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Replacing just the head gasket vs. complete overhaul after overheating an engine?

My daughter’s 1999 Subaru Outback Limited threw a water pump but she kept driving until it overheated. Replaced water pump but the head gasket blew next. Not knowing how hot things got while the pump was out, I’m thinking maybe there are deeper issues lurking beyond the head gasket… how can I know for sure? The mechanic wants to replace the gasket with the engine out - if it is already out, does it make sense to do a complete overhaul?

When a car overheats and you keep driving it’s usually game over for the engine. The wife of a friend did just that.

The engine needs to be thoroughly checked out; compression, leak down test, etc. It may cost you $200+ to find out it’s toast, but by some stroke of luck, it may be savageable.

I would vote against an overhaul. In times past, when engines weren’t built to such a close tolerance, the “overhaul” often amounted to grinding the valves, honing the cylinder walls, fitting new piston rings, and replacing the bearings with slightly undersized bearings. With today’s engines built to verry close tolerances, a remanufactured engine is, in my opinion, the way to go if the engine needs to be replaced.

I’m with Triedaq on this one. Once the head comes off, both the head and its corresponding surface of the block can be inspected. If the head isn’t warped (warning: it likely is warped), then you might even get out of this reasonably…albiet not cheaply.

A complete overhaul IMHO would be overkill. While overheating is not good for the engine, typically the “short block” (everything from the head down) will not be damaged, as it would were she to run it without oil.

Good comments - thanks. One wish I have is to figure out salvagability before the engine comes out. The car is at a Subaru dealer and I assume they diagnosed the blown gasket through a compression or vacuum check. My thought is that any other condition that such checks could find would be masked by the blown gasket. Perhaps there is a way to scope the condition of the cylinder with a camera pushed through the spark plug hole? The only other indicators I have are from my daughter. When she realized the overheat condition, she stopped the car. After the water pump was replaced, she drove it a week before the gasket blew, and when it blew, it was obvious from the steam - but she thankfully didn’t allow the temp gauge to go high again. No roughness beforehand, no skipping, no hesitation, no burning smell, no oil leaks, and the car can still start and run. I like the thought that the short block is OK if the oil was still in place… I wouldn’t like a warped head, but that is better than say a cracked block.

There’s really no way to assess the damage without pulling the head. There are fiberoptic scopes called “borescopes” (for checking inside a bore…or for use by a boring mechanic), but they’ll not be able to determine anything useful. The head needs to come off.

But I feel safe in saying that you can feel comfortable that the damage if any will be restricted to the head.

What should be done is that a compression test should be performed before any engine disassembly is done. This can reveal whether or not a piston ring problem exists and if this problem is present one will know that a complete overhaul is necessary.

The word “gasket” is used in the singular. When it comes to a Subaru one always replaces both gaskets; never just one. The heads should be checked for flatness and will likely need to be resurfaced as warping is common. After 500 miles or so on a fresh head gasket job the head bolt torque should be rechecked.

I respectfully disagree that an engine can’t be properly rebuilt by someone and have it last as long as a factory new one; if it’s done right.
I’m also curious about what part of an engine does tighter tolerances apply to.
One can compare bearing oil clearances, piston ring gaps, piston to cylinder wall clearance, crankshaft end play, valve stem to guide clearances, etc, etc. and a 2006 model is no better than a 1986 or 1966 or even a 1956 model engine.

Mr OP (the one that wrote this post). you are the first of our readers that I can remember that ever asked this question and I say “good for you”. You are correct in your belief that an engine that overheated due too a failed gasket may have suffered so much damage that it is no longer a candidate for the “less” all the way around route for repair, it may require the “more” all the way around route.

Now we go to just what to do so your daughter has a car. For us (me) to tell you the best route we need to know more about the rest of the car. My inital "right out of the box’ thought is that this car is old enough and the damage is great enough that you should sell it for parts and get an entirely different car.

If you insist on working with this car I say have the engine pulled,disassembled and all the parts looked over. I will leave it to you to add up the cost of this versus a used very low mile engine (is that even possible I wonder)

So there are three choices, different car, used engine, fix this one right. There are quite a large amount of variables that only you know in order to make this decision. The person with the best idea about what is going on is that mechanic that has his eyes on things and I hope when you used the word “gasket” in the singular form it was a typo.

I do realize I have left a "patch job’ out as one of the choices.

Subaru engines are pretty tender…It doesn’t take much abuse to kill them… Aluminum engines in general do not take kindly to overheating…The car is 12 years old, maybe it’s time to move on…

Usually, I would recommend installing a used engine from a salvage yard, but with a Subaru, finding a decent one may prove difficult…For a while, you could find used engines imported from Japan where they total cars for almost any minor accident and they are not permitted to sell salvaged parts…So they export them to the ready market in the States…See if you can find one. I feel that any attempt to rebuild your engine would be disappointing…

For purposes of my original post, I judged the rest of the car as good enough to where I can disregard the other non-engine issues in making a decision. What does influence me is whether I get a good return in more time and miles if I repair the engine as that cost swamps everything else. Being a bit simplistic here and assuming I have a mechanic I really trust, if the repair cost equals the blue book value of the car (~$7,000), I’ll still repair the car - under the theory that you should stay with the devil you know, rather than with one you don’t. I much less would buy a used engine for the same reason ? and for the fact that I can?t start one of those inside a crate, whereas I can at least start a used car that I?m considering to buy. I would agree that the breakup value of the car is higher than blue book, but to capture that value requires you to manage the sale of the parts ? and if I could do that successfully, I wouldn’t be writing posts like this. So that pretty much leaves me with going with a rebuilt engine (~$5,000 for a Jasper long block not counting installation) or repair (~$2,000 to replace, yes, both head gaskets and machine the heads, if that is all that has to be done.) There?s another choice, which is to do the work myself ? possible, but I work on jet aircraft which would pays a higher return on my time than performing a DIY car repair like this. BTW, many jets dating back to the 60’s and 70’s still fly with owners doing overhaul jobs. The economics just seem to work. Cars on the other hand don’t lend themselves to straight-forward decisions like that, so I guess forums like Car Talk will continue to buzz with these discussions…

Considering everyone’s replies and my knowledge about the car (see my earlier reply), I have confidence enough to think the heads and head gaskets are my only culprits to deal with and there seems to be enough successful collective experience dealing with those to authorize starting a repair - aluminum engine or not. Yes, I still run the risk with something more? and to be sure, I?ll quiz my dealer about whether all the compression checks and other tests that could be run are done before starting work. If risk becomes reality and more is found, I could stop the repair in the middle for hopefully less than $2,000 and get rid of the car. Or maybe haul the thing home and my son and I will start a fun adventure of disassembling a car for the heck of it (cost = priceless) and find a way to sell the parts (eBay anyone?)

I’ll update this thread as the repair progresses. Good discussion - thank you all.

If you could put a real number on just how much driving was done with the needle in the red it would help,what do I mean? you have decided to go your own way no matter what. One last thing did this engine get so hot that it smells like they are taring the roof of the building that the car sits in? never a good sign. Do not ever and I mean ever, compare anything dealing with airplanes to anything dealing with automobiles,worse that the classic “apples and oranges”

This is another case of needing eyes on to determine the best route. I hope you have a competent mechanic and you trust him. In general, if you have less than 100,000 miles on the engine, a head gasket only is a safe bet. Over 200,000 miles and the rest of the car is in excellent shape, get a reman from a good reman company. If it is not in excellent shape, then junk it and get a newer vehicle. Between 100 and 200k, it could go either way.

The issue about piston ring damage and possible crankshaft bearing damage (if the engine oil is diluted) still remains.

Often someone will surface the heads, replace the head gaskets, and then discover the car is an oil burner due to fried piston rings.

I could not see getting too deep financially into a 12 year old Subaru.

Since the engine is out of the car, you might as well do this right. Your mechanic needs to pull the oil pan and inspect the crank and rod bearings and journal surfaces for evidence of severe overheating. If this is not done, the engine may not last long with the new head gaskets. A few years ago, I replaced a cylinder head and gasket on a Jeep Cherokee with a four cylinder engine. It had been severely overheated more than once because the owner thought it could stand up to such abuse. The head had a dozen or so obvious cracks in it. Two months after replacing the head and gasket, the engine spun a (possibly multiple) bearing. Overheating trashed the bottom end. I suggest a thorough bottom end inspection, especially since the engine is out of the car already.

ok4450, I would prefer a more definitive answer on the rings before going too far into this. I’m fine with keeping the 12 year old as it is in otherwise good condition, but I want a line on the best route to fix the engine problem without too much wasted effort.

Will a compression and leak-down test work to reveal bad rings if a head gasket is blown? Or will the bad head gasket interfere with detecting bad rings?

Keith, it is in between, and my trust of the mechanic is TBD. The car’s condition is good enough to keep IMHO.

Do you have recommendations for remanufacturing companies that I can trust?

I have no clue how long the temp was in the red. No other smells were detected during the overheat, nor does it have smells now.

As for airplanes and cars, I always get confused…

A reasonable suggestion, although I wasn’t certain how much you could see with the pan removed from a Subie H-block.

Sorry to hear your experience didn’t go well.

Since the oil did not get so hot that the engine smells like a tar pot I am getting more comfortable with just doing a gasket on each side and running it. I was expecting you to say that the valve train was caked up with oil turned to tar from overheating.

How do you do a compression test with a blown head gasket?