Anything else to do when changing a head gasket?

[MinnesotaEric]

Best practices on overheating is to Remove and replace the thermostat, get out a machinist's straight edge and check the head for warpage with a feeler gauge (check the block as well).

If you don't know why the engine overheated stuff in the radiator, fan inop, T-stat getting stuck instead of opening all the way (look for little scratches in the brass-if any, you likely found the problem), then pull off and inspect the water pump and check radiator flow (a radiator shop can do this). Consider installing a higher capacity radiator while you're there.

The hearsay I've heard from Bobcat guys is that Kubota heads screw up once they have been overheated and the head needs to be rebuilt every 3,000 hours. If you're nowhere near that many hours, and the head is straight, and your machine shop pressure checked it and found no issues, then slap the head back on with a new gasket set.

Do go above and beyond to try and identify the reason the engine overheated, whether a bad temp switch, or whatever.

 

[Lobanz]

Were you, the OP doing something wrong is difficult to say, but if I had to guess I'd say not too likely. I would ask what you are using any of the machines to do that is creating high load conditions for long periods; and suggest that you might consider hogging more frequently, when the grass is less tall and/or cutting when it's cooler out, late afternoon/evening or earlier morning- if possible, and take some breaks to let the equipment cool down...

Usually, the tractor is used in small spurts, but when it overheated last I was mowing very thick grass and dead crimson clover I planted last fall -- bout an acre. Could only take about a 2' bite at a time. Pretty dense.

An overflow tank might actually help because it could allow pressure and very hot coolant to be able to be released to the tank rather than the current situation where you experience overheating. You could also add, if there is room, a thermostatically controlled auxiliary fan to cool the radiator.

I've been thinking along those lines too. I wedged an aluminum can in the frame and ran the tube in there, but it doesn't seem to help much. Not much room for an aux electric fan on mower and not sure that the tiny little alternator/dynamo could run it and still charge the battery. Many of those take 6 amps or more.

Make sure your coolant mix is correct viscosity, and don't run just water; coolant includes chemicals to prevent water pump destruction from minerals in the water. Try not to overfill the radiator either, especially since you don't currently have a overflow tank.

We use distilled water and antifreeze in both machines. Probably runs kinda weak in the summer though.

You might have a failing water pump on any of the motors you describe, considering the age of each, # of hours used in high heat conditions, and the tendency of water pumps impellers, (fins)to be destroyed be harsh hard water minerals, assuming you have hard water.... Something to consider since the most frequent thing I hear about your equipment is overheat conditions and radiator bubbles....

Yeah. I want to inspect the water pump impellers.

BTW, where are you located that you are experiencing so many heat related issues? And have these issues started happening on your machines just recently?

I live in North Alabama. Hot days do seem to exacerbate the problems. Mower has been happening for a while. Tractor usually doesn't overheat except when run under heavy load for extended periods.

What has you looking for bubbles in your radiators- are your temp gauge needles redlining?

I looked for bubbles because I'm trying to troubleshoot overheating problems! One possible cause of overheating is a blown head gasket. No, we don't run them until the temp gauge goes into the red. We stop and let them cool off if it looks like they might go into the red if we keep on going. Coolant is sometimes boiling by that time though.

 

[rsallen]

Rad fins or the sometimes installed fine mesh protection screen becoming clogged from the fine particles and garbage always thrown into the air when mowing?

 

[Coyote machine]

Usually, the tractor is used in small spurts, but when it overheated last I was mowing very thick grass and dead crimson clover I planted last fall -- bout an acre. Could only take about a 2' bite at a time. Pretty dense.

You're definitely taxing your cooling system under those circumstances.

I've been thinking along those lines too. I wedged an aluminum can in the frame and ran the tube in there, but it doesn't seem to help much. Not much room for an aux electric fan on mower and not sure that the tiny little alternator/dynamo could run it and still charge the battery. Many of those take 6 amps or more.




We use distilled water and antifreeze in both machines. Probably runs kinda weak in the summer though.

Might be weaker than specked but distilled is good use.




Yeah. I want to inspect the water pump impellers.

Definitely do so...




I live in North Alabama. Hot days do seem to exacerbate the problems. Mower has been happening for a while. Tractor usually doesn't overheat except when run under heavy load for extended periods.

Last sentence tells the story as to why; maybe consider lesser times and lower 'loads'.




I looked for bubbles because I'm trying to troubleshoot overheating problems! One possible cause of overheating is a blown head gasket. No, we don't run them until the temp gauge goes into the red. We stop and let them cool off if it looks like they might go into the red if we keep on going. Coolant is sometimes boiling by that time though.

I get that you're looking for causes of your overheating. So your method is to remove the pressurized radiator cap when the radiator is hot enough to boil the coolant? That's a good way to get badly scalded/burned.
I suggest you test your thermostats in boiling water to see at what temp they open/close.

 

[rswyan]

What's exactly what they/you did? Sink the valves or grind the stems down? :confused2:

At the time I pulled the cylinder head (aluminum) to replace the head gasket, the engine had about 380,000 miles on it (probably on the order of 7500 hours, if not closer to 10K)

The evidence of the problem was oil in the cooling system (but no coolant in the engine oil)

Figured, considering the miles/hours, that I'd have do them do a valve job on the head, after pressure-testing it for cracks. They tore it down, cleaned it up and inspected it and the pressure test came back good so ... they resurfaced the faces of the valves and seats, checked the guides for wear (all good) and then trimmed the top of valve stems to compensate for the material removed when refacing the valves and valves seats.

The head was actually within tolerance as far as warpage goes IIRC ... but the original head gasket - being steel-sandwich type affair - had left slight impressions/indentations in the mating surface of the cylinder head. The shop, having worked on this particular type of engine (OM647) before, recommended resurfacing the head's mating surface to ensure a good seal. According to Mercedes that's a no-no and can't be done (it's an interference motor) ... but after measuring the height of head and considering the fact that the valves were riding higher in the head (from machining the valve faces and seats), we decided there was enough meat there to clean it up a little and have it still be in spec.

So they stuck it in their mill - which used a fly-cutter head - paying a lot of attention to getting it mounted correctly, and shaved off a couple of thousandths (0.002 - 0.003) ...

Pretty much cleaned it up smooth as a baby's butt ... although you could still still see very, very faint traces of where the indentations had been ... couldn't feel them running a finger across them though.

I cleaned up the deck mating surface on the block, using emery or crocus cloth and a jitterbug, and inspected the deck mating surface and all the cylinder walls (all in-frame), checking for obvious signs of cracking, and then put it back together.

I think that was around 60K miles ago (which is at least another 1000 hours of operation)

 

[Lobanz]

I get that you're looking for causes of your overheating. So your method is to remove the pressurized radiator cap when the radiator is hot enough to boil the coolant? That's a good way to get badly scalded/burned.
I suggest you test your thermostats in boiling water to see at what temp they open/close.

I just checked it when it was cold! :thumbsup:

How do you do it?

:rotfl:

 

[MHarryE]

NAPA, Auto Zone and probably others have a leak tester. They are about 90% accurate in determining if you have a leaky head gasket! cracked head or block.

 

[Baby Grand]

Nope. Don't have a compressions tester but HF has one with a glow plug adapter for Kubota. Been thinking about it. You thinking about rings?

Actually, I was thinking water pump.
Much ea$ier repair if that's what's ailing you.

 

[Lobanz]

Actually, I was thinking water pump.
Much ea$ier repair if that's what's ailing you.

Here's what the water pump impeller looks like. HERE is a video of it.



I don't see a problem but I don't know what it's supposed to look like. Didn't see any pictures of the impeller online.

 

[Baby Grand]

Looks okay to me.