I have a blown head gasket i believe. there is a yellow gunk substance in my oil filler and my dipstick is a dark yellow. after running the engine around town and let it idle, the gauge does not overh

If you have overheated your car recently, then you possibly have a blown head gasket. Take off your oil fill cap (with engine off) and inspect to see if there is a milky substance underneath the cap. If so, bad news- head gasket. You can also check the oil dipstick for the same substance to verify bad head gasket, but usually it has to be pretty bad (gasket) or driven for a while before exhibiting any signs. The oil fill cap is a pretty good indicator. With the car cool, you can open the radiator cap and look and smell for anything other than coolant (fuel smell or oil slick). If so, probable head gasket.

You need to check the oil and see if the dipstick shows overfill on oil or if you see the white milky substance on the dipstick you may have a blown intake gasket or head gaskets. I would think it sounds like a blown head gasket. Hope this helps.
If you are adding water to the system you have a problem somewhere you might want to run a compression check on the cylinders to see if you have a intake gasket leak or a head leak. How hot did the car get because you might have cracked a head. If you don't see the water in the oil it may be exhausting out the tail pipe.

White smoke is usually a sign that there is a problem with the cooling system. Blue smoke is fuel related.
Have the cooling system checked at a guess I would say this is water leaking into the cylinders which indicates a cylinder head gasket fault. A faulty cylinder head gasket would also cause slight loss of compression which could explain the loss of power. remove the oil filler cap on the engine if there is a sign of a light brown (cream) coloured substance (water contaminated oil) on the cap or in the cover then the head gasket needs replacing also check the dipstick.
Hope this helps.

Do you have water or a white milky substance on your engine oil dipstick? If you do, then you have a blown head gasket. If not and if it is REALLY oil then you are in the beginning stages of a head gasket failure; the best time to catch and correct the problem. Change the head gaskets.

You have a blown head gasket. Water is bypassing your head gasket and has mixed with your oil. Take to your mechanic, will have to resurface cylinder head, new gaskets, water pump, timing belts.

this is coolant mixing with the oil it creates the off white gunk. you may have a head gasket leaking. does it blow white smoke? the intake may have a leak as well. need to find the leak and repair it to stop this mix from happening. a good shop should posses a dye test system to pinpoint the actual leak source. hope this helps

The white creamy solution is oil mixed with water. Take out your dipstick and check for the same substance, if so, you have a blown head gasket. If not, it's just condensed water in your valve cover that mixes with the oil, witch isn't really a problem. Have a nice day!

Replace the head gasket or get the block checked for cracks

Often (but not always), a blown head gasket will also cause deposit of water on a piece of cardboard held an inch from the tailpipe output while the engine is running (when this is happening, it is likely that the catalytic converter has been ruined and the muffler will corrode in short order as well).

Sometimes drops of water will be seen dropping from the end of the tailpipe. Another clue: turn on the heater; often when the head gasket is blown an odor of antifreeze and synthetic rubber will emanate from the heater vents.
Many of the symptoms of blown head gasket can be caused by some other problem in the cooling system, without the head gasket being damaged. Conversely, other problems with the cooling system can cause a blown head gasket and/or warped head.

When checking for a blown head gasket, one of the most common tell-tale signs is a milky-gray ring around your oil cap. When coolant enters the engine oil through a crack in the head or through a blown gasket, it evaporates and leaves a milky ring around the oil cap. Another easy way to tell is to check your oil dipstick. Change your oil and pull out the dipstick. Make sure that you take note of how far up the dipstick the oil is. Top off your cooling system and fill your cooling reservoir to the top. Screw radiator cap back on and start engine. Run engine for about 20-30 mins. or until it reaches normal operating temperature. Allow engine to cool (engine must cool completely to get accurate oil reading!!). Check oil dipstick again. If the oil has a watery appearance and has risen noticeably up the dipstick, the you probably have a blown head gasket or a warped head. Also look for a dripping, sweet-smelling liquid coming out of your tailpipe. Any of the above symptoms could be the result of a blown head gasket. The easiest way to tell is with a compression meter. This replaces the spark plug and lets you know what compression each cylinder is running at. If your compression is abnormally low, then you have a blown head gasket or a warped head. (note: consult repair manual for appropriate compression of each cylinder.)

Wankel Rotary engine guys no headers or gaskets

This milky substance does not affect engine performance or any other functions of the vehicle. During cold weather, moisture contained in blow-by gases (exhaust , oil, fuel, water vapor) is cooled by the intermediate housing wall and condenses due to difference in temperature. A chemical reaction between the moisture reacts and the engine oil in the intermediate housing will yield the milky fluid. This fluid then eventually dissipates
as the engine warms up to full operating temperature.

The milky fluid does not affect the quality of the engine oil and therefore the engine performance is not affected either. Mazda has verified that the amount of moisture in the oil is within the acceptable standard for motor oils commonly found in the market.

However, you should verify that the coolant reservoir is full and that there is no sign of engine coolant leakage.

You can also go to you Mazda dealer and ask for a new oil level gauge tube plastic insert which has been developed as a countermeasure to keep the milky substance off of the dipstick (however, the substance will still be in there- it's a cosmetic fix only).

Hope this helps