1998 Ford Mustang Gt, Oil(mixed with coolant) flowing out of the coolant resivior.

Calhuff

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Jan 24, 2019
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1998 Ford Mustang GT (startup after 9 years) The engine started right up, and as I watched the engine after it had started, Light brown oil (obviously mixed with coolant) started to flow very quickly out of my resivoir. Also, I found that the oil and coolant mix was found everywhere in the cooling system including the thermostat, but it was not in the oil pan when i drained it. after doing research, most people said it was the head gasket. I found that difficult to believe because of how fast the oil was spewing out of my coolant resivoir. further research told me it could be the oil cooler gasket... I took the oil cooler out (water and oil mixed were inside the oil cooler) but the adapter gasket was in perfect condition. No faults or anything. I decided to test my oil cooler by sealing one side off to a block of wood, and putting the water in where the coolant would usually go. I did this and water began to flow out of the oil cooler where the oil filter would be if it was connected. Is that suppose to happen? Is it possible for there to be a fault or internat crack inside the oil cooler allowing them to mix? are there aftermarket solutions or do i pay $400 for a brand new oil cooler?
 
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Azazel6221

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Jan 24, 2019
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1998 Ford Mustang GT (startup after 9 years) The engine started right up, and as I watched the engine after it had started, Light brown oil (obviously mixed with coolant) started to flow very quickly out of my resivoir. Also, I found that the oil and coolant mix was found everywhere in the cooling system including the thermostat, but it was not in the oil pan when i drained it. after doing research, most people said it was the head gasket. I found that difficult to believe because of how fast the oil was spewing out of my coolant resivoir. further research told me it could be the oil cooler gasket... I took the oil cooler out (water and oil mixed were inside the oil cooler) but the adapter gasket was in perfect condition. No faults or anything. I decided to test my oil cooler by sealing one side off to a block of wood, and putting the water in where the coolant would usually go. I did this and water began to flow out of the oil cooler where the oil filter would be if it was connected. Is that suppose to happen? Is it possible for there to be a fault or internat crack inside the oil cooler allowing them to mix? are there aftermarket solutions or do i pay $400 for a brand new oil cooler?


I just had this problem with a different vehicle your oil cooler went get a new one its pumping the oil into the coolant system thats why its not in the motor
 
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2006FlatBlack

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Dec 3, 2019
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I'm having same problem with a 1998 3.8 manual transmission. The $400 oil cooler mentioned, is it motor oil cooler? Where is that located?

Thanks.
 

tsemmett

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I'm not sure a 98 3.8 has an oil cooler (I had a 91 3.8 that did not). Head gaskets are a common point of failure with the 3.8 though; I'd be testing for that (leakdown for instance).
 

2006FlatBlack

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I checked yesterday and there is no oil cooler. I did compression test and all 6 came in between 150-160. I also did a pressure test on cooling system and it does not lose pressure. I read on another search that it could be the timing chain cover?
 

tsemmett

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Timing cover could make sense; the water pump passages go through it, like a small block. Intake manifold could also make sense (coolant flows through it, and a leak could drop coolant in the valley to drain down into the oil pan). I would think if either of these were leaking, you would lose pressure on a pressure test though.
 

Pepe 98v6

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Mar 29, 2020
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Timing cover could make sense; the water pump passages go through it, like a small block. Intake manifold could also make sense (coolant flows through it, and a leak could drop coolant in the valley to drain down into the oil pan). I would think if either of these were leaking, you would lose pressure on a pressure test though.

It can’t be either because we’re talking about oil in the coolant tank but no coolant in the oil. Anybody have anything else I can check?
 

STEVE PATTON

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Jan 6, 2019
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1998 Ford Mustang GT (startup after 9 years) The engine started right up, and as I watched the engine after it had started, Light brown oil (obviously mixed with coolant) started to flow very quickly out of my resivoir. Also, I found that the oil and coolant mix was found everywhere in the cooling system including the thermostat, but it was not in the oil pan when i drained it. after doing research, most people said it was the head gasket. I found that difficult to believe because of how fast the oil was spewing out of my coolant resivoir. further research told me it could be the oil cooler gasket... I took the oil cooler out (water and oil mixed were inside the oil cooler) but the adapter gasket was in perfect condition. No faults or anything. I decided to test my oil cooler by sealing one side off to a block of wood, and putting the water in where the coolant would usually go. I did this and water began to flow out of the oil cooler where the oil filter would be if it was connected. Is that suppose to happen? Is it possible for there to be a fault or internat crack inside the oil cooler allowing them to mix? are there aftermarket solutions or do i pay $400 for a brand new oil cooler?
I have a 98 gt that had the same problem, it was intermixing in the aluminum oil filter/cooler adapter. The casting was very porous.
 

wmburns

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Aug 14, 2009
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It can’t be either because we’re talking about oil in the coolant tank but no coolant in the oil. Anybody have anything else I can check?
I don't think you understand what we are trying to tell you. At the oil filter adapter on the side if the block there is a spot where the output of the oil pump and the lower radiator hose comes together. There is a gasket there that keeps the oil and coolant separate.

Think about it. Because this spot is before the oil filter this is where oil pressure is at it's maximum. So if the gasket as failed this would offer a "possible" point where the oil pressure would force the oil into the coolant but not the other way.

Does your car have an automatic trans?
^^^This is also a insightful possibility. At first glance how could one tell the difference between motor oil and transmission fluid? Is this motor burning oil? What about the transmission fluid level? This may be something straight forward as a rotted out radiator.
 
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Pepe 98v6

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I don't think you understand what we are trying to tell you. At the oil filter adapter on the side if the block there is a spot where the output of the oil pump and the lower radiator hose comes together. There is a gasket there that keeps the oil and coolant separate.

Think about it. Because this spot is before the oil filter this is where oil pressure is at it's maximum. So if the gasket as failed this would offer a "possible" point where the oil pressure would force the oil into the coolant but not the other way.


^^^This is also a insightful possibility. At first glance how could one tell the difference between motor oil and transmission fluid? Is this motor burning oil? What about the transmission fluid level? This may be something straight forward as a rotted out radiator.

When I said it couldn’t be either I meant the timing chain cover or intake manifold because they were stating coolant leaking down into the oil pan

I pulled the oil filter and the oil pump found an o ring(in good condition) but no *gasket*

I have a 98 base model mustang(v6 not a v8), so I don’t have an oil cooler in between the filter and the pump it looks like it just becomes the engine block after the oil pump it doesn’t look like coolant passes through/around the pump so I don’t understand why even if that o-ring was bad or if their was a gasket missing why it would be leaking into the coolant and not just straight out
 

o willingham

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May 14, 2020
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Pepe,

I had the same problem with my truck. I don’t know if it’s the same, but I had transmission fluid mixing with coolant. It looked like coffee. I found out the transmission fluid rans through the lower part of the radiator to help cool it. The radiator failed, which allowed the coolant, and transmission fluid to mix.