Radiator Resevoir Filled With Grey Gunk...

If a radiator fill resevoir is filled with grey foam-looking gunk, does that mean oil is mixing with the coolant? This car does not have a
radiator cap. This is on a 95 Saturn sedan. Will a flush fix the problem, or will it keep happening?
-supa
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If that is oil in the overflow reservoir, then the problems are more than a flush will correct.
Every radiator that I have ever seen had a removal cap of some sort or another. Maybe I just haven't seen one like yours, I guess.
Oil in the radiator can come from a leak from the automatic transmission cooler or from a leaking gasket, or crack, in the engine head area.
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Many of the newer cars do NOT have radiator caps. There is a pressure cap, but it's not always on the radiator these days. It does sound like the poster has a serious problem. If it's transmission oil from a leaky cooler, he could flush the transmission and fix the leak and have a chance of saving the transmission. If it's engine oil, he's in for a teardown there and a flush will not help.
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Agreed all above. Every radiator I have seen has had some sort of cap, but I am not exposed to as many variants as I once was.
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The '86-'89 Toyota MR2 radiator does not have a cap. The pressure cap is at the other end of the vehicle.
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If a cyl compression test shows good, then the problem would have to be related to transmission, right? (Supposing this thing has a transmission cooler--I'll have to check and see.)
The transmission has been acting up... hmmm :)
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Have you had the vehicle in for 'service' lately? One trick sleaze bag shops do is to pour some oil in the overflow tank to imply you need serious work like a flush, then when that doesn't 'work', a new head gasket, etc... That is especially sneaky on the closed systems where you can't check inside the rad itself....
I would clean the gunk out and then see if it comes back. It doesn't sound like you are losing coolant which could be a sign of head gasket issues.
I would be checking the engine oil and the tranny oil carefully to see if it looks milky or frothy. Water will make a milkshake looking oil. It will collect on the dipstick and on the engine oil cap.
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supafly wrote:

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a gray-looking "gunk" might be an over abundance of radiator stop leak in the system, just
might be, and / or oil that has tried to mix with the radiator coolant.
mho vfe
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on an aside, many radiators are 'sealed" systems, where the radiator itself no longer has a cap, but uses a stand-off reservoir instead. My '89 Eagle has no radiator cap, so the newer "sealed" systems go back at least around 15-16 years now.
However, almost ALL radiators have a drain plug at the bottom of the radiator, that may be what's confusing some of the prob. being spoken of.
Re the original prob., are you losing oil or trans. fluid? Are you checking those levels to see if they dropping more than normal for your ride?
In any case, flush the cooling system!!!!! Even if there is a leak, no sense in wasting your cooling system in the process!!!!
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