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'51 Desoto blowing white smoke when accelerating


Tim Larson

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Trying to figure out why a '51 Desoto would be blowing white smoke. It seems to only happen when accelerating - especially from a stop or very close to a stopped position.

 

The coolant level is good and normal even after driving 250+ miles. The oil was down below add and I had to add two quarts to bring it above the add mark.

 

I was told it had a ring job done and the pan was dropped and cleaned. 

 

The car has really seen very few miles. Is it possible that the rings are seated properly yet? I don't know when this job was done exactly.

 

Would adding seafoam or marvel mystery oil to the crankcase do anything? 

 

Right now it is running 10w30 oil, but maybe that is too lightweight. 

 

Otherwise the car runs and drives well with very little hesitation. 

 

Appreciate the input. 

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sure sounds like it is burning oil, and under acceleration it could be a ring issue.

I once had a engine rebuilt, and it smoked when I got the car back on Friday. I drove it and put about 2 quarts of oil in it and it was still smoking.

On the Monday after Jan 1st. I brought it back. It turns out they installed the rings upside down.

Was the Friday before Christmas and they worked late to finish all jobs to take the week off after Christmas.

 

They had no issue taking the engine back out when I told them I had already put 2 quarts of oil in it, they expected some oil loss while rings seating, but 2 quarts was just wrong.

 

I hear some rings, maybe chrome molly? they take longer to seat ... Seems like a compression check is in order. 

Rings can stick to the pistons after years of sitting, then they wont expand properly to seal. The rings need to move freely in the groove.

If they are frozen, it might do exactly what you are describing.

 

A compression check may tell you that 5 cylinders are working correct, and 1 cylinder has very low compression. In this case, you may be able to fill that cylinder with some marvel mystery oil or something else, and get the rings to free up.

Same time, if all the cylinders are low on compression, I would suspect a bigger issue and a tear down to find it.

 

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Yes. Perform a dry and wet compression test. Post both sets of  numbers. Ensure battery is fully charged and strong. Remove all spark plugs. Mash throttle wide open then crank engine over. 

 

That outta tell ya some clues about whats causing smoke. 

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Burning oil would cause blue smoke. White smoke is typically coolant being burned. 

 

Coolant leaking into to cylinders could be be a warped or cracked head, bad head gasket, cracked block and so on.

 

Maybe start by checking the oil for signs of coolant such as a milky appearance. Also try re-tourqing the head to spec and see if that helps at all. A compression test as mentioned above will also be a helpful diagnostic.

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If your spark plugs are white then check the fuel mixture in the carb.

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2 hours ago, keithb7 said:

Yes. Perform a dry and wet compression test. Post both sets of  numbers. Ensure battery is fully charged and strong. Remove all spark plugs. Mash throttle wide open then crank engine over. 

 

That outta tell ya some clues about whats causing smoke. 


I will give this a try. What is the ideal number(s) that I am looking for?

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Here at my elevation 90-100 psi is ok. 100+ is decent. Dry. 

 

Lower than 90, the engine is getting tired. More than a 10% difference between cylinders also generally means repairs should be considered. 

 

If you add oil to your cylinder and your psi goes up at the next test,  the rings are worn. In my opinion if you have 90 dry, add oil, and hit 100 that’s reasonable for a old engine. Not necessarily due for an overhaul in my opinion. Over the past 2 1/2 years I’ve put 5,000 miles on my 265 engine with 90 dry, 100 wet compression test numbers. 

 

If you have a low number, for example 75 psi, you add oil and the reading does not go up, you likely have valve sealing issues. A valve grind, or replacing a burnt valve will likely get the psi back up. Unless you have both worn valve surfaces, and worn piston rings. 

 

Look at your plugs when you pull them. Look for signs of burning coolant deposits. A bad head gasket or a cracked head/block could allow this.  Also look for black soot from burning oil on the plugs.  My #1 plug is always a little darker as #1 has a worn valve guide. It sucks oil into the cylinder when going down hills, when using engine braking. 

 

Be warned! Before removing the spark plugs, blow compressed air around the spark plug base in the cylinder head. These areas are prone to hold dirt, lost tiny screws, or anything else. Its just waiting to fall into your combustion chamber as soon as you lift the plug out. I learned the hard way here. 

 

 

Edited by keithb7
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2 hours ago, tjlarson88 said:

Thanks for the suggestions. Here is the appearance of the oil before I added last night. I don’t think it looks milky, but I certainly could be wrong.

 

 

8D97DC74-A375-46C9-810A-DE8478F156B1.jpeg

That oil looks normal to me, no coolant mixed in. Was the car running okay and then suddenly began to put out the white smoke? Good luck to you.

John R

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1 hour ago, John Reddie said:

That oil looks normal to me, no coolant mixed in. Was the car running okay and then suddenly began to put out the white smoke? Good luck to you.

John R


Yes, the car has always run fine. It seemed to only blow white smoke when accelerating after rounding a corner or similar driving that would call for acceleration. 

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1 hour ago, keithb7 said:

Here at my elevation 90-100 psi is ok. 100+ is decent. Dry. 

 

Lower than 90, the engine is getting tired. More than a 10% difference between cylinders also generally means repairs should be considered. 

 

If you add oil to your cylinder and your psi goes up at the next test,  the rings are worn. In my opinion if you have 90 dry, add oil, and hit 100 that’s reasonable for a old engine. Not necessarily due for an overhaul in my opinion. Over the past 2 1/2 years I’ve put 5,000 miles on my 265 engine with 90 dry, 100 wet compression test numbers. 

 

If you have a low number, for example 75 psi, you add oil and the reading does not go up, you likely have valve sealing issues. A valve grind, or replacing a burnt valve will likely get the psi back up. Unless you have both worn valve surfaces, and worn piston rings. 

 

Look at your plugs when you pull them. Look for signs of burning coolant deposits. A bad head gasket or a cracked head/block could allow this.  Also look for black soot from burning oil on the plugs.  My #1 plug is always a little darker as #1 has a worn valve guide. It sucks oil into the cylinder when going down hills, when using engine braking. 

 

Be warned! Before removing the spark plugs, blow compressed air around the spark plug base in the cylinder head. These areas are prone to hold dirt, lost tiny screws, or anything else. Its just waiting to fall into your combustion chamber as soon as you lift the plug out. I learned the hard way here. 

 

 


Keith, I appreciate the information and always value your input. 

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The oil on the dipstick tube does look good to the naked eye..

White smoke..Blue smoke...Depending on how bad/thick it is, it all kinda just looks like smoke to the average person. Experienced folks can see and smell the difference between burning coolant, burning oil, or black smoke from a rich A/F mixture.

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There is also the disappearing oil which seems excessive and coolant is uncontaminated and constant level. If you don't have terrible leaks you are buring the oil.

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12 minutes ago, 1949 Wraith said:

There is also the disappearing oil which seems excessive and coolant is uncontaminated and constant level. If you don't have terrible leaks you are buring the oil.

 

The car does seem to drop a patch of oil every time it is shut off and parked - in a driveway/on the street, etc. I noticed this driving it home when I would look under it at the gas station. I made sure to check the oil and it did not ever seem low to me. My question is where it is coming from. The puddle doesn't seem to form under the drain plug on the oil pan - it seems to be under where I think the fluid drive is between the transmission and the engine. Would there be a way to tell if this oil is engine oil or fluid from the fluid drive? Since this car doesn't have the fluid torque drive it shouldn't share the engine oil with the fluid drive, correct? 

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Take a close look at the timing chain cover at the front of the engine. If the seal is leaking oil will blow back and collect on the rear of the engine. The other likely source is the rear crank seal. No need to ask why my P15 and I know about these leaks......

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6 minutes ago, Sam Buchanan said:

Take a close look at the timing chain cover at the front of the engine. If the seal is leaking oil will blow back and collect on the rear of the engine. The other likely source is the rear crank seal. No need to ask why my P15 and I know about these leaks......

 

After all the reading I've done on this forum since June I definitely had the rear main seal come to mind....

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Some knowledgeable guys looked at the Desoto this morning and were amazed at how well it ran, sounded, and looked. They did notice some possible oil leakage around the filter canister so that is a possibility - the seal under the cap might need to be changed. Nothing major or super worrisome so that is good to hear and what I figured. An almost 300 mile trip for a car that has seen extremely limited use in the last MANY years is quite a stress on it. 

 

This is all part of the experience in own a car of this era. They will never be completely perfect since they never were in the first place. Keeping an eye/ear on the car's operation is essential. 

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