing the vaccum 500$"
	Appreciate 0 Quote

01-14-2025, 07:55 AM	#4
TriumphTim Private 101 Rep 93 Posts Drives: 2008 328xi Join Date: Dec 2020 Location: Perkasie PA iTrader: (0)	Ok sounds good, let us know. Definitely a hard place to be, steep learning curve with specific car parts and under the gun to get the car out of the shop, we have all been there! That is why started working on my own stuff and have had two cars for years, I can flip between them, not for everyone though if you like to have a life, family, hobbies, savings, lol.
	Appreciate 0 Quote

01-16-2025, 08:58 AM	#5
germane New Member 0 Rep 12 Posts Drives: E90 Join Date: Dec 2024 Location: Washington iTrader: (0)	Car picked up Its running fine for now, will keep you all posted. The owner has an old 330i and did a similar job, he is confident it will hold. They did ENGINE COOLANT FLUSH THERMOSTAT &/OR OUTLET - Remove & Replace RADIATOR REPAIR fix the plug They cleaned the entire thing, ensured there is no coolant and then ran the sealer. FYI.
	Appreciate 0 Quote