TTAC Commentator spitfire writes:
Really enjoy the Piston Slap series. How can you tell the difference between a bad head gasket and warped block or head? I guess I’m not fully respecting the tight tolerances involved here because it would seem to me that once fluids start intermingling its way beyond a gasket to fix the problem. Thanks, keep up the good work.
Sajeev Answers:
Unless the car has well known fail points, like the Mark III Supra discussed in a previous Piston Slap (LINK: https://www.thetruthaboutcars.com/piston-slap-essex-archaeology-scorched-earth-supras/), there’s no way to know which part is at fault. Even if someone only “lightly” overheated a motor, it’s possible they are delusional and actually warped a cylinder head in the process.
Unless you own a late model I-6 BMW known to wiggle like a Daschund when it’s fragile cooling system bites the dust, or a Cadillac Northstar known to ooze fluids from every orifice, most signs of a blown head gasket happen in older vehicles. More to the point, a car that’s not especially valuable. If so, scrap the vehicle or do it right for the long haul: remove the head, take it to a machine shop, and replace the head gasket/bolts upon reassembly. Some cars have junky head bolts (Northstar, again) and others are torque-to-yield, so they must be replaced once you pull them out.
But wait, there’s less! If the head is warped and the car is obviously suffering from cooling system neglect, check the engine block for warpage too. Test every metal part, replace the gasket and replace the attaching hardware if needed. There’s simply too many labor hours involved to NOT do this repair right the first time.
Bonus! A Piston Slap Nugget of Wisdom:
If you aren’t the original owner, you’re in for more painful what-if scenarios. Perhaps the car overheated before, busted the head gasket, warped the head and the previous owner put Engine Block sealer (like Bar’s Stop Leak) in the system to band-aid the problem. Which we discussed before from the other perspective (LINK: https://www.thetruthaboutcars.com/piston-slap-morality-and-the-blown-head-gasket/). It happens!
Send your queries to mehta@ttac.com
My uncle had the head gasket issue with his 3.4 DOHC Cutlass Convertible (just recently BTW, he loves to have something different as his daily driver.) He made a partial swap (+cash) with his cousin who owns a body shop for a salvaged Monte Carlo SS with a 3.8V6. His cousin is going to stick an old 3.1V6 in the Cutlass and give it to his kid.
With head gasket/warped head or block issues, you’ve got to know when to fish or cut bait. Your almost better off to rebuild the engine entirely if you really love the car.
I just redid the headgaskets on my Subaru EJ25 DOHC engine. I bought the car on the cheap knowing they needed replaced. Once I got the engine apart it turns out only 1 side was bad and it was pretty minimal leakage between a coolant port and an oil port, but was bad enough that the overflow container had a slick lining of oil in it.
I took a crappy video with my cell phone to document the damage.
http://www.youtube.com/watch?v=Eo8YjPJQTKY
For some reason, the audio was purged from the video, but you can see where I’m pointing to the corrosion on the gasket which caused the leak.
Since I had everything apart I had the heads milled, which wasn’t really necessary since they were flat, but the corrosion between the ports had some pitting which I wasn’t sure about. They cleaned out the valve ports while I had the heads in too.
Here’s a better picture:
http://img830.imageshack.us/img830/4688/headgasketcorrosion.jpg
I’ve ran the car for about 2 weeks now and the oil is clean and so is the coolant, so it was a bad gasket. I hardly ever hear of Subaru heads getting warped.
I recently bought one of those late model BMWs with an I-6… hoo boy. I was lucky or unlucky, depending on how you look at it. I had those BMW cooling blues (actually reds, but who’s counting?), but lucked out that the head and gasket were okay.
Those I-6s are sweet engines. Hate the cooling issues.
You are lucky, quite lucky.
EDIT: kudos to you for noticing the problem, those who don’t monitor temperature gauges regularly usually fall victim to this problem on I-6 BMWs.
Not even late model. My 1992 325i was a constant cooling system nightmare here in the Southwest. Even if you notice the temperature gauge climb, you have less than a minute to shut it down. Frangible plastic water pump impellers, exploding pressurized overflow tanks, nearly impossible to change heater hoses, and the list goes on. Add to that a 29psi pressure cap and 206F thermostat and the stage is set for disaster. Oh, and it is the “blues”, special blue coolant, that is.
You are 100% correct. The key to a long lasting BMW I6 is to change all of the cooling system components every 60,000 miles or 8 years. The expansion tank is a particular weak spot. The temp gauge on a BMW is buffered, so the second it starts rising you HAVE TO pull over and flat bed it, or the engine will be finished and you will be a time-sert customer or worse.
Why would anyone buy a car that needs all of it’s cooling system components replaced every 60,000 miles? When I sold my old ’76 F150 years ago, it had 187,000 miles on it with the original radiator, water pump and heater core. The only cooling system parts that I replaced were the heater hoses and the upper radiator hose. The lower hose was original too, believe it or not.
How can you tell the difference between a bad head gasket and warped block or head?
A bad head gasket alone will leave the head and block still straight. A warped head or block can be measured to verify that they are warped. The engine rebuild specs will have a maximum dimension for warp, which is often on the order of about 0.004″ over the length of the head.
The gasket, head, and block surfaces can all be fixed for warp, but there are a host of other problems that you could encounter. A warped block will also have misaligned piston bores and possibly the crankshaft bearing journals, so machining them should be considered.
In addition, having water mixed with the oil is a Bad Thing, so it’s possible that damage has occured to every moving surface in the engine if the leak has gone on very long. You could get a sense of this by pulling the oil pan and a main or rod bearing to inspect for excess wear given the engine’s mileage.
So, the best approach may be to verify only a bad gasket, or do a whole engine job if there is any doubt. In-between measures may not work out.
Honestly I’m surprised that head gasket failure are not even more common on the iron block, aluminum head combination which still remains strangely commonplace. The different thermal expansion rates of iron and aluminum combined with the temperature extremes seen in engine operation are certain to put a great deal of stress on the head gasket which is stuck between the two.
That’s why they developed Multi-Layer Steel (MLS) head gaskets. They can withstand the “scrub” of the dissimilar metals without failing.
Been limping around a GM 3.4 with a bad head gasket for close to a year now. It is a “good” leak, if there is ever such a think as the exhaust gasses are leaking into the coolant and no coolant is getting into the oil. I have to “burp” the coolant system every few hundred miles and not get caught in gnarly bumper-to-bumper traffic. For running around town and basic errands the beater still meets my needs. Considering using the sealant route, but figure then the engine would be good for one year tops and then its finished.
What was that “old trick” to eke out a few more miles?
Drop a raw egg into the cooling system or was it oatmeal?
Add a side of bacon?
An egg in the radiator will stop a leak in an emergency, but not a bad head gasket.
Warped blocks are extreamly rare. It takes an over heating situation to warp the head, but have it checked for sure. Surfaceing the head is not expensive. Chances are the machinest will talk you into doing it, he has a boat payment to make!! On some diesels (early 5.7 GM) the gasket would allow a small amount compression to enter the cooling system, the first sign was the heater stopped blowing hot air, but you could drive this way for weeks before you had to add more coolant.
I have had to do head gaskets three times on my elderly Explorer. It’s never been an actual problem with the iron block and heads, but just bum gaskets.
Of course when it needs head gaskets, it’ll need a heater core, and then a radiator in about 12 months time after that.
truck runs great and drives and looks like new, but will go through a complete cooling system change every 3 years.
“How can you tell the difference between a bad head gasket and warped block or head?”
The bad head gasket is a thin thing the looks like cardboard and has four or six big round holes in it. The warped block or head is a big hunk of metal.
Had a friend who went through this on a second-gen Acura Legend (another known-problem-car Sajeev), and swayed me away from buying one. The thing with those is they usually pop the gasket at the #3 or #6 cylinder, and just burp exhaust into the cooling system. After a while (and some neglect) the motor overheats and it’s a goner. The supposed best solution if the heads warp is to get new ones, since there’s little to shave from them. Same for the block. And swap the hoses, heater core, radiator etc while you’re at it. The only good thing about this, it led to the 3.5V6 swap from the first-gen Acura RL.
Northstars, stud the block and do a full gasket job. Drive it another 100K.
A key to the high mileage club is to prevent overheating in the first place. Change all the hoses, t-stat, belts, etc on a schedule and you are usually not going to be changing a head gasket. Still, some engines will take out a gasket anyway. Pretty much all brands have (had) a weak engine in their portfolio. Should you be faced with such a problem, it is important to check the head and the block as already stated. I can’t emphasize enough the importance of replacing the head bolts. Many are TTY and will not provide a proper clamping force after being in use. Also, I always used a proper thread lube like ARP when doing a head job. And watch the torque sequence.