I have a 1993 Toyota Corolla 1.6L with 200K miles. It is a sweet ride, but about every 2 or 3 years, the exhaust manifold cracks. I have replaced it several times, installing new gaskets, and carefully following the torque specifications on all of the bolts, but eventually, it cracks again. Can anyone help with advice as to why this is happening, and how it can be prevented?
@Murphgeek, all I can tell you is that it’s pretty common on the 1.6 4A-FE and the 1.8 7A-FE
It doesn’t help your situation, but at least you know you’re not alone
I would suggest that the OP verify that the original splash shields are still in place.
If one or more of the splash shields are missing, that could allow water from puddles to hit the extremely hot manifold when the car is driven in the rain. When cast iron is hot and is hit with some cold water, it is not unusual for it to crack.
The OP may even be able to fabricate a shield from sheet metal, and fasten it beneath the manifold in order to avert this problem.
Make sure the mating surface on the head is flat with a straight edge.
@VDCdriver for many years I had a 1995 Corolla with the 1.8 7A-FE
The exhaust manifold cracked and I replaced it, making sure to install all of the heat shields and properly torque all the bolts.
Approximately 1 year later I noticed that the replacement was cracked
I did not drive through many puddles, by the way
Where are you getting the replacement manifolds from? Same place? Also, if a better stock alternative is not available, there are tubular headers that can be bolted in place. They could solve the cracking problem, but they are known for working the bolts loose easier than the stock cast iron manifold. www.summitracing.com has some affordable ones.
Tom and Ray also mentioned on the show that a cracked exhaust manifold isn’t an uncommon problem on Toyota Corolla of this vintage. I think making sure all the splash shields – and all the parts that are supposed to be there for that matter and are installed securely – is a good idea.
@GeorgeSanJose it is a good idea, but it didn’t prevent my exhaust manifolds from repeatedly cracking
Design flaws occur with every car maker. Toyota is no exception.
You might take a cracked manifold and have it professionally welded up. The prior cracking may have relaxed the casting enough to where a welded manifold won’t crack again once subjected to heating and cooling cycles again.
Many a Gibson guitar has suffered a headstock crack and a proper repair job with glue makes them stronger than they were to begin with.
Are you replacing the exhaust manifold along with the updated heat shield? If not that’s the problem.
The updated heat shield has much larger openings over the original heat shield in order to allow the heat to escape from around the manifold.
Tester
I too have witnessed this phenomenon on a friend’s Corolla. Thank you, Tester, for advising of the updated heat shield. I can’t find any reference to it. Can you offer any link?
I don’t think the heat shield can be purchased seperately but instead as an exhaust manifold kit. http://www.partsgeek.com/catalog/1993/toyota/corolla/exhaust/exhaust_manifold.html
The reason I know about the updated heat shield is, in the 90’s when these manifolds were cracking there was no aftermarket source for a replacement manifold. The dealer was the only source. And when a manifold kit was aquired from the dealer it included the updated heat shield.
Tester
Thanks. Should my friend have to call me again she’ll think I’m a genius.
@Tester I replaced my original cracked factory manifold with the Dorman part you mentioned.
And it cracked too, so unfortunately I think Dorman is duplicating Toyota’s mistakes.
Or there’s something else going on.
@thesamemountainbike even if it doesn’t work out, your friend will still think you’re a genius for finding the part!
@db4690. When someone has repeated exhaust manifold failures on these vehicles you always ask if the updated heat shield was installed. If so, then the next thing to check for is a lazy O2 sensor.
These vehicles are OBDI engine management systems. So the O2 sensor"s function wasn’t as closely monitored as it is for the OBDII engine management systems. The O2 sensor cross-counts on an OBDI system could flat-line for as long as ten seconds before it would cause the Check Engine light to come on. But, if the cross-counts restarted again before that ten seconds elapsed the Check Engine light won’t come on. So let’s say the lazy O2 sensor flat lines at .7 volts for 8 seconds and then starts cross-counting again for 2 seconds. For that 8 seconds at .7 volts the computer thinks the engine is running rich so it leans out the fuel mixture. This then causes the exhaust gasses to become hotter overheating the exhaust manifold. Now depending how long the O2 sensor flat lines where it causes the exhaust gasses to be hotter will dictate how long the exhaust manifold lasts before it cracks again.
Tester
@Tester I checked my O2 sensor with a Fluke 88. It wasn’t lazy.
I strongly suspect that Dorman repeated whatever mistakes Toyota made with the exhaust manifold.
I have moved on and no longer have that car. That car actually had passed the smog with the cracked manifold.
One of my colleagues has an older GM truck. He mentioned that he had repeated cracked exhaust manifolds in the past. The permanent fix was to install headers!
The point here is that some problems can be difficult to fix and sometimes the solution is to look outside the box.
Something else to consider along with a potential design flaw is the consistency of the cast iron and how long, if at all, the iron was aged before machining.
A friend of mine here who is a retired machinist extraordinaire used to machine engine blocks and they also have a foundry on site where those blocks are cast. He told me once years ago that after those blocks were cast they were basically thrown out into a field and allowed to age for about 2 years before machining them; just like tomatos ripening on the vine.
This allowed the cast iron time to basically alter its shape due to repeated heated and cooling cycles in the weather.
Maybe those manifolds are not being aged much, if at all, before heading to the machine shop.
The same thing could apply to brake rotors and possibly explain why some may be more prevalent to distorting than others.
Just some food for thought anyway.