Water sound uder dash, missing coolant

[kimjett1]

I Have a 1991 Opel Kadett, that has a water sound coming from under that dash that is associated with accelerating, and has increasingly gotten worse.
We bought this car about a month ago...We had a leak test done on it because of the sound, and there was also some brown lumpy gunk in the coolant reservoir. It passed, and I haven't notice white smoke from the tailpipe,and the car doesn't overheat. I check the oil dipstick periodically to make sure coolant is not in there, and I also check the oil cap for a ring, so I am thinking this means no head gasket leak...
To clean out the gunk, and hopefully stop the sound, we did a coolant flush. While doing this we noticed that when the cap is off and you accelerate, you can see bubbles come up, which makes me suspect gasket leak again...When we refilled the coolant, it only ended up taking about 3/4 gallon. Over the past couple weeks, we have had to add another gallon and a half. It seemed kind of odd to have to add that much more, so I have been checking for leaks, and have found none. More of that gunk has shown up in the reservoir, but from the explanations I have seen online, I don't think it's oil.
Also, recently it has began to run rough when I start it up in the mornings.

[jd_975]

Hi, from your description you have classic head gasket failure symptoms, is the sound like rushing water on first start up and worst on the first few revs? I`ve worked on vauxhall/opel`s for a lot of years now and can say on 100% of the vehicles I have had with the same symptoms the head gasket fails dramatically within a few months of checking if it`s not sorted. Have you thought about getting a block test done? This basically entails running gas from the coolant reservoir through a special blue liquid which changes colour if there is CO (basically exhaust gas) present in the coolant header tank indicating a failure in the cylinder sealing i.e. the head gasket, most small garages can do this for you. Hope this helps