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Oil in Coolant: Pulling it all together

01-31-2012, 04:19 AM
I have read every single post that I could find about oil in the coolant. There are some excellent posts, but I find myself not quite decided upon my trouble shooting process.

First the basics: I have a 2000 Windstar, 3.8 l engine, towing package with 180K miles. Van runs fine, but does have some kind of intermittent thumping kind of miss at idle.

Problem: Oil in Coolant reservoir- just recently found reservoir low, but that has not typically been a problem.
Done so far: drained a little oil out of pan: saw no evidence of coolant in oil(I know that does not necessarily mean anything until tested)

So, I have gathered info from the various posts about potential causes:
Head gasket
Engine front "cover" or housing
Lower intake manifold
Oil cooler(for towing package)

My temptation is to pull the engine and perhaps re-build since I have high mileage, but I dont really want to do that. I know many of you have written a lot on the subject and I did not ignore, so if you can bear with me, I'd like to get to the bottom of some of my questions.

Head Gasket- that is a no brainer that it would cause this problem so I'll leave that aside. For what it is worth, I see no external leaks at heads.

Engine front Cover/housing: I'm not wanting to go there yet, but I can see where it could cause the problem.(I see no external leaks)

Lower Intake: This is where questions arise. It seems like an easy enough repair, but I cannot see how it would cause so much oil to get into the coolant? What am I missing there?

Oil Cooler: I have towing package, but I do not have an oil cooler that I can see(and I have looked hard) Ford does not list that part as far as I can find.

Radiator: Here I can only see the potential for transmission fluid. The oil in my coolant reservoir smells like engine oil, and it is black but still not 100% sure of what it is. I once had a Chrysler that had a cross between trans fluid and coolant. Does anyone know if this is physically possible with the design of the windstar radiator?. If so, what is best way to test? My trans fluid "looks" fine.

So I am trying to decide where to start: It seems as though if I do the lower intake gasket job, I might as well change head gaskets, because I cannot be sure the lower intake gaskets alone will resolve the problem. What is the best way to check if head gasket is the issue before tearing into it?

Thanks to all

northern piper
01-31-2012, 06:56 AM
well if it were me, I'd be getting a sample of that oil and sending to Blackstone Labs. They have an amazing ability to tell you likely where things are going wrong. It's kind of like running bloodwork on your van. I've used them multiple times with excellent results. I sounds like you've got a good handle on what it "could" be, and how to do the repair, but you could do all those repairs and still not hit the problem area. For the $30 it costs, send them a sample and see.

01-31-2012, 09:14 AM
I have the trailer towing package on my '99. I was never absolutely sure what changes there were but "I think" they include: (1) a more robust radiator. and (2) a heat exhanger mounted in front of the radiator ... that had one circuit for tranny fluid, and one circuit for powr strg fluid. I believe the additional engine oil coolers were only used on special service units such as police, military, taxi .... commercial fleet orders.

I agree with using Blackstone Labs .... I would send a specimen of the coolant. If anything .... I would be more apt to dive into a total rebuild because of the miles on your vehicle. Doing a total rebuild is like getting a new engine. I have rebuilt this engine .... for me, better to remove the manifolds and heads ... and then carry the engine to the workbench as a "short block". You will do a much better job once the engine in out in the open and you have wrench-space.

This is a leaky engine, and after 100k miles or so ... the gaskets and seals just start "letting go". (But not the head gaskets ... they are pretty robust). The lower intake and front cover are both "wet" ... that is, they have coolant thru them and have crankcase "exposure". Either can leak in either direction.

My rebuild has about 120k miles and 5 years on it .... and I can now detect early gasket/seal leakage. So even though it runs very well and has perfect compression ... I may open it up again this summer and replace all seals and gaskets again. Of course, the valves will be redressed, etc.

As far as the tranny leaking into the coolant. Its possible ... the radiator has the possibility of crossover .... but I have never heard of it on this car. Tranny fluid is at very low pressure .... so it would most likely be "coolant-into-tranny".

01-31-2012, 10:15 AM
Thanks for your replies. I get the idea of testing for coolant in oil. As for oil in coolant, I can clearly see and smell that it is oil.
On my question about the lower intake gasket: how do you see significant amounts of oil getting into the coolant via an intake gasket breach from cooling jacket to intake. It seems to me that the coolant pressure would always exceed the intake pressure. Clearly I can see how coolant gets into the oil as it would get sucked down the intake and into the cylinder which has been shown by another poster but not visa-versa. What am I missing here?


01-31-2012, 10:40 AM
OK, I perhaps now understand your question about the lower intake manifold and gasket. The front cover has both coolant passages and high pressure oil passages going through it ... coolant pump and oil pump mounted to it. But I don't remember exactly the lower intake .... does it only have coolant passages and not high pressure oil? I think that is the case.... no high pressure oil. As far as coolant pressure aways being higher than intake (crankcase?) pressure ... think of what happens at start up before the coolant is warm. Remember a coolant leak could be directly into the crankcase ... and not thru the intake system.

01-31-2012, 11:36 AM
I see what you are saying about coolant going directly into the crankcase. From the pictures, if the intake gasket would fail on the lower side, it would drip directly as you said. Of course I have not tested the oil, but see no signs of that. Furthermore, my real identified problem is oil in coolant.

The area just beneath the lower intake is not flooded and pressurized with oil to my knowledge, so I still have a hard time picturing oil splashing into a breached area of the coolant port on the in the intake gasket and making its way into the coolant. Again, I feel like I am missing something here because there has been a lot of discussion surrounding the "oil in coolant" problem being identified with the lower intake gasket. I'm thinking that I could replace the lower intake gasket(which, of course would be a good idea), but it not really solving the original problem.

Perhaps I need a really good way to test the head gasket to rule that out. What is the best way of doing that? Compression test? I did read someone posted about compressed air in the spark plug hole and looking for air bubbles or rising coolant as an indication of a breach from cylinder to coolant passage when there is not external leaks? Thoughts?

01-31-2012, 03:40 PM
Well, I believe you are correct in your skepticism of the lower intake gasket allowing oil to get into coolant .... possible, but not as probable as the front cover which has both fluids passing through. The head gasket would be last on my list ... just because I believe it is so robust. I list them this way, in likelihood of passing oil into the coolant:

(1) Front cover and gasket: Easy choice ... oil and coolant pass through.
(2) Lower intake manifold and gasket ... will pass oil into coolant as engine cools and coolant pressure goes negative...."sucking" pooled oil into coolant.
(3) head gasket. Certainly looks risky ... the oil passages and the coolant passages are so near. But I have never seen a properly installed head gasket even come close to failure .... but that don't mean it don't happen!!

That's my guessing....

01-31-2012, 03:45 PM
BTW, if the head gasket fails ... and I have seen it fail on this engine. (Always suspected poor installation.) .... if the head gasket fails, the coolant is likely to "boil", and it will be impossible to keep coolant in place. Or, at least, that is what I have seen.

01-31-2012, 07:45 PM
Oil cooler.
I did not have one...but the manual for my '96 shows it.
The oil cooler, if it is there is a small unit that fits onto the oil filter mount...and the oil filter screws into the cooler.
In other words.....it is a plate that is about 1" that is sandwiched between the oil filter and the place the rest of us put the oil filter onto.
The ONLY way that I would be able to know if I had the oil cooler on the engine is to look for the pipes on it....which coolant hoses connect to.
If you have coolant hoses going to pipes that seem to go into the base plate that the oil filter screws onto......then you have the factory engine oil cooler.
If you don't have the coolant lines there, you do not have the vactory engine oil cooler.

I am also thinking that you do not have a bad head gasket....
I would lean toward the front cover.....also known as timing cover.
Sadly, it is a lot of work to replace that gasket......cheap part....and the new ones are improved, so that they will not fail (if installed correctly) but it is a MAJOR repair.
I had the front cover gasket start to leak VERY slightly......coolant leaking out....a FORD dealership told me not to worry about it unless it got worse....that it was a $1200 repair.
At the time.....the repair process started with "remove engine from vehicle".
They have modified that now......but you still have a LOT of work.
What I did was put the original pelleted BAR's Stop Leak into the radiator.
That sealed it up for MANY MANY miles and years.
The Bar's did NOT solve a leaking lower intake manifold gasket (although it did slow it down....again.....it was a very slight leak also....but coolant into the oil).

01-31-2012, 08:10 PM
So, here is where I am with this.
Front cover and gasket- I agree. Easy choice as potential culprit, but hard to change and would like to rule out other things first.
Intake- At what point does the coolant go negative pressure?- decrease in pressure I can see, but negative with respect to crankcase or atmosphere? I know I wont let go of this, but I still am missing something that gives me a plausible explanation for how lower intake gasket can cause oil in coolant..

Head gasket (HG)-I know I have oil in coolant- seems that the guys with the chemical method for testing for hydrocarbons in coolant would say that's all they need to know to determine head gasket failure. You said in your last comment that your experience is that a HG fail will cause overheating. I have seen this as well. Perhaps, I am just seeing the early stage of the HG fail (i.e. some "blow-by" of exhaust into coolant, but not to the point where it is causing massive gas pockets and any over pressurization of coolant system is just being bled of by cap)
After reading around a bit, I believe I want to pressurize each cylinder at TDC and look for bubbles or rise in coolant level.

02-01-2012, 08:21 AM
As the coolant gets hot ... or extremely hot... vapor is allowed to bypass pressure cap and vent into atmosphere. In a large volume system such as the Winnie has, this doesn't amount to much as the reservoir has a chance to add to the cooling of the coolant. But there is a bit of venting.

As the engine cools and the coolant contracts in volume, the pressure cap may vent inward ... or, the radiator hoses may collapse a bit (this can be observed) to make the volumn adjustment. All depends. But there is a period when this closed system goes slightly negative (to atmosphere) during the cooling phase.

Or so I think....

If you have the means to do a pressure test as you describe ... that should very imformative.

02-01-2012, 08:23 AM
I think Blackstone could identify engine oil vs tranny fluid in the coolant .... not sure they could pin point the leak if it is engine oil.

02-01-2012, 10:19 AM
I agree with 12Ounce analysis... the main period oil can be drawn into the coolant passage at the lower intake is during/after cool down.

However, there are no oil passages on the lower intake, but it acts as the cover for the balancer & lifters which do see oil. The oil on the lower intake therefore is mostly "splash" from the parts below.

I don't know if there is "high pressure" oil passing through the front cover. Does that occur where the oil filter/oil pump are located?

02-01-2012, 11:01 AM
....I don't know if there is "high pressure" oil passing through the front cover. Does that occur where the oil filter/oil pump are located?.....

IIRC: The pump is mounted directly to the front cover ... I can't remember, but think the pick-up tube is mounted to the pump. The oil pan extends beyond the short block to allow this to happen. The high pressure oil goes thru filter, then thru hole in cover and gasket into main block artery. (I think!!)

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