TL;DR : Coolant leak somewhere. Hoses seem okay. Thermostat housing and water pump are my suspicions. Pressure test to be done soon. Advice would be appreciated.

For a few months now my truck has been slowly losing coolant. The reservoir never drained large amounts at a time and I could only smell burning antifreeze about one day out of a few weeks.
It had stopped for most of December but around Thursday last week I could smell the burning again. I checked the reservoir and it was nearly empty, it had all drained out when I checked again a few minutes later. I spent 4+ hours with a flashlight in the dark and never found the leak.

Next morning, refilled the reservoir with 50/50 Prestone and waited for it to leak again. Sure enough, reservoir level has already dropped.
A look from the top of the engine bay and I see nothing except some slow ooze from the t-stat housing, but surely not enough to contribute to such a large buildup.
Looking from under, I can see coolant buildup on the passenger tie rod boot, lower control arm, and what I was told is the oil pan? There also appears to be coolant leaking from the water pump, but it may be coming from behind the pump.
I've read on this forum where 3.0's have timing cover leaks common, is it fair to assume this on my 4.0?

That's all I've had time to check for now. I'll be picking up a pressure tester and try to get some pictures soon. If anybody has any knowledge I would really appreciate it! Ask any questions and I'll answer to the best of my ability.

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2001 Ext.Cab Ford Ranger 4.0 2WD 72K

I would curious if you tried using dye. I believe the manifolds are wet and have two freeze plugs each.

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1994 XLT 2 Ext Cab V6 4.0 Vin 'x'

Dye is on my list of to-do's before I have a local shop give me a second opinion.

I got my hands on a pressure tester today. Pumped her up to 16ish PSI, it wouldn't hold pressure and it created a puddle on the passenger side, just about under the oil pan, within a couple minutes.

I'm gonna pull the intake, rad fan, and shroud and re-do the pressure test all this weekend so I can see a bit more in the front.

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2001 Ext.Cab Ford Ranger 4.0 2WD 72K

Check the thermostat housing the plastic ones are known to leak.

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2000 Ranger Extd Cab XLT, 4X4 Off Road, 4.0L, Auto, 8.8 - 4.10's, 01 grille & lights swap.
69 Mustang, modified 5.0, & 5spd.(project)
99 Explorer Sport, 4.0 SOHC, Auto, 8.8 - 4.10's, PW, PL, PM, Cruise, Tilt. (Wife's DD)
05 F-150 2WD Regular Cab. ( My DD)

I had a similar leak in my sport Trac. It was leaking from the seal between the thermostat housing and the block and then running back between the heads. There was a foam insulator taking up the free space between the intake manifold and engine valley that absorbed a bunch of it, so it wasn’t really obvious until it got really bad. Apparently it was a slow leak that went on long enough that it started to eat up the wire insulation on the injector harness so I had some repairs to do there. If you end up finding you were leaking coolant on the wiring, it’s a good idea to check the state of the insulation on the wires.

Heater control valve is notorious for leaking.

My plastic POS t-stat housing was leaking and I think it has been slowly leaking for years. It recently got worse where my reservoir was empty as well. I replaced the housing and while I was at it I replaced all hoses. So far no leaks. If there is crusty stuff on that plastic t-stat housing junk it might be worth it to replace it and see if that fixes your issue. It’s kind of a pain to get to and you have to be careful to not break off the three plastic tabs that guide it to the opening in the block.

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2011 Ford Ranger Sport 4.0 SOHC 4x2