MACS Service Reports - 2016 - JAN2

techinfo.Subaru.com

essary because some cars are just that difficult.
Unfortunately the results were the same, and this time the
shop pulled the water pump (an unlikely cause of the symptoms) and it looked fine. Flow through the radiator seemed
normal, and infrared thermometer tests indicated a normal and
smooth temperature drop from radiator inlet to outlet. The system also held pressure, so what now?
The technician then went through the head gasket checking
routine, starting with a look for bubbles in the reservoir, followed by use of the color changing type of combustion leak detector. We've always had good luck with the color change setup,
although some shops insist that many combustion leaks occur
only under load and this detector doesn't pick those up.
When neither gave a positive result, the shop pressurized the
cooling system, removed the spark plugs one at a time, turned
the engine over by hand to top dead center for each cylinder,
and using a plug hole adapter, pressurized the cylinder. The
technician saw that the pressures held, and there was no rise
in coolant level or bubbling in the reservoir. The previous shop
with the Mazda 3 went for an overnight test and even then only
saw a small amount of coolant in a cylinder, so the time may not
have been adequate. We prefer the test on the Mazda 3 overall,
because of the possible difficulty and error factor with closing
the valves on late model cars with variable valve timing.
However, with this case there was an important clue: the
head gaskets had been replaced with aftermarket gaskets just

Figure 3: Rubber sealing bead damage also shows on cylinder block.

techinfo.subaru.com

over 10,000 miles before, by another shop, to correct an external
coolant leak. That other shop used a name brand aftermarket
multi layer steel gasket. On the theory that something may have
gone amiss with the previous job (it had run out of ideas), the
shop pulled the engine, took off the cylinder heads (one very big
gamble, we'd say), but he did find leakage at the gasket joint at
cylinder No. 1 (driver's side front).
There is a tendency to blame the aftermarket parts, but we'd
be more likely to attribute the failure to clean deposits from the
bore-sealing portion of the head or block, head warpage and/
or re-use of the cylinder head bolts. Subarus are intolerant of a
rather small amount of warpage and failure to remove carbon
deposits from the head and block at the bore sealing areas and
rubber residue affecting the coolant sealing areas. See Figures 1,
2 and 3. If the previous shop didn't have the head resurfaced at
a first-rate machine shop, that could easily account for the short
life. In this case the technician did get the head machined, carefully cleaned the top of the block (Figure 4) and used an OE gasket, along with a set of brand new head bolts torqued to specifications. Result: good heat, no coolant overflow and a customer
accepting the premium price of the job.

techinfo.subaru.com

Figure 1: Deposits formed around cylinder sealing area of head and
block (head shown) must be removed carefully from Subaru 2.5-liter
engine.

Figure 4: This is what a cleaned cylinder block around cooling system openings looks like.

ANOTHER ERRATIC HEAT PROBLEM
Here's a heating issue with a minivan that has a
rear HVAC system, and the air blowing from the
outlets was cold. Okay, this happened in midwinter,
but the coolant temperature was about 210°F, and
so why would you even think about changing the

Figure 2: Damage to rubber sealing beads on cylinder head will affect cooling
system sealing and allow leakage between the cooling system and cylinders.

January 2016

MACS Service Reports

http://www.motorcraftservice.com http://www.motorcraftservice.com http://www.techinfo.subaru.com http://www.motorcraftservice.com

Table of Contents for the Digital Edition of MACS Service Reports - 2016