How to diagnose any possible engine damage from overheating

Pressure test the cooling system after repairing the radiator. This will tell you if you've blown a head gasket. Now to see if you've damaged any rings etc. you're just going to have to drive it and see if oil consumption remains reasonable.

nate

Year please? 4 or 6 cyl?

Is the "check engine" light on? If it is, and if the code that was set is for "engine coolant temperature out of normal range," a GOOD scan tool can pull a "freeze-frame" and tell you what the temperature reading was at the time the code was set.

A five gas analyzer can be used to test for the presence of hydrocarbons or carbon monxide in the cooling system which may catch a head gasket problem not otherwise apparent yet.

The Honda 4 cyl engine is pretty rugged. All aluminum is actually MORE rugged construction than cast iron block/aluminum head construction.

Don

It is a 05 Odyssey EX. It is a V6.

Thanks Bob

A compression (or better yet, cylinder leak-down) test will tell if the rings have lost their tension. A cooling system pressure test will tell if the block and/or head has warped allowing the head gasket to leak.

If it passes those, it should be OK.

Actually Nate is right, drive it and see.... Having delt with a car that had been overheated, I did a compression test and everything was fine. Some miles later it had hellish blowby... The rings had given up after I did the compression test and repaired the problems.

Yes, this is due to glazing of modern oil additives on the rings under extreme heat conditions. Briggs and Stratton has done studies that document this phenomenon. They recommend against using any modern automotive oils in their small air-cooled engines for this reason. Under the right conditions (hot summer day, dust and lawn debris on cooling fins or restricting airflow, etc.) using modern automotive oil versus the recommended straight weight oil can make the difference of a lawn mower's rings lasting 10 minutes or 10 years. Changing the oil right away after an overheating incident is a good idea.

-jim

Since it's an automatic, with water cooling, maybe see / smell if the tranny fluid is burnt. Probably not, but it's a cheap check

Now you talk about "myth and legends..." oils and small air-cooled engines are ripe territory for that. "Never use a multi-grade oil in a lawnmower- it'll coke and glaze and cause failure!" (probably true in the early days of multi-grade oils, actually, but many oils made specifically for small air-cooled engines these days are multi-grade). "Never run ANY automotive oil" was another myth, as was "never run a detergent oil in an air-cooled engine." Completely bogus. The main thing is to run the right GRADE, and far too many people think an air-cooled engine needs uber-thick oil. Briggs (and many other) small engines are splash lubricated, and too thick an oil simply won't lubricate them fully until they're very hot. Most small engines recommend SAE 30 or SAE

10W30 oil, not 50-weight. They're lawnmowers, not radial airplane engines!

Here's a typical Briggs & Stratton Oil Recommendation that comes with the small engines they sell I quote:

"Air cooled engines run hotter than automotive engines. Use of multi-viscosity oils (10W-30, etc.) above 40=B0 F (4=B0 C) will result in=

high oil consumption and possible engine damage. Check oil level more frequently if using these types of oils."

Of course they put this in fine print so they can sell a new lawnmower engine to the ignorant every couple of years. Their recommendation for the best oil for some of their hottest running little engines is to use straight weight API type SC which is I believe what cars used back in the 50's and pretty much has no additives. They have different recommendations for different engines but the main issue is temperature. Snow blowers can use modern automotive oils (10w30 5w30) without problems. They don't say never use multi-grade oils. It's only when temperatures are above 40=B0F that they recommend against. It becomes a much bigger issue when the temps are in the 90's and the engine has accumulated dust and lawn debris in the cooling fins. Under those conditions putting the same oil as is in your car is almost guaranteed to fry the rings.

If you want to claim they are lying go ahead, but it is not a myth that they have studied this extensively and they do make these recommendations.

-jim

Do they say anything about synthetics? I bought a new Briggs mower a couple of years ago, and changed to synthetic after the engine was fully run in. (I bought it from my sister, who found she couldnt handle it..She had lost the warantee receipt and other documentation)

Soon after I shifted to Mobil 1, it started using oil disastrously. When I talked to the garden shop representative at Lowes, he said that Briggs had warned against using synthetics just for this reason. He suggested that if I rebuilt the engine using high quality chrome rings, it might hold.

I honed the cylinder, and rebuilt it using standard Briggs and Statton parts, and it worked okay for a short while. Then went back to burning oil like crazy. Gave that POS away. In the future, I will be a bit more careful with warranty documents AND with oil changes.

You need to read the documentation that comes with your particular engine. They do recommend synthetics, multi-grade, high detergent or whatever in some of their engines. The issue is temperature and their engines are not all built with the same design. For a push mower with a small engine how deep the grass you are cutting can be a significant factor in how hot the cylinder walls get. As you load down the engine you create more heat and less capacity to cool the engine - so it obviously gets hotter. With modern automotive oils at some point where the engine reaches a certain threshold temperature the rings seem to go downhill pretty rapidly. I would think that temperature threshold point would be higher for synthetics, but if they recommend against synthetics in some particular engine than it is probably not high enough for the worst case (hottest) scenario.

So you buy a new lawnmower and when it's new its got the right oil in it. So a year or 3 later you decide to change the oil one spring. And you put the same stuff you put in your car in the lawnmower. And you mow the lawn for a couple of months and everything seems to be fine. Then along comes that brutally hot spell in August and you think you'll wait till it cools off to mow the lawn, but it doesn't cool off and so you get out there and mow your knee high grass. The next thing you know your lawnmower is an oil burner - which is good because the mosquito's were starting to get really bad :^)

When you read that someone has an auto engine that overheats and immediately after the incident it has good compression, but that it rapidly degenerates into poor compression soon after driving it for a while you have to suspect that the same phenomenon is at work there.

-jim

That was my first mistake..no documentation

You did not understand my post. I ran the original oil until the engine had a chance to break in...Estimate 5-10 hours... Not an old engine at all.

After rebuild, the engine probably ran another 5-10 hours before it lapsed into fumigation mode.

The engine did not last one season.

Most synthetic oils have very good flow characteristics. This is a good thing in a circulated oil system, but it is a major problem with engines that use splash-plate lubrication. The oil runs off the plate before it has a chance to splash it up anywhere, and the end result is poor lubrication.

There ARE synthetic oils designed for small engines, which are a bit more sticky. They have the adhesion of a petroleum oil, while having the high breakdown temperature of a synthetic. Royal Purple makes one that seems to be good; we use it in generators where the engines may sit for several years without more than an occasional ten-minute test run.

--scott

No actually you misunderstood my meaning. I didn't mean that is what you in particular did. I meant that is what people in general do. You probably would have gotten atleast 5 years out of it if you hadn't changed oil at all.

My push mower is about 10 years old and doesn't burn any oil. I have never had to add any and have changed the oil maybe 3 times.

-jim

My understanding is that this was a problem with EARLY synthetics, but was corrected years and years ago. Early synthetics exhibited the same problem in pressure-lubricated engines, but in a different way. The oil would drain out of vertical bearing gaps (namely the crankshaft thrust bearings) and there would be insufficient lubrication on cold starts, resulting in high thrust bearing wear. Modern synthetics don't have this problem.

If it was a 3.5-horse or less Briggs, that's not surprising. While those

*used* to be very good engines back in the 50s and 60s, they've been complete crap since the 80s. The 5-horse and larger engines are still quite good- far better than the imports IMO. But if you need a 3-horse class mower, get one with a Honda or Tecumseh engine.

Not if its a synthetic oil. I've been running synthetic 10W30 in a 1994 Briggs 6-horse lawnmower engine since it was new, changing the oil once per year. It doesn't use ANY oil between changes. And I don't exactly live in a cold climate (Austin TX) and mowing season runs from late February through November (into December counting leaf-mulching season) so that little engine's got a LOT of hours on it.

The engines aren't any worse in fact there made better its the oil you put in them that is not holding up. If you put the same type oil you put in them in the 50's and 60's they last longer than they used to.

Briggs says synthetics are OK for most of these engines - RTFM.

-jim

Well, that is exactly the engine in question. It had a noticeable ring ridge after the few hours it ran. I removed the ridge, and felt that the aluminum seemed to be awfully soft. In fact, I had some misgivings about honing it at all, but did anyway...Tried to give it a reasonable finish.