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I have a ZD28 and I'm not getting voltage to my glow plugs. I was having rough starts in cool weather but fires up great when warm. The glow plug lamp lights up so I want to try to troubleshoot the relay before going after the controller. Does anyone know where the glow plug relay is on a ZD28?

Sorry for the late update, but the root cause was a cracked cylinder head. It was not a cheap service call but I found a good mechanic and shopped around for new OEM parts and she's back in business...no more burning coolant, white smoke, or irregular temps are start-up. The prior owner had...

I think I figured out the root cause of the temperature spikes... When starting up the tractor the other day I noticed the radiator overflow tank was bubbling, but it was cool to the touch so it wasn't boiling. When the thermostat opened and coolant circulated the bubbling stopped. Looks like...

I ran the temperature trace this weekend and also monitored the sensor voltage to the instrument gauge. It shows the red line spikes are start-up and stablized after about 8 minutes. My white smoke is pretty brief now, I'm guessing my oil and filter change may have helped. Here's the link...

Will do. This weekend I'll take a thermal trace from start-up to stabilization so I'll have a nice graph to look at instead of trying to scribble down temperatures and times. I'm thinking I'll record: exposed part of the thermal sensor, water pump, top and bottom water pipes, and then maybe a...

I haven't tried that yet, but I can. Occasionally a couple drips will come out of the reserve tank tube (open to the ground), but no overflow at the radiator cap. Thanks again for all the suggestions...if I can't figure this one out I'll eventually have it picked up by the dealer.

And yes, the 95C is from stone cold, which yesterday wasn't so cold at 85F (or 29C).

It was a thermocouple taped to the exposed portion of the thermal sensor, connected to a handheld fluke 51 (as an Engineer I have access to some nice loaner equipment). I used an IR thermometer to measure the temperature at the water pump. When the needle stabilized in the middle of the gauge...

I replaced the temperature sensor last night in addition to changing the engine oil, filter, and oil pressure sensor (it was corroded and housing was chipped). When changing the temperature sensor at the rear of the block it gushed coolant so I'm pretty confident there's no blockage issues...

Valid point. I'll troubleshoot the sensor tonight with a boiling pot of water and gradually cool it (or vice versa) while monitoring the temperature gauge.

The temp spikes occur probably within 30-60s of starting (they're not immediate). I'll test the temperature sensor separately tonight.

That certainly makes sense, I may try that once I verify the sensors are all OK. One other thought - I've flushed my coolant system, but maybe I have some debris in the engine block that is preventing me from getting coolant deep inside? That could explain the temperature spikes at start-up...

There is no over temperature light, just battery, oil pressure, and glow plugs. I unplugged the thermo-sensor switch and tied the wire to chassis ground and a loud horn went off - scared the crap out of me. I guess that explains what that switch does!

Update: After installing the new thermostat and gasket, and refilling the radiator, the temperature still spikes at start-up and stays near the red line for a few seconds before dipping down and repeating several times. Before throwing in the towel and calling the dealer, my next thought is to...

By the way, can anyone suggest a good online source for parts? Messicks.com?

Thank you, very good advice. I'll go ahead and get some of that paste in addition to the new gasket. I put both the old and new thermostats in a pot of water last night and gradually increased the temperature. The new, genuine Kubota thermostat opened sooner (at about 80C), quicker, and...

Great idea about about cooking the new thermostat first. I'll go ahead and do that. I got the new thermostat and gasket from the dealer this weekend but when I got home I noticed they stapled the two bags together and sent a staple right through the gasket...let's hope they have another one...

Thanks for the input Stubbyie. By the overdamped control loop, I'm referring to the operation of the thermostat not the resistive sensor that's moving the needle in my instrument cluster. Once the new thermostat comes in I'll replace the old one. Just for the heck of it I was thinking of...

I was also thinking electrical problem. I will trace the wiring to double check, but since the needle is stable after warming up I think it would maybe be a late opening thermostat which would explain the quick temp drop (as coolant runs past the sensor). My temp oscillations are only at...

Yes - I will be picking up a new thermostat and gasket immediately. I'm curious though...is it normal for the temperature to oscillate then settle down? I certainly don't see anything like that happening on other engines, but I'm not very familiar with diesel operation yet.