Still no joy :nenau
Right, here's a breakdown of everything that's been done . . .
Start of Summer-noticed the heater had stopped blowing hot. Wasn't worried as I put it down to a HVAC door cable problem
No coolant leaks. No overheating issues
Couple of weeks ago I started to investigate and discovered that the HVAC door cable was just fine. Still no leaks, no overheating, no other problems with the truck.
Drained coolant from thermostat housing, and replaced it. This seemed to sort out the heater issue until I checked my antifreeze concentration and discovered it was too weak. I then drained the radiator by removing the thermostat housing again and refilled with antifreeze. It's only since then I've been unable to get the heater to work.
I've been working on the (mistaken) assumption that the radiator fills from the bottom (I know, I know, it was just a brain fart
) but it's puzzled me that the inlet hose to the heater has been getting hot, but the outlet hose (to the thermostat) has been warm to the touch, and also that the thermostat opens only when the fan is physically restrained. I've since realised that this is leading to the thermostat opening under ambient
air temperature as it's in such close proximity to the cylinder block. So the cooling fan issue has proven to be a red herring, and the thermostat isn't getting hot coolant to it from the heater outlet pipe.
What I'm now left with is an engine that doesn't overheat whether at idle or under load, a thermostat that doesn't open under the influence of hot coolant (it only opens if I physically stop the fan turning, even after a 6 mile run), a heater that still only blows warm (at best) air when the engine is revving high, and top and bottom hoses both rock hard but only the top hose is hot.
The water pump is obviously fine as I'm getting no overheating and I can see a vortex when the radiator cap is off. Hard revving with the front of the truck up on ramps leads to air bubbles (obviously coming from the top hose, rather than the bottom as my over-stretched brain had assumed) and an increase in air temperature from the vents.
I now also know the thermostat doesn't need to open to provide hot air, as the pump will circulate coolant through the cylinder block, EGR and oil cooler and turbo (I know, I know, it's only now becoming obvious to me as I was making a load of mistaken assumptions)
So, the only conclusion I can draw is that I still have a shedload of air in the system that for some reason won't bleed. I've tried burping the system by squeezing both top and bottom hoses, and studying the schematic from the workshop download isn't giving me any fresh ideas.
Any advice as to how I can sort this is welcome, as I've now scratched a big bald spot on top of my napper. I'm going to add radiator flush, then drain the engine from the cylinder block drain plug (as the workshop download instructs) and refill the system this weekend in the hope that this is will sort it out once and for all :sly
