Preventing Head Gasket Failures

[chrispy]

I just picked up a 2000 Outback Wagon 5-speed last week, and am seeing a lot of info on the net about Subaru head gasket failures. Most common being 2.5L DOHC, but it's still happening (less frequently) with the 2.5L SOHC phase II engines. Apparently this problem was resolved in the 2003 model, but it is likely too early to tell.

There are so many reasons why head gasket failures can be problematic that there is no easy answer here. Several different auto-makers have experienced this problem in the last 10 years or so.

My last car was a 92 Saturn SL1 and I decided to go the Subaru route (for the AWD and the wagon) since the newer Saturns (and other GM's) have had serious engine problems.

My Saturn has 382,000 kms and no HG issues - EVER. The rocker gaskets are now leaking, but no engine problems to bitch about. All original clutch...mostly everything is still original. Only major failures were the wiper transmission assembly, clutch hydraulics, and master brake cylinder. Other than that, the car rarely saw a mechanic, except for regular maintenance. The Saturn is also a light and agile performer, which creates minimal load on the drive-train.

It seems that despite their reputation, Subaru is still having HG failures and rust problems. The HG issue could be related to several factors including faulty gaskets, engineering, manufacturing, hard driving, poor service, etc. Us Subie owners need to be prepared with a mountain of evidence which indicates that the HG issue is problematic in nature - should we become another victim. It might even be worthwhile to approach Subaru as a group to get action. Here in Canada, we have the APA - http://www.apa.ca.

Considering the apparent numbers for these HG failures (does anyone have a guestimate on the number of failures?), it appears as though the issue may be an engineering problem. I have read on the net that Subaru has replaced several 2.5L engines under warranty for severe knocking problems. Knocking/detonation, compression ratios, combustion temperature, and head gasket failures are all inter-related. The 2.5L engines have a 10.5:1 compression ratio, which is higher than normal. The back pressure of the AWD system, the immense weight of the car, accompanied with certain driving conditions (and styles, especially lugging) can put a tremendous amount of pressure on the engine.

I'm no engineer, but I believe the best method to deal with this issue is to do one's best to PREVENT the failure in the first place. The coolant additive fix that Subaru is offering is nothing more than a band-aid fix. At least they offer some extended warranty protection with it. How effective it will be...only time can tell.

Some interesting reading on PREVENTING HEAD GASKET FAILURES can be found at www.babcox.com/nascartech/np50320.htm. According to this article, one of the major problems for head gasket failures is improper load on the gasket. Their are a number of factors which can cause this problem - see the article.

A few tips:
1) Check fluid levels regularly.
2) Check for HG leaks regularly.
3) Watch temperature gauge when driving, especially in hot weather.
4) Use the highest octane gas available.
5) If your engine has consistent knocking problems, have it checked IMMEDIATELY, as knocking/detonation issues cause increased compression which can lead to HG failure.
6) If your engine persists on knocking after using high octane fuel, check the plugs. If they're yellowing (see the back of a Haynes manual for plug diagnosis), try colder plugs - this will lower the combustion temp. and aid in knocking issues and help stabalize compression.
7) Have your sensors tested during tune-ups, especially for the EGR system, as EGR affects combustion temperature.

Some other possibilities...

I blew the head gasket on a 1987 VW Vanagon/Westfalia. A VW mechanic told me that with the aluminum head engines you need to peform a coolant flush every 30,000 (better to do it every year before winter) in order to prevent the corrosion inhibitors from breaking down and leading to an HG failure. The VW problem is known as 'crevice corrosion'. I don't know if this is the case with the Subies though. You can read more about the VW problem at http://www.vanagon.com/problems/head-leaks.html.

More reading about coolants and corrosion at http://www.vanagon.com/info/articles/coolants.html.