BMW 628csi rough running

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Boltneck
Posts: 1
Joined: Wed Sep 01, 2021 7:51 pm
Location: UK

BMW 628csi rough running

Post by Boltneck »

Hello all,

I have a UK spec 1986 628csi automatic and it has started to run rough on cold starting.

It appears to be running on 4 or 5 cylinder for about 20 seconds and then clears and runs normal.

I can go for a drive for 30 minutes, then turn the engine off for 30 minutes, and when I start it it behaves the same (rough running for 20seconds or so).

If I release the pressure from the header tank after I switch off, it runs fine when I go back to start it.

I've also noted that the temperature does not show normal on the gauge and only gets to about 25% (50% being normal).

Also, the cooling system doesn't seem to pressurize as much as it used to do.

I am losing a little water but not a huge amount (I have to top up the header tank after 100 miles or so). There are no external leaks.

So, my question is, where is the coolant going? Could the radiator have failed between the coolant and the integral oil cooler for the transmission?

Or have I got a head gasket failure?

Engine oil is clean, coolant is clean, auto transmission oil level is steady, and no white smoke on startup.

I've had the car since 1989 and it's now done just over 100,000 miles and never been abused so would be surprised if the head gasket has failed.

Are there any other checks I can do before taking the head off?

Thanks in advance.
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86_6series
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Joined: Mon Apr 02, 2007 10:08 pm
Location: West Nyack, NY

Re: BMW 628csi rough running

Post by 86_6series »

Do a leak down test to insure you have a head gasket problem.

Pressure test cooling system to see if leaking.

Run engine with pressure tester on cooling system to see if pressure builds.
86-635CSi
96-MB C220 SOLD
98-740i
71-Continental MK3
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