B58 Coolant Loss + Rev Dip (Video)
Discussion
That is very odd. From what I’ve read about B58 coolant loss issues, a new cap cures it in the majority of cases. Both my caps are extremely tight, so hopefully when you receive your new one make a positive difference.
As to the whirring and dip in revs - I’m baffled as to what the system/engine is trying to do in that video.
As to the whirring and dip in revs - I’m baffled as to what the system/engine is trying to do in that video.
I suspect you have a hole in the secondary cooling circuit radiator, not the main coolant radiator. This is quite common on earlier cars. Later ones came with stone guards to protect the main and secondary radiators.
As well as cooling the inlet charge cooler, the secondary cooling circuit on the B58 is used to cool the aircon condenser. Most cars use an air cooled condenser, but the B58 uses a water cooled condenser.
I think the noise you can hear is probably the aircon system starting and stopping due to no cooling to the condenser. That would also explain the revs changing.
As well as cooling the inlet charge cooler, the secondary cooling circuit on the B58 is used to cool the aircon condenser. Most cars use an air cooled condenser, but the B58 uses a water cooled condenser.
I think the noise you can hear is probably the aircon system starting and stopping due to no cooling to the condenser. That would also explain the revs changing.
Old fashioned diagnostic - have you checked for damp carpets? Maybe the heater matrix is weeping a bit.
Also although I haven't looked under my M135i, I'm pretty sure it has an undertray, so if the M240i is the same, it would probably be a good idea to whip the undertray off and stick some cardboard or something underneath it to see if it's leaking on the ground.
It can only really be going one of three places - out of the car (leaky union, waterpump, burst rad etc.), into the car (heater matrix) or turned to steam (by an interface with heat, such as inside the engine via the head gasket, or into the EGR cooler if the car has one etc.)
Also although I haven't looked under my M135i, I'm pretty sure it has an undertray, so if the M240i is the same, it would probably be a good idea to whip the undertray off and stick some cardboard or something underneath it to see if it's leaking on the ground.
It can only really be going one of three places - out of the car (leaky union, waterpump, burst rad etc.), into the car (heater matrix) or turned to steam (by an interface with heat, such as inside the engine via the head gasket, or into the EGR cooler if the car has one etc.)
anonymous said:
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You mentioned that the main cooling system was pressure tested. Did they do the secondary circuit too? You could obviously have a leak anywhere on the secondary cooling circuit, but the radiator is the most likely candidate, just due to its location. Whatever happens, you need to find where the coolant is going. Like I said before, the primary function of the secondary coolant circuit is the inlet charge cooler. If you don’t have any coolant circulating, it’s ultimately going to reduce power because of high inlet air temperature. Assuming it is the radiator, I don’t think it’s a particularly difficult fix. Probably needs the bumper off, but that’s relatively simple on most BMW’s.
MarkJS said:
That is very odd. From what I’ve read about B58 coolant loss issues, a new cap cures it in the majority of cases. Both my caps are extremely tight, so hopefully when you receive your new one make a positive difference.
As to the whirring and dip in revs - I’m baffled as to what the system/engine is trying to do in that video.
My first thought / suggestion was a new filler cap too having read threads about vanishing coolant on these engines elsewhere.As to the whirring and dip in revs - I’m baffled as to what the system/engine is trying to do in that video.
anonymous said:
[redacted]
You can get the secondary radiator for about £200 if you look around. I can't see a good independent BMW specialist charging another £800 to install it. I reckon £500 all in unless you want to go to the dealer.I doubt the aircon needs to be gassed. Even if it does, it's unlikely to be linked to the low coolant level in the secondary circuit. It's possible the water to refrigerant heat exchanger has an internal leak, but extremely unlikely.
I had a similiar issue with my 2017 m240i. Weird rev drops at idle and slight rev flucuation noticeable at low speeds. Took it in to BMW who couldnt identify any issue at first but they took another look and noticed a hole in one of the radiators. It was under warranty at the time but they claimed external factors (i.e. a stone), so ended up in the middle with me paying for the part and them labour to fix it. That solved the issue.
anonymous said:
[redacted]
Yes, there’s the main engine cooling radiator in the middle and a smaller one off to one side. You can usually see it through the vents down by the fog lights. At least you can on my 340i. Replacing the smaller secondary radiator is an easier/cheaper job than the main one.
This is on a 335i, but I suspect very similar on the 240i/340i with the B58 engine.
https://youtu.be/hc1DRFqxPp0
No need to remove the bumper on the 335i. Hopefully similar on yours. May be on the other side of the car though.
https://youtu.be/hc1DRFqxPp0
No need to remove the bumper on the 335i. Hopefully similar on yours. May be on the other side of the car though.
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