Thermostat stuck...Overheated engine w/damage

[ZD28 Dean]

Hi, and apologize in advance for the long-winded post.
I have a ZD28 mower with the 3 cylinder D1105 engine. It overheated and I didn't catch it until it was WAY HOT (pegged the temp gauge, and I later determined it turned out to be a stuck thermostat. ). I made a bee-line for the garden hose. I didn't shut it down immediately, I brought it to idle and attempted to refill the radiator. It didn't take water, so I attempted get circulation again by removing the thermostat housing. It then took water and the temp gauge went to cold. I shut the engine down about a minute later. Total time from when I noticed it was hot till I got the temp gauge reading cold was about 6-7 minutes, the engine idling all the time.
After pulling the thermostat and resealing the housing I tried to restart the engine to finish mowing. The engine started very hard and once it fired, it spit water out the exhaust. I removed the radiator cap and found bubbles continually venting from the top radiator tank.
I started to tear it down, hoping it was just a bad head gasket. The valve cover had milky white oil residue inside it, but the dipstick from the oil pan did not show any coolant contamination. I didn't find any obvious problems with the head gasket, but I did find a crack in the head from the exhaust valve to about where the pre-chamber port is in the middle cylinder. I am assuming the head is junk. I rolled the engine over and visually inspected the cylinder bores, and didn't see any evidence of damage.
My dilemma is: Do I remove the engine and tear the block down to inspect, or buy another head and a gasket and reassemble? How likely are these engines to crack a block from overheating? I believe I read somewhere that it is exceedingly rare, but that one person recommends new rings since overheating can cause them to lose their temper.
I am hoping an experienced mechanic will chime in with their opinion. And maybe a member who might have a head assembly they are looking to sell for a reasonable, dare I say cheap, price.
Again, thanks in advance for any insight anyone might provide.

 

[Tractordoctor]

Since you have not seen bore damage, if it would be mine I would install a new cylinder head ,gasket ,thermostat and call it good I have did several cylinder head replacement because of overheating and never had a block, ring problem. I don’t have a cylinder head for you sorry. But I have 2 good v1505-4 head that came off a f3990 if you need some good luck

 

[DustyRusty]

When I had my auto repair shop, I had a customer do the same as what you did. After inspection, and assuming no damage to the block, I sent the head out for magnafluxing, and it came back with a clean bill of health. Problem was that the block was cracked in a place where I couldn't visualize, hence once the engine got hot again, the crack opened up and was blowing coolant out of the radiator. If he had done nothing, there is a strong possibility that the engine wouldn't have been damaged at all. I would start looking for another engine because cold water in a hot block does a lot of damage. You could replace the head and head gasket, but you might just be wasting your time and money.

 

[ZD28 Dean]

When I had my auto repair shop, I had a customer do the same as what you did. After inspection, and assuming no damage to the block, I sent the head out for magnafluxing, and it came back with a clean bill of health. Problem was that the block was cracked in a place where I couldn't visualize, hence once the engine got hot again, the crack opened up and was blowing coolant out of the radiator. If he had done nothing, there is a strong possibility that the engine wouldn't have been damaged at all. I would start looking for another engine because cold water in a hot block does a lot of damage. You could replace the head and head gasket, but you might just be wasting your time and money.

That's the worry that is on my mind. The only possible mitigating factor is that the block really didn't take the cooler water very fast because the thermostat was stuck and didn't allow circulation until I loosened the thermostat housing and let the water spuge past. Is there any way to verify the block's condition short of tearing it down completely? Not necessarily to LOCATE a crack, but just to verify that there is or is not one somewhere in the block?
I have uploaded 3 pictures of the head. The first has colored circles indicating the closeup areas of the two other pics. I note that the center cylinder combustion area seems to be more "rusty" than the other two, and that is where the large obvious crack is. I had noticed this season that it took a few more seconds to "clean up" after starting it, which makes me wonder together with the rustier appearance of the center cylinder combustion area if this crack might have been there in a smaller form for a while. I'm not sure if the area circled in yellow is actually a real crack. No where else on the head or head gasket showed any bad signs.
My dilemma is that there is still at least 2 months of mowing season left here in Minnesota and mowing my 5 acres with a friend's borrowed and worn out JD F910 makes a 2 hour job a not fun 3.5 hour job of poorer quality.
I have looked for a reasonably priced used engine for a month now to no avail, and yesterday hoped to win a low auction bid on a BX series compact tractor that fell off a trailer in transport and got pretty bent and broken. Damn thing still went for almost 4k.
I hear your advise, but also have to be mindful that this mower has about 2700 hours on it and is a model known for hydrostat problems. I already did the charge pump/drive motor replacement kit once a few years ago...and I do have one hillside that I have to mow. I have been looking at replacement heads. Ebay is full of heads with valves and springs installed for around 450-500 bucks with a gasket set. I'm assuming these are Chinese knock-offs. I saw a couple used heads for about 400 bucks plus another 50 or so for a head gasket. I'm really inclined to roll the dice with either of these options, especially if I could determine a way to check the integrity of the block while still in chassis. If I did, what's the opinion of the new Chinese knock off vs. the used Kubota OEM head? My usage is 2 hours per mow on my estate acreage. A newer 300 series (6 foot deck is pretty much mandatory) is not really in the cards...at least for another 3-4 years.

 

[DustyRusty]

As a mechanic friend that has an extensive background in engineering and engines, says, once you overheat an engine, you start taking miles or hours away from its longevity. The consequences of overheating an engine might not show up for 20 or 30 thousand miles, and the failure will most likely be blamed on some other consequences since the overheating event isn't even a thought because of the time that has passed.
You can roll the dice on a head and gasket, and you will have the answer within 30 minutes of starting the engine after the parts are installed. If you buy a used engine, it will come with a used head. I suggest that you start calling or visiting Kubota dealers, and see if they have any "scrap" engines lying around that you can buy inexpensively. You might get a good head that way.

 

[1badDart]

The block can be pressure tested, but you’ll need a deck plate to do it.

 

[ZD28 Dean]

The block can be pressure tested, but you’ll need a deck plate to do it.

Thanks 1badDart for the response!
I had a hunch that could be done, I'm a machinist by trade...but not an engine machinist/rebuilder. So, could I literally machine a piece of 3/4" thick aluminum plate with all the head bolt holes, carve 3 through holes in it a bit smaller than the cylinder bores and torque it down? Then block the water pump inlet and pressurize from a plate tapped for an air fitting bolted to the thermostat housing flange? If so, how much pressure is generally used?
Are all the passages in the block interconnected without going thru the head? (does the deck plate need passages in it?) Would I need to use a head gasket, or would RTV silicone sealant be adequate for the pressure test?

 

[1badDart]

Thanks 1badDart for the response!
I had a hunch that could be done, I'm a machinist by trade...but not an engine machinist/rebuilder. So, could I literally machine a piece of 3/4" thick aluminum plate with all the head bolt holes, carve 3 through holes in it a bit smaller than the cylinder bores and torque it down? Then block the water pump inlet and pressurize from a plate tapped for an air fitting bolted to the thermostat housing flange? If so, how much pressure is generally used?
Are all the passages in the block interconnected without going thru the head? (does the deck plate need passages in it?) Would I need to use a head gasket, or would RTV silicone sealant be adequate for the pressure test?

I wouldn’t think you’d need more than one port to pressurize it. 18-20 psi should be plenty. What is the radiator cap rated at?

There are kits that will pressurize the system through a radiator cap with a fitting in it. Check your local Advance Auto Parts and see if they have the kit in their loan a tool program.

Justin

 

[ZD28 Dean]

I wouldn’t think you’d need more than one port to pressurize it. 18-20 psi should be plenty. What is the radiator cap rated at?

There are kits that will pressurize the system through a radiator cap with a fitting in it. Check your local Advance Auto Parts and see if they have the kit in their loan a tool program.

Justin

I believe the cap is 12 psi. I already have the head off of it, and I see a crack in it that I'm pretty sure was the problem. I wanted to test the block independently for some peace of mind if possible before committing to installing a new head and head gasket.
I'm not comfortable pressurizing an aluminum core radiator, too easy to over pressurize and damage it. I'd more likely simply loop the upper and lower radiator hoses with a "T" and introduce an air charge to it at that location. So, around 20 psi and then see if it holds that pressure over half hour or so?
I get that some cracks only open up once things have come to operating temp, but block damage is far less common than head damage from overheating, so if it checks good cold, I"d have sufficient confidence to go ahead and fork out 500 bucks on a head and gasket and see what happens. Every other option starts getting to be a bigger investment than I'm comfortable making on this model and vintage.

Again, Thanks to everyone who responded with their thoughts!

 

[D2Cat]

You local engine rebuild machine shop should be able to magnaflux the head easily and inexpensively.

 

[whitetiger]

note that the center cylinder combustion area seems to be more "rusty" than the other two, and that is where the large obvious crack is.

From the picture, the crack you have circled in blue is definitely your problem and has been cracked, probably to a lesser extent for some time.
Replace the head and you should be OK. I have replaced dozens of cylinder heads on the 3 cylinder engines in ZD's, BX's, and RTV's and I have yet to find one with a cracked block.

 

[Firefight100]

I agree, that head has been cracked for a long time. And that cylinder has had water damage for a long time also. That pitting in number 2 didnt just happen.

 

[Pau7220]

Definitely a large crack... then cold thermal shock after overheating... it started hard...then water shot out of the exhaust. Did you check for obviously bent rods by bringing all 3 pistons up to the top of the deck to make sure they top out equally?

 

[lugbolt]

agreed the head has been broke for a long time. Replace it.

Kubota blocks generally don't crack, almost always just the head as it's the hottest part of the engine.

OEM only. I've put one or two chinese heads on and one of them had a valve seat come out and destroy the engine in it's entirety. As the tech, I was on the hook for it--but the owner knew he took a chance on an aftermarket head and owned up to it. I installed the new engine and it's still running to this day.

definitely check for bent rods. Suggest using a depth micrometer. Certainly wouldn't want to put a head and gasket on it just to find out that the rod(s) are bent, then have to pull it back apart again. 3x the work.

It would have been best to check engine compression before teardown so you know the condition of the pistons/rings. On severely overheated engines it's common for the rings to be stuck in the ring lands of the pistons usually resulting in loss of compression. So at this point since it's already apart and you really can't do a compression test without reassembly, may as well pull the pan, knock the pistons out and re-ring them. Measure the bores with a dial bore gauge to verify concentricity and no or at least VERY little taper.

We have to remember how a diesel engine runs. Compression-ignition. Compression heats the air to a point that the fuel will ignite on contact with the hot air. The larger the engine, the more pressure it can generate, and the smaller the engine the harder it is for it to make enough pressure. With that in mind, these little small engines tolerate VERY little air loss through the rings, gaskets, valves, etc, until it will no longer generate enough pressure (and heat) to ignite the fuel charge. So what they have to do is close the intake valves early, then design the pistons such that the space at the top of the crown is small, and close the gap between the crown of the piston and the bottom of the head as well as keep the prechamber size small. All of which reduces the margin for "errors".

a 14 liter diesel's cylinders are so large that they'll generate that heat even with significant leakage. A 1L engine is much less tolerant of cylinder leakage.

Lots of considerations in these cases. Good luck.

 

[challer61]

Your head is seriously cracked