My 99 Nissan Almera has been sitting unused for a few months, and I just went out to start getting it up and running again. I noticed that the coolant in the reservoir was a bit low ( but clean looking ) and decided to check if the coolant in the radiator needed topping off. When I opened it I noticed this gunk around the filler neck and on the pressure cap:

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And here's a picture of the cap ( I had already started wiping it off before I thought to take a picture ):

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The truth is that if I was buying a car and I saw this under the radiator cap I'd assume there was a head gasket problem and not buy it.

I only had to add a tiny amount of coolant to top off the radiator, and I didn't see any evidence of foaming or frothing under the oil fill cap or on the dip stick. After starting the engine I had "white smoke" for a few minutes, but I'm guessing that it was probably just steam as the car's been sitting for a while and probably had quite a bit of water condensation inside.

I was planning on putting new shocks and brakes and going to pay the annual registration, do the annual test, etc.. tomorrow, but if there's a strong chance I may have a blown head gasket then I'll have to rethink all that.


Just wanted to follow up at this car is still going strong 2 years later.

  • No expert here, but from what I have been reading recently this can be caused by blown gasket, cracked head or worse cracked block. Apparently the location of the failure is the determining factor as to whether the oil will leak into coolant, coolant will leak into oil, or both. As for white smoke on start, I also read recently that sometimes a small leak can seal when the engine heats up and the components expand and prevent further leaking. Let the experts answer this though I have not read of any innocent way of oil going in the coolant except user error.
    – Chris
    Mar 15, 2017 at 17:03
  • @Chris I was also thinking that since it is a brownish-red color it might just be rust mixed with dryed out coolant that floated to the top. Mar 15, 2017 at 17:24
  • it looks like rust to me. do a chemical test or have someone hook up a gas analyzer.
    – Ben
    Mar 15, 2017 at 18:51
  • @Ben how could you do a chemical test on it? I was just thinking that maybe if it's rust it would be attracted to a magnet? Mar 15, 2017 at 19:16
  • sorry i meant a head gasket leak chemical test. i doubt a magnet would work, it might give it a try. or you could collect a sample and send it for analysis.
    – Ben
    Mar 15, 2017 at 19:19

1 Answer 1


The gunk seen here is a mixture of gel and rust. The most common cause of the gel is coolant over-concentration. The rust comes from corrosion of the inside of the engine block.

There is no definitive visual sign of a failed head gasket, they do not present any visual symptoms. Head gasket failure presents as CO2 in the cooling system as long as the affected cylinder is firing. Testing for this is done one of three ways. Use a gas analyzer, use a C02 detector, or a chemical detector test. If the cylinder is not firing then test for hydrocarbons in the cooling system with a gas analyzer.

To test the gel take a sample and put it in water. If it dissolves is likely gelled coolant. It does not it could be engine oil emulsified with coolant.

It if does not dissolve that could indicate a head gasket failure of the oil passage to cooling jacket type. On some engine designs this can also be a failure of the intake manifold to cylinder head seal. This type of failure is less common than the cylinder to cooling jacket failure described above.

  • I'm guessing the rust is probably from a few months ago when I ran water in the cooling system for a few days when I had to change the thermostat. But what might lead to coolant over-concentration? I use a pre-mixed Prestone green glycol coolant. I did notice I've been slowly loosing coolant, maybe some of the water is evaporating out / boiling off for some reason and that's causing the coolant to get too concentrated? Would adding a little distilled water to the radiator maybe help? On the head gasket issue, I thought oil in the coolant was a strong indicator of a HG problem? Mar 16, 2017 at 6:37
  • I've always used slightly over-concentrated coolant mix, I've never seen this kind of gunk build-up. I'd say this is more to do with a lack of maintenance and servicing of the cooling system. If it were my car, I would thoroughly flush the system with plain water using a garden hose forced into each hose/radiator/engine block opening (maybe even use a flushing product), clean whatever I could access with a brush, then fill it up with the correct coolant at the correct ratio. If you don't have other symptoms of head gasket failure, I'd say you're probably fine.
    – DizzyFool
    Mar 16, 2017 at 9:31
  • @RobertS.Barnes See my additional notes on oil leak type failures and a test for the gel noted in the photo. Mar 16, 2017 at 19:49

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