Hi I’d like to thank you in advance for taking the time to help me with this. I have a ZD326 zero turn that is my baby. It has just over 640hr it’s a 2011 and it gets a full service and cleaning after every use. So lack of maintenance is not an issue. I had an overheating issue about a year ago so I replaced the radiator with a good flush of the system. It’s been working great tell a couple of weeks ago when it sounded the overheating alarm and I pulled under a tree. I shut it off as the radiator blew up. Split the top open. As soon as the alarm went off I looked at the gage it was just about in the red maybe an 1/8 from it. Now the radiator was not clogged. The thermostat has been out of it for a while. I’m in fl no need for one here. I replaced the radiator with a new one. New cap with the recommended coolant. Ran the mower for about 10 minutes to check for any pressure buildup. Found nothing to suggest a head gasket. Started mowing and around the 10 minute mark I looked at the gage it was just about to the red and before I could park it the alarm sounded and the radiator split the top wide open again. I’m at a loss need help finding the problem and a fix.
Keep blowing up radiators
- Thread starter Shane37
- Start date
First thing I'd do is stop running it until you figure out why it's making that kind of pressure. A hot engine alone usually will not split two radiators that fast. You need to test for combustion gases in the coolant with a block tester kit; a leaking head gasket or cracked head will pump pressure in long before it actually hits the red. Also make sure you have the correct pressure cap, not a higher PSI one.
Next, with the engine cold, cap off, start it and watch for a violent surge in the neck when you crack the throttle. Gentle circulation is normal, big bursts point to cylinder pressure. Also confirm the fan is pulling air through the radiator and the belt is tight. Did it ever overheat badly before that first radiator?
Next, with the engine cold, cap off, start it and watch for a violent surge in the neck when you crack the throttle. Gentle circulation is normal, big bursts point to cylinder pressure. Also confirm the fan is pulling air through the radiator and the belt is tight. Did it ever overheat badly before that first radiator?
Yes you’re right I needed to look at the time more. But it was in the middle of the gage about 5 minutes into it so I let myself get lost in mowing the outer edge around the fence and before I knew it it was overheated. That’s my fault on that for sure. The water pump I think is working. It was moving the water good when I was letting it run the first time checking everything after the radiator changed.
Hot fluid should blow out the overflow of the cap, sudden excessive pressure tells me you have a head gasket or a cracked head issue. You can get 'combustion test strips' from an auto parts store to verify combustion gases are present.
What about the radiator cap? It should've released the excessive pressure before the rad blew.
Not if the volume and pressure is suddenly more than the cap can vent. An engine simply over heating slowly rises in pressure and once exceeding the cap design, starts to bleed off. A sudden sharp increase may well of exceeded the caps ability. Imagine a full cylinders pressure suddenly being dumped into the coolant.
With a full compression pressure into the cooling system I'd expect to have a hose blow before the radiator.
The OP said he'd parked the tractor before the rad blew. If that was the case what would cause the problem? I dunno.
First - I'm not a mechanic or an engineer
Can the lack of a thermostat be causing the overheating? Doesn't the coolant need some dwell time in the radiator to have some heat extracted?
Is the engine heating and boiling the coolant to the point it flashes to steam? If that happens the steam created instantly occupies 1700X the volume that the water did. No cap that would be capable of venting that.
Can the lack of a thermostat be causing the overheating? Doesn't the coolant need some dwell time in the radiator to have some heat extracted?
Is the engine heating and boiling the coolant to the point it flashes to steam? If that happens the steam created instantly occupies 1700X the volume that the water did. No cap that would be capable of venting that.
The answer is no.
With some subtle caveates the RATE of heat exchange is the same with or without a thermostat. Without the thermostat an engine runs colder because the coolant circulates faster. Thats more volume per unit time which means it absorbes and exchanges more heat per unit time.
The "dwell time" idea is bogus physics.
Dan
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Removing the thermostat may not be a good idea. Depending on the design the thermostat opens the radiator loop and simultaneously closes the small loop, which only circulates the water without cooling (not to dead head the pump). By removing the thermostat you will have an undefined flow, mainly through the small loop, significanly reducing cooling capabilities of your system.
Also the thermostat regulates your engine temperature. Removing it has your engine running at an uncontrolled and unknown temperature.
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Hokie and Hugo are correct. There is also the possibility that removing the thermostat removes so much resistance to flow that the pump cavitates. In any case, I'd test it and reinstall.
I don't know how this ZD is laid out, but there are more cars where there is an air pocket in the heads that won't fill normally. I had an '89 Cherokee 4.0 that had to go through several heat-cool cycles to work it out (I didn't know about the vacuum pump method). So I'd let it cool off and check coolant frequently after draining it.
The other possibility is water pump failure. It's not unheard of for the impeller to come loose and spin on the shaft.
I don't know how this ZD is laid out, but there are more cars where there is an air pocket in the heads that won't fill normally. I had an '89 Cherokee 4.0 that had to go through several heat-cool cycles to work it out (I didn't know about the vacuum pump method). So I'd let it cool off and check coolant frequently after draining it.
The other possibility is water pump failure. It's not unheard of for the impeller to come loose and spin on the shaft.
Heres anorher interesting one. Some early stock car racers removed thermostats to reduce parasitic load and increase cooling. Oddly some wound up with overheating failures. Without the restriction of the thermostat the high RPM operation increased flow force so much it pushed coolant past the pressure cap on the radiator. The engine would pump itself "dry" and overheat.
Thers a lot going on in a modern cooling system and removing the thermostst is a bad idea.
Dan
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You might say they were the first generation of NASCAR restrictor plates
