Oil in Coolant - 1994 5.0 - Vintage Mustang Forums
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post #1 of 7 (permalink) Old 09-13-2018, 02:23 PM Thread Starter
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Oil in Coolant - 1994 5.0

Not really a Fox....but close!

I posted this at Corral.net and got nothing, so I figured some engine Gurus around here might have some insight.

I bought a 1994 GT with a T5 that has oil getting in the coolant. I knew this up front, basically stole the car for he wanted. The car was a good friend's, he had it diagnosed as a cracked block from a shop I do not know about. I got it from Texas to Wisconsin with me and before I started ripping into it, I decided to verify the block claims.

Here is what has transpired:
-- There is DEFINITELY oil in the coolant, but not enough to turn it into sludge, just make a thick oil slick on top
-- There is NO (repeat:NO) coolant in the oil. I drained it the other night with no signs of water in the crankcase at all. The oil change is not "fresh"
-- I put a pressure tester on the radiator, cranked it to 19 psi, and let her sit. No drips in the 30 or so minutes I was watching the oil pan, also no external leaks. I left the tester on the car and called it night. The next morning I pumped it back up once to 19 after it lost about 2psi over 12ish hrs. I have now had the pressure tester on for 36 hours now with no real pressure loss (maybe another 2 psi). The plan is to pull the drain plug again and see if water made its way into the crank case.

So It's an interesting conundrum that oil is only passing one way. There's not a whole lot of areas where those two fluids interact that would cause this.

I'm starting to wonder if a jiffy-lube tech put oil in the coolant overflow and sent the car down the road...

Any thoughts would be appreciated! I will probably do a compression test and inspect the plugs next. I fall seems good there, I will probably flush the coolant system really well with some dawn and see if the problem comes back.

TIA!

eventually a 1969 Mustang Fastback--been in hibernation since 2011 due to school...
Now the time has come to resurrect her once and for all!
Currently on a body cart with a finished undercarriage.

Last edited by GypsyR; 10-03-2018 at 10:44 AM. Reason: clarification
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post #2 of 7 (permalink) Old 09-26-2018, 01:50 PM
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In sentence #3 you said "coolant getting in the oil." You need me to fix that?

I'm tending towards a cracked block too. You might want to consider that this theoretical crack may not open until the engine is fully up to operating temperature. Pressure is a factor too. Oil pressure when cold can be up around 50 psi, the cooling system will never be close to that. So the higher pressure fluid will always win.

On the bright side, I personally would think nothing of tossing a used 5.0 in it and motoring on. You want a roller cam "HO" engine though. You can find non-roller 5.0's really dirt cheap but your EFI will be unhappy. (Not work) You can make it work by swapping in a 351W flat tappet cam and lifters. Or putting in some kind of roller cam retrofit cam kit. Both options kind of negate the dirt cheap factor though. And no, you can NOT simply swap the plug and injector wires around to fool the computer into thinking you have the HO cam in it. Been there, done that. Focus on a cheap roller cam 5.0, an Explorer or something if you want simple and cheap.
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post #3 of 7 (permalink) Old 10-03-2018, 01:38 AM
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"There is DEFINITELY oil in the coolant, but not enough to turn it into sludge, just make a thick oil slick on top."
Define "thick oil slick". When you put your finger in it, do drops of oil stick to your finger .... or does it just poke through a rainbow coloured film?
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post #4 of 7 (permalink) Old 10-03-2018, 02:14 AM
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Does it still have the oil cooler on it? If so I'd look in that direction. What do the plugs look like? Not to mention if its an auto I have seen the internal trans coolers rupture leaking trans fluid into the radiator.

Scott

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post #5 of 7 (permalink) Old 10-03-2018, 09:17 AM
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OP states it has a T-5
Being a Texas car I doubt a cracked block from coolant freezing ,possibly from severe over heating but you would notice other issues. I could see maybe a bad head gasket ?
Explorer 5.0 FTW


Brad
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post #6 of 7 (permalink) Old 10-03-2018, 09:27 AM Thread Starter
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My apologies on the sentence #3...there is OIL in the COOLANT only - please do fix for my Gypsy.

T5 so not worried about ATF in it.

The oil slick I would estimate at 1-2 mm thick on top of the rad. Not just a "sheen" of rainbow oil color.

No oil cooler I am aware of, all my reading shows that started on the 4.6L.

I'm going ot flush the cookies out of it and put some miles on the car. The original owner was a oil change deal of the week guy, so I'm not past the thought that Johnny McJiffyLube put oil in the coolant overflow.

I'll keep you all updated, I got busy then was out of town for a while. I fit does need an engine, there are several 5.0 roller block donors withing 20 miles for $400-$600 out there. Might drop a set of Chinese aluminum heads and port the intake really well if I go that route

eventually a 1969 Mustang Fastback--been in hibernation since 2011 due to school...
Now the time has come to resurrect her once and for all!
Currently on a body cart with a finished undercarriage.

Last edited by 69StangRestomod; 10-03-2018 at 09:29 AM.
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post #7 of 7 (permalink) Old 10-08-2018, 09:23 PM
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That fact that you pressure tested it over night and only went down a little bit could be related to the connections. Oil getting into the coolant. My thoughts are the oil is a low pressure area outside of the galleys. The coolant is high pressure. Something in a low pressure area is not going to migrate to a high pressure area. Coolant in a high pressure area will however migrate to a lower pressure area such as the crank case. Since there is no oil in the crank case like you said kind of confirms that.

I would flush the radiator a few times and see what happens. I would use plain old water if it's not freezing, I don't think you need to worry about that right now. You have a 24 year old car, who knows what a PO has done?

Even if it is a crack in the block I'd slam in a Exploder short block
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Tom

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