Mike's Corner

Mike left the dealership network in 1999 to start Smart Service. He wanted to get back to the basic premise of a face-to-face relationship between the customer and their mechanic, which just wasn't a possibility at the dealership level. Mike is currently certified as an ASE Master Technician and has over 13 years of prior Subaru dealership training and experience. He has over21 years of overall automotive experience and attended the Shoreline CC Automotive training program in 1985. 


Head gasket problems...

Why’s my car overheating? 

We can help! 

Smart Service prides itself on turning what otherwise seems to be a bad situation into a good one. Over the years Subaru engines have been some of the most reliable in the industry. As of late some of us have been disappointed in an increased amount of head gasket related problems on certain late model Subarus. Although the head gasket failure on a Subaru may not be a terminal problem in and of itself, failing head gaskets can lead to much greater engine damage if not caught in the early stages. 

Statistically at our shop, head gaskets on the Phase 1 2.5 liter engines have a higher failure rate than any other Subaru engine we work on. These engines were common in the 96-99 Legacy Outback, Legacy GT and 98 Impreza RS. Warning signs to watch for include discoloration of coolant in the recovery bottle (black or sooty). Coolant that smells like engine exhaust or engine oil, unexplained loss of coolant without obvious external coolant leakage is another indicator that the head gaskets may be failing. 

Often we hear the story of someone that is trying to figure out why their Outback randomly overheats, they’ve replaced the thermostat, radiator, coolant and the overheating problem still persists. 

One of the head gasket’s functions is to keep the forces of internal combustion inside the cylinders of the engine while allowing coolant to circulate around the cylinder walls and oil to circulate between the head and the block. When the gaskets are starting to fail, some of the combustion gasses (exhaust usually) are forced past the thin metal head gasket into the cooling system. Little by little these gasses accumulate in the cooling system and begin to create an “air pocket” if you will, inside of the engine cooling system. Depending on where this air pocket circulates to, or how large it is, it can create numerous issues. If it becomes trapped around the water pump or thermostat it can prevent coolant from flowing through the engine, which results in almost immediate overheating. 

Early detection is the key to minimizing damage beyond the head gaskets themselves. Overheating an aluminum engine can result in warped head surfaces, warped block, cracked or damaged cylinders and even damaged pistons in an extreme case. The flat surfaces that the gasket is sandwiched between are the cylinder head and the deck of the engine block. If these surfaces become warped beyond allowable limits the expense of the repair increases. Warped heads can usually be machined for a couple hundred dollars but if the deck of the engine block is warped or cylinder walls are damaged it could necessitate replacing the engine block which can add $2000-$3000 to the repair. The good news is that even on the engines we encounter that we know have been overheated, rare is the case where the block needs replacement. 

How does one know for sure? Well there is no foolproof way of knowing what exactly has failed until the engine is disassembled. Our method is to use an exhaust gas analyzer (similar to what is used at an emission test station) to “sniff” the radiator and coolant recovery bottle for exhaust gas (hydrocarbons or HC’s) content and concentration. A cooling system should have 0 parts per million (ppm) in the cooling system. In the early stages we might detect 10-40 ppm HC’s. These usually are the cars that haven’t overheated yet because the amount is still so small. When the numbers get to 45 ppm and above it indicates a more active process going on. Beware that sometimes soon after a head gasket job a trace amount of HC’s can be detected but is no cause for alarm. Since you can’t purge or drain every single pocket/passage of the engine’s cooling system it may just be a residual amount that will dissipate. 

If you don’t have the luxury of a 4 gas analyzer you can purchase an engine block leak detection kit from your local NAPA autoparts store. Part Number 700-1006 for under $50. This kit uses a fluid that changes color when it chemically reacts with coolant containing exhaust gas. 

Now for the good news... First of all, our experience has been that once the head gaskets have been repaired properly with latest version of genuine Subaru gaskets, we haven’t seen any repeat occurrence. Since 2000 we’ve seen the part number for the head gasket supersede 4 times. Although Subaru hasn’t issued any statement on why these numbers were superseded, our opinion is that it was an improvement over the original part. The other good news is that with this latest gasket revision we have yet to see a repeat failure so it seems to be doing the trick. 

Keep in mind a lot of other beneficial things occur when performing a head gasket repair. Many of the seals and gaskets on the engine that may have eventually leaked will be replaced during the process. The oil and coolant are changed. The timing belt, water pump, and timing belt tensioner pulleys can also be replaced at a fraction of the cost while everything is apart. Also I have to stress that where ever you have the work performed, make sure the car is thoroughly evaluated for any other potential issues before authorizing the work. The last thing you want to do is spend you hard earned money for the repair only to be told that, “by the way Mrs. Jones, after we finished we noticed you will also need to replace your brakes in a couple of months and your clutch should be replaced soon.” 

All in all, I still believe that even if you must cross the head gasket repair bridge you still can have many reliable miles ahead of you. I can’t give you any advice on how to prevent it from happening. I’ve seen the most meticulous owner that has an exemplary service record have a failure at 65,000 miles and on the other end of the spectrum a person that nearly runs the car into the ground and still hadn’t had failure at 175,000 miles. Go figure huh? All I can tell you that if it does happen to you, I do understand your frustration and believe me, you’re not alone. Remember, you probably couldn’t have done anything more to prevent it. 

UPDATE: 2/24/2012 

Some questions have arisen from this article and I’d like to update you. Back in 2005, I wrote this article to help Subaru owners diagnose if they may have a head gasket issue. At that time I recommended Genuine Subaru head gaskets because I believed they were the best option available to a Subaru owner at that time. Between then and now a new aftermarket gasket has become our gasket of choice called the Six Star head gasket. You can read more about them on my blog: 

Which Head Gasket Is Best For A Subaru? 

Mikes Sig