Need a diagnosis - white smoke! UPDATED

1971 MGB GT

Been driving the car almost daily. Today went out to run some errands and noticed white smoke coming out of the exhaust. It seems worse when I decelerate and between shifts it really puffs out. Small amount of smoke when idling.

oil pressure is good
used a laser temp gauge and the top hose is 20-30 degrees hotter than the bottom hose
coolant level OK
no visible leaks around the head
no yogurt on the inside of the oil filler cap
no fuel additives

I'm worried................any suggestions as to how to track down the problem or what it may be?

Sounds like water. Might be your head gasket is leaking internally and no visible external leaks are detected. OR and hopefully not, you have a crack in the head. JMHO. PJ

Is this just when the engine is cold or does it happen when fully warmed up too.

White smoke is normally a sign of coolant burning.

Happens fully warmed up. Just pulled all the plugs and they're dry and normal.

No tell-tale moisture on head.

Are you sure the smoke it white, and not blueish white? puffing between shifts is usually oil smoke from worn rings, and someone who"s not experienced in mechanics could easily mistakeingly describe oil smoke as white. Are you seeing any loss of oil,(other than normal loss from leaking, ha,ha), or any noticable loss in coolant?
Just a thought.

Time to do a coolant system pressure test and a leakdown test. At the very least they'll put your mind at ease. Basil

No loss of oil. I changed it about 500 miles ago and haven't used a drop......except for a couple of drips in the driveway!

I'll take Basil's advice and have it checked out.

Funny thing is, it runs great at all speeds. Just had it up to 65mph on the highway. When my foot is on it, no visible smoke, when I let off the gas, I can see it.

Thanks all.

White smoke means water. The only places water can come from is carb or coolant. Need a lot of humidity coming into carb to make a lot of smoke though. Blown head gasket, cracked head, warped head, or cracked cylander wall. Try draing the oil in a pan and look for yogard. Does should like the head needs to come off which wouldn't be a bad idea anyway just to make sure. Have a machine shop check it though as some cracks are hard to find. Just thinking you may have a snapped head stud.

Does your car have a servo? Been known to fail and pull brake fluid into the manifold. Your smoke seems to exist during high vacum periods, so it could be the case.

Pete

White smoke can be from excessive fuel as well (fuel vapor looks an awful lot like water vapor). How's your fuel mileage?

Seems to me that with the car hot and stationary someone could be running it at 2000 rpm anile you put your hand over the tail pipe. moisture on your hand would be noticeable. You'll normally get mopisture when the car is warming up so you could feel it then to see what it is like.

A coolant system pressure test at 15psi seems to me rather unlikely to disclose a leak that happens only when warm.. But is certainly a straightforward way to start even if lack of a leak then doesn't necessarily mean all that much. Of course the presence of a leak then does deserve attention...

Sure is smoke and not steam..? also know as (condensation). Usally this time of year you will see it more offten..

I had white smoke one time in another car - I changed the PVC valve and preseto it was corrected and teo years later still no white smoke. I don't know why or how it fixed it but it did. Maybe ?? Just an idea to explore???

Bluish white = Valve seals. The key here is when decelerating and when shifting. Sucks oil into the combustion chamber through the valve seals.

White = Head gasket. The key here is when decelerating and when shifting. Sucks coolant into the combustion chamber through the head gasket.

IMHO

Bob

OK, I just got back from Carriage Craft in Reading. (the 35 mile ride up was a hoot as I was billowing white smoke/steam).

Anyway, it's the head gasket. They did a compression test and they're all good at 155lbs. Looking into the spark plug holes, there was moisture on the piston in #4 cylinder. With the radiator cap off, they hooked up an air pressure fitting to #4 plug hole and when air was applied, the radiator bubbled. So, I'm having the gasket replaced with a Payen (sp?) set that they showed me as well as having the head checked for straightness and hardened valves installed for unleaded fuel.

Thanks for all the replies.

Don't forget to have it magnafluxed. More of these heads crack than blow head gaskets.