10 replies to this topic

[james.o.potter@gmail.com]

Hi All!  I hope to your expertise can help...

 

After sitting through a very cold New York City winter (while I was laid up for two months due to a neurosurgery), my Mini started up okay, but is consistently pumping out white exhaust smoke.

 

I suspect the heated intake manifold water jacket is leaking internally, as it seems to be "steam-cleaning" the spark plugs (the 1 & 2 plugs appear more white rather than the regular tan).  Another thing to note is a small amount of initial white smoke behind the rocker cover in the engine bay upon startup which I think is leaking down past the carb spacer/manifold gasket - that whole area simply looks "wet" - see photos below.

 

Diagnostic Results:

 

• Antifreeze: Squeeze Bulb / floating needle tester says protected to -45°F; Voltage testing shows it is not overly corrosive (139mV w/no battery; 152mV when battery connected).  No leaks at all, and core plugs are intact, so although it got down to 3 degrees Fahrenheit while it sat outside, I don't think anything froze.

• Compression: Reasonably consistent (Cold: 165/170/170/158 Hot: 170/180/180/170 PSI). Cylinder #4's cold 158 PSI showed a jump to 197 PSI with a tablespoon of oil suggesting ring wear, not a cracked block or head gasket failure.

• Block/Gasket: No "mayonnaise" in the oil; no bubbles in the radiator; and a "no-inflation rubber glove test" on the radiator neck seem to show no signs of combustion gases entering the coolant.

• Exhaust: I get a "soaking wet" mirror test at the tailpipe (not slimy, so oil in the exhaust). And it's wet white smoke even after warming up long enough for the thermostat to open and the top hose to get warm (which should be long enough to dry out any condensation in the exhaust/silencer, I would think).

 

Questions: Do these heated manifolds often leak internally?  Should I perform a bypass test with a copper pipe to confirm, or is this evidence enough to save that time & effort and proceed immediately with a manifold replacement instead?  Or is the bypass test worth it in case there is some other cause?

 

Thank you in advance for any advice or guidance you can render!

Jim

 

Photos:

 Wet-Carb-Spacer-Brake-Servo-Side.jpg   172.15K   1 downloads

 Wet-Carb-Spacer-Rad-Side.jpg   166.44K   0 downloads

 Carb-Spacer-from-above.jpg   194.31K   0 downloads

 Warm-air-chamber-looks-damp.jpg   164.21K   0 downloads

 Corrosion-at-hose-connection.jpg   177.63K   0 downloads

[mab01uk]

Not seen a heated manifold leak internally myself but I guess it could happen due to corrosion over time or if there were any faults or weaknesses in the original casting which is now about 35 years old. Dissimilar metal corrosion could be happening where the pipe enters the alloy inlet casting.

 

It would be quicker and easier to do a bypass test with a copper pipe as you have suggested just to confirm if there is actually a leak, than to replace the inlet manifold, so I would do the test first.

 

In some climates you can run ok with the heated manifold bypassed but it may not be advisable in your region, especially in the winter months!

Edited by mab01uk, 14 March 2026 - 09:01 AM.

[james.o.potter@gmail.com]

Thank you for the super quick reply mab01uk! 

 

I agree with you, I'm going to get some 1/2" copper pipe and bypass the intake's tube and hope the white smoke doesn't continue. 

 

I will also grab some coolant bypass caps and seal the ends of the pipes on either side of the intake manifold just in case there is a leak open into the manifold throat (that way it won't be sucking in air instead of coolant and properly sealed, the air/fuel mix will be unaffected).

 

Any other thoughts anyone?

[panky]

White smoke can also be caused by a leaking brake servo diaphragm where fluid is being sucked into the manifold along the vacuum line. Usually though only happens when braking but might be worth checking the reservoir level and vac line for signs of fluid.

Edited by panky, 14 March 2026 - 03:34 PM.

[timmy850]

If it's a factory 90's manifold it could be a 5/8" bore rather than 1/2", so check that before you get the bypass tube

[bpirie1000]

I would suggest that the initial smoke may be condensation. As you say it was down tom3 degrees..

White plugs would suggest that your engine is running too hot or with a "lean" fuel mixture (too much air, not enough fuel).

Gas analyser at an mot centre may give you a fauge for where you sit. Does it rev freely or hesitant?

[james.o.potter@gmail.com]

First a couple of "Thanks!" and some feedback to the latest suggestions, then the results of the bypass test:

 

Panky: I recall reading something about brake fluid being a possible white smoke cause - I've checked my master cylinder level and there doesn't seem to be any loss.  Three of the servo vacuum hoses are the 30 year old factory heat-shunk vinyl so I can't simply pull them off to check for brake fluid, but I just found some 5/16" fuel hose with which I could replace the final segment that runs from the T junction and plugs into the banjo connection under the air cleaner box, so I will definitely check there.  Here's a photo of my servo hoses: 

 

 Servo-hoses_copy.jpg   81.63K   0 downloads

 

timmy850: I really appreciate the expert detail on the factory heated inlet manifold.  I already had a piece of 1/2" copper pipe, but your tip helped me get the right sized rubber caps to close off the inlet's two pipe ends, so thank you!.

 

bpirie1000: I thought it might be condensation but I ran the Mini until it was completely warmed up and it was still white, cloudy smoke.  And only plugs 1 & 2 were white, while 3 & 4 were closer to "normal", as if the coolant was only going into one side of the intake.  See photos below - plug 1 and plug 2 are in separate photos, while 3 & 4 are together in one picture.  I'm in the United States so I don't have a MOT center nearby   But it revs freely - if you can get to this link, this is what it looked like when blowing the white cloudy exhaust: https://photos.app.g...1Xw1DTRj3jQswz6

 

Plugs 3 & 4:

 plugs-3-and-4.jpg   29.11K   0 downloads

 

Plugs 1 & 2:

 plug-1.jpg   47.27K   0 downloads  plug-2.jpg   49.44K   1 downloads

 

Okay, on to the results of my bypass test:  I bypassed the coolant pipe in the inlet manifold with a copper pipe and the exhaust cleaned up quite a bit (see here: https://photos.app.g...4JA9gzoh9ttKhd7).
 

 Bypass-pipe.jpg   80.74K   1 downloads

 

All that said, others outside this chat have advised me that the heated inlet never leaks, but I think this is pretty conclusive, no?

 

But what with shipping and the tariffs, buying a new inlet (if it is not the root of the problem) is an expense I would like to avoid. 

If it seems to everyone here that the inlet is the cause, then it would be worth it to get a new one.

 

That said, I think there's another test I can try:

 

If I remove the carb and then disconnect the heater takeoff hose and then reconnect it to one side of the inlet (leaving the other side plugged) and then use a funnel & water in the hose to see if anything dribbles into the inlet throat...

 

Thoughts Folks?

[Ethel]

The steel hose connections are pressed in to the alloy casting. They couldn't leak internally, unless you managed to crack the casting. I guess that's possible, if it froze, but I'd expect it to leak a lot if it did.  If it was leaking externally, the steel pipes do rust & hoses can split, the air filter intake is in the right place to hoover it up.

 

Up to you if you think it's worth the effort, but you could rig up a sort of leak down test on the manifold with some plugged short lengths of hose & a tyre valve. I've also managed to work the steel ends out (Turbo manifold) & replace them with alloy tube, in order to reroute the plumbing.

[lsto]

Spray a little brake cleaner into the heater pipe on the manifold while the engine is running. If the revs change then it's leaking somewhere, if it's not then you should get no change.
That said if the car is running fine and not losing any coolant I would just drive it and not worry. If it's been sat a while or even some cheap fuel can contain a lot of moisture which shows as steam. Wait till you loose coolant or it runs rough before you worry.

Edited by lsto, 21 March 2026 - 01:55 PM.

[timmy850]

If you’re based in USA, you can try the suppliers below:

Wild Child
https://www.wildchildclassiccars.com/

Boot to Bonnet
https://boot2bonnet.com/

Heritage Garage
www.heritagegarage.com/

There’s also Jet Motors
https://www.jetmotorsmini.com/

Edited by timmy850, 22 March 2026 - 04:40 AM.

[james.o.potter@gmail.com]

That's brilliant Isto!

I was considering plugging the hoses back into the inlet manifold, and if the white smoke returned intensified, that would be my bellwether, but I was loathe to subject the cylinder internals to more wetness.

Not only do I have a can of brake cleaner, but I think I've actually got a spray can of Starter Fluid which should definitely kick the engine up if it is some how making its way through the manifold (with the bonus that I do not need to disturb my bypass to perform the test).

Such a good idea Isto - thank you!

And thank you as well Timmy850 - while I was aware of Jet, these other suppliers are new to me, so if I need to get the inlet and can do so from a shop on this side of "the pond", that would be great

I should be able to get out to my Son's place mid-week in order to report back (maybe my experiences here can save someone else some time and effort).

Thank you again you two!