These engines blow head gaskets because they need cooling time before you shut off the engine
When you shut it off, If you hear creaking metal sounds there’s your head gasket getting destroyed
it only needs 30 seconds to cool down. Lower the idle and wait 30 seconds
yes a design flaw but easily avoided
It certainly is a design flaw and a refusal to fix it by adding an extra head bolt even if it would extend its tip slightly into the intake runner. I actually think we could probably drill and tap one and solve this problem but never really looked into doing it.
I will also agree that it is certainly a heat and cool down issue but I am not convinced that there's anything we can personally do to prevent it or extend the life of the head gaskets and I'm not convinced that idling the engine down for 30 seconds or even 3 minutes is going to benefit anything.
I'm not 100% saying you're wrong but I'm saying without testing and evidence we have no way to know and it's just a theory you have. I have a lot of those theories too from years and thousands of mowers and engines that I've worked on but it doesn't make all of them right. LOL
You could start with a non-contact thermometer to check some temperatures because I'm not convinced that an engine actually cools off when you idle it down but there's no exact linear action is the problem.
There are engines out there that when you're running them at their full operating speed actually run their coolest and they will heat up when you lower the speed especially after they're up to temperature BUT here is the real catch..... When you finally do turn the key off does the non running big aluminum heat sink block of an engine sitting there get hotter if it was at full running speed before you turned it off or if it was at a lower idle speed before you turned it off?
There is NO question it gets hotter either way but which way keeps it the coolest?
Also, other variables like oil level which can have quite a difference from being slightly over the full Mark how I always feel them. None of my engines are even at the full Mark they're always a 16th or an eighth above the full mark and sometimes a little more, or if they're down close to the ad Mark but still what is considered safe. Then there's also the variable of having fully synthetic oil or semi synthetic oil that could possibly keep the operating temperature lower during or after shut off.
Then there's the one other variable which I tell people is an absolute no no and that's for the people who get done mowing and are going to idle it down for that 30 seconds or whatever but they want to do it at the same time they're riding the mower back to the garage, barn, or shed.
NEVER do this!.
This can Spike the temperature even higher on the engine because it's still working and moving that 800 to 1,000 pounds of machine in person but it has no air flow for the cooling and it's also terrible on the hydrostatic transmissions because their fan is spinning at a third of the speed as it was when you were mowing and getting up to normal operating temperature and now you have almost no air flow compared to what you did have and you're still moving that machine which could be several hundred feet if you're riding it across the yard or field to park it.
This is not a concern if people follow my rule of if it's moving or mowing it needs to be at full speed.
However to find out if you can keep the temperatures cooler from idling it down once you park it or not we would have to do some actual testing.
I think that if we test the temperatures and then even more importantly had a couple of hundred of these 31xxxx engines to test with repeated heat up and cool down cycles, we would find it doesn't make any difference whether you idle it down or not.
My theory on this is that it certainly is from the hot cold cycles but there's not much you can do to that and what we do has little effect on it.
I do think that some of them that like to have to run pop in the muffler or any of them that otherwise backfire etc is not exactly good on the head gasket and helps push it over the edge and maybe keeping the oil full helps prevent this too but overall I think it's a matter of I think it's a matter of the number of uses.
I see these mowers all the time come in with blown head gaskets and only a small handful early on which is probably some manufacturing defect or assembly error. The vast majority of them have between 200 and 250 hours on them but more importantly they have about 9 to 11 years of use.
The average person in my area only plus between 25 and 35 hours a year on their mower and only those higher numbers if they're bagging leaves and mulching etc.
I've seen hundreds that fit this situation but I have seen a smaller percentage with hundreds of more hours with original head gasket.
My theory is that if you start your lawn mower and run it for 1 hour let's say once a week you'll get that 200 hours or so out of it before the head gasket has been wiggled around from the expansion and contraction of the metals etc and not having pressure in the middle where it blows from the lack of the extra head bolt before it starts leaking and needs replaced ...
BUT if you start the same mower and use it 3 to 4 hours every time you start it, you'll get far more hours (if you don't have to disassemble the engine for some other reason lol) before that head gasket creates a problem.
It's not that the design or the situation has a certain number of hours in it but more like a certain number of mows in it.
What saddens me is that Briggs did nothing to even try to fix the problem. The head gasket they sell you is exactly the same as the one that just failed before it. They could have simply put a metal firing around it I believe and would have helped the problem a lot..
Now for several years we've had aftermarket head gaskets that we didn't have for a long time. Much cheaper too because if you've been buying a lot of these you'll remember that the retail price of the lawn mower shop was about $6.48 just six or seven years ago and then one year out of the blue they shot up to 19.50 to $20.49.
I assume just because Briggs wanted to recoup some of that money they were losing because of all the predator, Loncin and other Chinese engines being purchased instead of their engines.
Then after 2 or 3 years of that the aftermarket was popped up on eBay and Amazon and now the price for Briggs has dropped down substantially at least it had until this new inflation and economy. I haven't priced them in the last year or so because I bought a lifetime supply of them at 6 bucks a while back.
I haven't actually used the aftermarket but from the pictures I've seen it doesn't look like it's much better if any. We know that usually aftermarket isn't as good but in this case it couldn't be much worse than the Briggs one.
Kohler on the other hand had a problem up until around 2003 with their command twins blowing head gaskets and they fixed the problem beautifully.
Not only did they issue a brand new head gasket which was actually a kit that came with head bolts or studs and other associated gaskets to take the intake and exhaust off and stuff like that to do the job but they also recalled every one of the original gaskets from their dealers so none of those old ones that weren't improved would be sold.
This fixed the problem 100% and I don't think I've ever seen a Kohler fail after having this new improved gasket put on.
It's thicker, has a fire ring if I remember correctly, is beefier all the way around with more complete coverage and more contact and surface area.
The only negative to the entire situation was you had to buy the kit and not just the gasket and that kit was almost 50 bucks per side whereas Briggs & Stratton was happy to spit you out another junk gasket for under $7.
Oh well, for those of us who know how to do it it's not even a 45 minute job. I can do them with my eyes closed.
Unfortunately, for the average consumer it's a deal breaker as is any engine or transmission issue with the mower.
At the average lawn mower shop in this country it's between 300 and $400 to get the head gasket replaced on one of these total price so it's not very cost-effective to do unless the mowers fairly new or in very excellent shape.
Even then you could get on marketplace or Craigslist and buy you a similar even newer mower for $450 to $600 that you can cut your grass with the day you buy it and then sell your mower which still starts and runs but uses some oil and maybe smoke some and needs a head gasket for at least 150 to 200 if it's in that good of shape.