Water pump on its way out, or something else?
 

My 2004 Discovery with 145k miles has been showing very erratic water temperatures on the Scangauge, and it's making me nervous. I have Extinct's inline thermostat mod. When I installed it, I didn't get the thermostat perfectly centered, and it shot small amounts of coolant around the front of the engine under heavy load. I noticed this and fixed it, but then a chirp developed at the front of the engine when under heavy throttle. It's not the chirp of a slipping belt, I think. I initially thought this was just a pulley, and so have been putting off dealing with it, but now I'm seeing crazy temperature fluctuations, which makes me wonder if it's the water pump.

​​Here's what I'm seeing. When at idle, about half the time the temperature will climb fast from 183.2 up to 212, 220, 230 in a matter of 30 seconds. I can bring it down by simply revving the engine or driving, and the temperature comes back down very quickly to normal running temperature in about a minute. So the temperature changes very quickly.

My questions are: can the coolant temperature actually change that fast, or is my temperature sensor going bad? If the temp can change that fast, do I need a new water pump? I have no idea if it's been replaced, so it could be the original one.

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Unlikely, too much thermal mass to change that fast. Engine block and heads, intake manifold, oil pan, 5 qts of oil, gallon and an half of coolant, radiator mass, etc. You can check with an IR temperature tool. I keep one of these in the console.

This does not sound like a water pump to me- especially because you can bring the temp down, specifically with revs.

In terms of the temps jumping like that, I have absolutely seen jumps like that within 30 seconds, so it’s entirely possible. This brings me to the immediate issue I think you have and that is air in the system. Even the smallest bit of air can cause this.

Otherwise, as I have done with all my D2s, I end up replacing the entire cooling system (radiator, T stat (and I just stick with soft spring 180F OEM), fan and clutch, and with my Alveston a Flowkooler pump). Water wetter, simple 50/50 coolant. Very thorough bleeding, and I’ve never had temp issues unless a component has failed.

Your chirping could be an idler pulley getting ready to let loose. When I was prepping @Yeti to have his for a fly and drive, the pulley tanked as I was driving to the parts store for something else and I ended up replacing it right there in the parking lot- took 10 minutes.

Thanks for your replies. The first time this happened I figured it must have been a bubble on the temp sensor. I thought, "Huh. That's kind of cool." But then it happened again and again and again. I did have some issues bleeding the coolant system after installing the inline thermostat, so I'll try to get some more air out. There is the occasional gurgle in the heater box in the dash, so bubbles are present somewhere. Maybe they migrated with the cooler weather. If that doesn't solve it, the IR thermometer will be my next step. I have a retired mechanic a couple houses down from me, so maybe he has one I can borrow.

And I'll get on that pulley haha

Might want to go back and read the bleeding portion of the inline thermostat installation instructions

Might want to go back and read the bleeding portion of the inline thermostat installation instructions

If you’ve got gurgling, it’s air. The in line deal should make that a lot easier as well as keep your temps more stable.

Deleting my previous question about having the heat on when bleeding because now I'm 90% sure my water pump is indeed dead.

I attempted to follow the bleeding instructions with very poor results. I started the engine with the coolant cap off and let it come up to temperature. It continued to climb up to 210, and my attempts to rev the engine to bring the temperature down did not work. I heard two loud pops from the heater core, which I hoped were bubbles freeing themselves, but nothing changed. I turned the engine off to avoid overheating and checked on the coolant hoses and thermostat. Everything was cold, indicating that no coolant was flowing through the engine.

Almost impossible for the water pump to not be pumping if the pulley is still attached. If you see any movement in the coolant tank the water pump is working. BTW, you do not let the engine come to temperature to do the bleeding with the inline mod, go back and read the instructions carefully. If the thermostat housing is hot and the upper radiator hose is not the thermostat is not working, remove it completely and test the system. If the top radiator hose is hot but the passenger side of the radiator is not then the radiator is plugged.

When my power steering pump went out I heard a random chirping. I had one of the power steering lines burst while I was driving. Don’t know how miles I drove, I’d say shy of a hundred. It was all interstate and I thought the random chirp might be a u-joint. Pulled off for gas and had no power steering. Didn’t notice at speed. Anyway, the chirping was the pump. Just something to think about.