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Larry, Automotive technical expert
Category: Car
Satisfied Customers: 1139
Experience:  30 years automotive technical writer, editor & author
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1998 Volvo V70: XC..the PCV Valve located on the Engine..oil leaks

Customer Question

Question is about a 1998 Volvo V70 XC -i) Where is the PCV Valve located on the Engine - ii)how to access it and Clean and Replace filter - iii)can this cleaning really help equalize backpressure in the engine & help reduce oil leaks ? Need advice and also need to know where I can get a repair manual cheap
Submitted: 6 years ago.
Category: Car
Expert:  Larry replied 6 years ago.
Your Volvo doesn't really have a PCV valve like most other engines. Rather, it is more of a box with a fixed orifice that vents the crankcase.


Here is a description of how this crankcase ventilation system works:

Crankcase gases are removed from the cylinder block (and cylinder head to an extent) to an oil trap (1) where oil is separated from the crankcase gases and returned to the oil sump. The hose to the cylinder head equalizes differences in pressure between the upper and lower parts of the engine.

When there is little load on the engine or when it is idling there is no under-pressure in the fresh air hose and only a small quantity of crankcase gases are formed. Because of this a vacuum hose (7), to lead crankcase gases directly to the intake manifold at low loads, goes from the heating nipple to a calibrated intake downstream of the throttle.

The heating nipple is calibrated to provide a controlled flow of crankcase gases. Power to the PTC type nipple is supplied by the engine management system main relay and prevents water vapor in the crankcase gases from freezing in the fresh air intake hose at low temperatures.

The PTC nipple temperature stabilizes at approximately 80°C (176°F) as soon as the engine is started.

If you engine is leaking oil, it is likely because the seals are old and have shrunk. I would recommend changing the oil and using a "high mileage" oil designed for cars with over 75,000 miles on the engine. Valvoline is a good brand. The oil contains additives to help older seals swell and regain some elasticity. That should help slow down or stop the oil leaks.

As for a "cheap" service manual, try ebay.
Customer: replied 6 years ago.
My question part II ii)how to remove or clean & replace - not really addressed
Expert:  Larry replied 6 years ago.
The VOlvo service literature does not say specifically how to remove, nor is there any recommendation for cleaning it.

If you think cleaning is necessary, it appearssoaking it that the unit pulls off the hoses. It might be possible to clean it by spraying throttle cleaner into the openings. But I doubt this would do a very good job. You would probably have to replace it with a new one.

A similar setup is used on certain Ford engines. Ford has no recommended service intervals for their crankcase breathers, and no cleaning recommendations.

To check whether or not the vent is flowing air, pull off the hose that goes to the cyolidner head (#2 in the illustration) and feel for vacuum while the engine is idling. If you feel no vacuum, the orifice inside the box is plugged and it needs to be cleaned or replaced.

If this answers your question, please ACCEPT now. Thanks!

Larry, Automotive technical expert
Category: Car
Satisfied Customers: 1139
Experience: 30 years automotive technical writer, editor & author
Larry and 17 other Car Specialists are ready to help you
Customer: replied 6 years ago.
Reply to Larry's Post: Larry , Automotive Editor, Expert, If you have any more specivfic information about where this oil trap is, I looked for it pretty exhaustively and unless its UNDER the outside curve of intake manifold - I have know idea where it is or how to get at it
Expert:  Larry replied 6 years ago.
Are you saying it is not lcoated in the illustration above that I sent you?

If the illustration is incorrect (which I got direct from the Volvo service literature), or you have a non-U.S. model vehicle, try this:

Find any hoses that appear to be vacuum hoses or vent hoses that are connected to the engine valve cover. On one end or ther other there will be either a PCV valve or a fixed orifice oil separator breather.

Also, look in your vehicle owners manual under MAINTENANCE, EMISSIOIN CONTROLS or PCV and see if anything is listed.

Expert:  Larry replied 6 years ago.
One of our other experts passed along the following info, so I am forwarding it to you:

The oil separator/breather box on your engine is located under the intake manifold.

Removal of Intake is neccessary to get at it.


Hope this helps.

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