Mechanics

HEAD GASKET

1999 Volvo XC70 • 5 cylinder AWD Automatic • 120,000 miles

Is it foolish for a novice to attempt to diagnose/replace/fix a head gasket on a 1999 Volvo?
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Novice
November 24, 2010.



Yes, but it's not impossible. I sure would rather you learn on an easier car to work on. To diagnose a leaking head gasket, there is a tool that will detect combustion chamber gases in the coolant. It is a glass cylinder partially filled with two chambers of a special blue liquid. That liquid will turn bright yellow if gases are present.

The two most important things when replacing a head gasket are surface prep and flatness of the head surface. Surface prep means using a rotary air tool with a scuff pad to rough up the surface so the gasket will bite in and seal. The same pad can be used that you use to clean off carbon and old gasket material.

Older cast iron heads must be flat within.005" in any direction. For newer aluminum heads, that number is.002". You'll need a straightedge and a feeler gauge to check that. If you buy your gasket set and other parts from an engine machine shop or rebuilder, they will likely offer to check the flatness for you for free. It only takes a minute.

Warped heads can be milled to make them perfectly flat, but that is not an acceptable repair for heads that have overhead camshafts. Once the head is warped, so are the journals the camshaft runs in. Machining those heads does not address the out-of-line cam journals. Those heads must be heated in an oven and clamped down with shims to straighten them.

Some engines are "interference" designs meaning the pistons and open valves occupy the same space but not at the same time. When you install the timing belt or chain, rotate the engine by hand at least two full crankshaft revolutions to check for free movement. Every engine has special characteristics and procedures that must be followed. Don't attempt to do this without having the service manual nearby. It will list the steps to follow along with pictures or line drawings, and it will provide torque specs and tightening sequences for the bolts. It is very important to tighten head bolts in the proper order and to the proper tightness. Most engines require that to be done in three steps so the clamping forces remain even at all times. Some bolts thread into the crankcase or the cooling system. They will require a thread sealant. Some head bolts are "torque-to-yield" design. They stretch when installed and are only used once. You must replace them when replacing the head gasket.

Caradiodoc

Caradiodoc
Nov 24, 2010.
I also have a 1999 Volvo XC70, 5 cyl Automatic All Wheel Drive with approximately 120,000 miles. I have a warped Head by approx 0.012”. My Brother-in-law and I have stripped the engine down. We are mechanically inclined but are not qualified mechanics! This engine is over-head cam and so I am told that machining the head is not an option. The answer given to the above question mentions the possibility of heating the head to remove the warp. Can you suggest where I could go to get this done?

Neil.

Tiny
Sndouglas
Sep 18, 2011.
This question is a year old and belongs to someone else. If you need help with something, please create a new question of your own.

Wrenchtech
Sep 18, 2011.