Mercedes: location, head gasket leak, upper radiator hose

Question
QUESTION: I have a 87 benz 420 sel i was wondering the location of the thermostat so i can change it. and where to find a repair manual

ANSWER: Dee,
I have a 1986 420 also. What are the symptoms?
Rob

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QUESTION: rob here's what up, the problem is the heater coil i can't get around to taking out the whole dash just yet so i disconnected the two hoses on the engine ( the inlet heat/outlet)and created a bypass (with one hose going from one side to the next until i can get to changing the heater coil)prob:the temp gauge reads 120 and the pressure build up is so great that the anti freeze leaks out of the pressurized expansion tank cap at the top of thecar I'm not sure if the thermostat is completely closed and if i removed it ,if it will solve this problem until i get around to changing the heater coil and going back to my original question where's the thermostat located top bottom middle?. any help would be appreciative

ANSWER: Dee,
Most likely the thermostat is set in the block where the upper radiator hose enter the bloc. The hose adapter held by two screws come off to allow changing of the thermostat and gasket. However, I would not just remove the stat without installing a new unit. The thermostat helps to maintain an optimum temperature for fuel economy and proper lubrication.

If the 120 is C that is too high of course, if it is 120 F then it it too low now, and removing the thermostat may not be the issue.
If you have a head gasket leak then you may be pressurizing the coolant and causing the back flow in the recovery tank.

If air pockets get trapped in the coolant circulation system you have hot spots circulating and than can cause engine damage.
The recovery tank is designed to allow any air pockets to burp out of the system during heatup and cool down cycles. It is important that the expansion cap on the raditor also work properly to accomlish the purging of air from the radiator.
Good luck
Rob



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QUESTION: rob whats the best way to find out if it is a head gasket leak,a pressure test?

Answer
Dee,
If you remove the radiator cap and crank the start and warm up the engine you should see the fluid circulating beneath the opening.
A leak will cause bubbles to rise to the top.
I also would run an compression check to make sure there is consistent reading for each cylinder.
Warm the engine up remove all the plugs, borrow or purchase a gauge with a hose and screw-in plug adapter for this engine. Some are vehicles are metric and some SAE. Our parts store should be able to tell you the threads, or take a plug to the store and ask.
with the gauge in place have crank the engine through about ten seconds of travel. Record the compression number.
Do this for each cylinder. If the reading are pretty close you are probably OK.
If you have one with low reading, it can indicate a leaking valve or bad rings thus the low compression.
Some time you will find moisture on the plug if it is sucking coolant back into the cylinder.
Just make sure the oil has on milky appearance. This would mean that the gasket has also blown to an oil journal and water and oil mix will fry an engine bearing.
Good Luck
Rob