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1961 390 Water in Oil

Started by whiskeyeagle, February 20, 2020, 09:37:56 PM

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Hello, I have 1961 Fleetwood with a 390 engine. We are experiencing water in the oil, milky dipstick. Ran a compression test and leakdown on the heads, and the compression test avg 140lbs, and the leakdown held 95lbs. Any thoughts where to go next to try to find the source of the problem.....Thanks Tim!
Tim Martin

79 Eldorado

Hello Tim and welcome to the forum. I'm not an expert on exactly what you are working on but a couple of things came to mind:
1) Some leaks will be more prone to leaking in one direction so you may need to check for leaks with the coolant side pressurized.
2) How long was it sitting? Could the water have been from condensation?


Mike Josephic CLC #3877

If you're seeing "mayonnaise" on the dip stick, I
would suspect a head gasket issue.  That is the
result of an oil / water mix due to a gasket leak.

To be sure, you'll need to have somebody check
the radiator inlet (under the cap) with a combustion
gas tester to see if you have exhaust gasses in the
coolant.  You may also be able to see bubbles in
the radiator fluid with the cap off and engine at idle.


1955 Cadillac Eldorado
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If you have a head gasket leaking combustion gases, if it's very bad, you will see it push your coolant out of the radiator too. But on a 390 engine about the only place that water can enter the oil is through the head gasket, if it is in fact a gasket.
You may have a crack in the block or possibly one of the heads, and when hot with a pressurized cooling system,  you will get a "bleed" of coolant into the inside of the crankcase once the engine is shut off. While it runs, the combustion pressure can keep the coolant from entering the crankcase. It just depends on where the crack is located.
I had an engine before that had a cracked cylinder wall, and the only time it would leak was after it was hot enough for the coolant to become pressurized, and then only after I had stopped the engine.
  The only way I found it was after I tore it down to inspect it. Never did figure out what had caused it to crack in the first place.
But one of two possibilities comes to mind.  The first is that it had frozen and the coolant was not strong enough to protect it.
The second was that it had overheated at some point in time.
You can test the cooling system with a pressure tester to see if it will hold pressure.  If the system is solid, it won't leak down. If it does, you may not actually be able to see where it leaks, because it would be an internal problem,  but at least you'll know you need to inspect it further.
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Mike, Scott & Cadman, thank you for the feedback.......

It is more than normal condensation. Our compression & leak-down test results seem to prove the head & head gasket are good. Now, the compression and leak-down test were performed on a cold engine, maybe that makes a difference.

I'm working on a setup to perform a pressurized test on the coolant system, I'm thinking that I will isolate the radiator from the test. Basically, block off the water pump output, and pressurize the coolant system at the water intake. I will post the results later this weekend....Thanks again.
Tim Martin

James Landi

Please note Scott's word of caution.  I owned a 61 decades ago, and during the winter months, I experienced a good deal of condensation in the oil, so that withdrawing the dip stick gave me the impression that a good deal of water was trapped in the oil. Your engine has no pvc, and combustion blow-by is designed to exit via a pipe from the valve valley that finds its way under the car.  As a consequence, most of the water that occurs during cold weather start ups and short runs winds up trapped in the engine oil, especially on the rocker arms, and in the dip stick tube, where additional condensation forms. Believe me, during cold weather, it rains in there, and only lengthy runs "cooks" off the condensation. Here are some questions before you begin to do surgery:  Are you frequently starting and stopping your engine this winter?  Do you take your car for only short runs.   Is the milky mixture only on the top of your dip stick or, if you were to drain the oil entirely, would ALL of the fluid be a mix of oil and water. Is there a good deal of smoke coming from the oil fill when you remove it.  Are there water droplets on the inside of the fill? If you stick you finger in the oil fill do you find white gunk? My 61 had a good deal of blowby and a bunch of white gunk in the winter months.  You can create a DIY PVC for the engine-- it's simple. James


I guess you mean coolant in oil?
If stored with water in it, you got a bigger problem.
First thing to do is drain well and change the oil and see if it persists and not a one time occurrence.   If worried about costs, use used/cheap oil since temporary.   
Since compression is good, there's a bunch of other places where coolant can get to the oil side, either by crack or gasket fail.   '61 was re-designed so they took care of some of the past issues.

James Landi

One other point before you take things apart.  If you  think you have a leaking head gasket on the compression side of things, youll  see a stream of bubbles if you run the engine with the radiator cap off.   The compressed gasses have to escape!  Hope this helps.   James