Bleeding the coolant system. 3.0l

[quixote]

Air-locked again following my heater 'fix' last week. Ran great for a week after refilling with new coolant (turns out I misjudged how much it needed, so I've just been topping it up as needed) looks as though it's got a bit of an airlock again though as the heater's stopped blowing hot again. D'you think leaving both radiator and expansion caps off, and having the front up on ramps will clear it if I leave it running for a while? It's not overheating at all

 

[harlowmaverick]

Its worth a try!
Just obviously keep an eye on the temp

 

[Banshee]

D'you think leaving both radiator and expansion caps off, and having the front up on ramps will clear it if I leave it running for a while? It's not overheating at all

Yes!!!! :thumb2

 

[quixote]

Turns out I have a more 'interesting' issue . . . . .

Seems as though the thermostat has failed closed. Now, I know this should lead to overheating but it isn't. God knows how :nenau

The top radiator hose is hot, hot, hot. The lower one, including the thermostat housing is barely tepid to the touch, while the feed and return to the heater matrix is too hot to hold.

When I took the thermostat out last week to check it, I ran the truck for a couple of miles and she just never got anywhere near warm. I think I prefer her to run too cool rather than too warm (regardless of what the gauge says) so I think thermostat out for the time being is on the cards until a replacement arrives

 

[quixote]

Right. I'm back to being completely baffled!

Swapped out the thermostat for new (82C) and still getting no coolant through to the bottom of the rad. Matrix pipes are heating up and reaching the thermostat (even took off the alternator to check the flexi at the bottom of the steel matrix output pipe) So it looks as though coolant is getting all the way along to the thermostat and no further :nenau

Might be the new thermostat is goosed? Might be the old one is ok. I'm beat.

Any suggestions welcome 'cos I'm fresh out of ideas :doh

 

[quixote]

Nowt wrong with the old thermostat after testing again. It opens just fine at 82C.

Looks as though the coolant's just not getting to 82C??? Maybe I should put a cooler thermostat in? :nenau

Anyone ever come across this before?

 

[quixote]

Been having a think, and I reckon I'm onto something. Coinciding with the heater losing efficiency, I also lost a couple of mpg. I put it down to the truck needing a service, and/or me being a bit heavy with the old right foot Thinking harder, I've also lost a wee bit of power too. She's lust not quite as lively.

Putting the old grey matter to the test though, I've suddenly realised that the viscous fan coupling has the fan engaged permanently, and I reckon this is providing the extra cooling preventing the thermostat opening. That's kind of borne-out by the fact the truck barely warmed up even during heavy driving with the thermostat removed. I bet it's down to a knackered viscous coupling!

Read the 'symptoms' info' at the bottom of this Wikipedia entry

https://en.wikipedia.org/wiki/Fan_clutch

 

[solarman216]

OK lets get our head round thermostats and coolant flow, first off it is usually a very bad idea to remove the stat altogether, the flow rate round the engine can be so great that it causes cavitation pockets behind obstructions to the flow (head bolt positions etc) this leads to local hot spots (really hot) even though the coolant is cold, very bad for the engine, next the thermostat keeps the engine at the prescribed temperature, the fact that the bottom hose is cold just means that at idling little heat is being produced so the stat is mainly closed to keep the temperature stable, now go out on the road pulling a van up hill things change dramatically and as the bottom hose starts to get hot the air through the rad is now also hot such that the viscous fan cuts in drawing large air flow which cools things down, the thermostat is now of course fully open, so getting back to your heater, if the pipe in and pipe out are both hot with the heater on and the fan on then you are simply not taking any heat from the coolant, so heater controls, flaps, air flow through matrix are where you should be looking, Rick

 

[quixote]

I took the stat out as a check, Rick. I'm convinced I' on the money with the viscous fan coupling failing engaged. Nothing else it can possibly be now, and the symptoms fit perfectly. I'll disengage the fan (not sure how yet) and check my diagnosis over the weekend. If I'm right, the 'stat will open as the coolant heats up to the prescribed 82C and we'll get flow.

I've checked, double-checked, and then checked once more for good measure, and the coolant's getting all the way around the engine until it gets to the thermostat housing . . . .thermostat doesn't open, hence coolant's not getting to temperature. It just all fits now. I hadn't considered overcooling, btu that makes perfect sense as to why the 'stat stays closed, but the truck doesn't overheat

 

[solarman216]

good point but not valid, the fan if stuck on will not stop the truck heating up that is controlled by the stat, end of story, you can tell easily if your fan is stuck on, when you first start take the revs to 3k you should hear the roar of the fan which should stop after a couple of mins if half an hour later you rev the engine and it roars then yes the fan is goosed and you will be waisting some HP but that is the only down side of the fan stuck on it will not have any effect on engine temperature, Rick

 

[quixote]

So that leaves us with the question of why is a tested 'stat not opening at the specified temperature? And why the truck's not overheating? :nenau

The truck gets to temperature as it always has, and stays stable (even when towing a horsebox with a couple of horses in it as I did last week before I realised I had this issue)

This is a strange one, but we have a couple of indisputable facts in that a) the thermostat opens at the specified 82C in test conditions but not on the truck, b) there is no physical blockage in the system and the coolant's getting everywhere it needs to, and c) the truck isn't overheating. Oh! And I'm not sure what (if any) effect this will have, but the air conditioning radiator is off the truck so the airflow over the cooling rad' is uninterrupted . . . .

If I'm right, this is the first time I've ever come across it. The only way to check for sure is to either disengage the coupling (which looks tricky from what I've just seen), or install a lower-rated thermostat after checking coolant temperature at the heater matrix outlet pipe (I have an infra-red temperature probe that will give me a starting point)

It's a weird 'un, for sure

 

[solarman216]

no you have missed the point it is opening at the correct temperature, you are expecting to see some result of this but at idling off load you will not, take it for a heavy blast up the road then pull over and feel the bottom hose, Rick

 

[quixote]

take it for a heavy blast up the road then pull over and feel the bottom hose, Rick

That's exactly what I've been checking for mate :thumb2

Even after a good run the bottom pipe is cold to the touch. There's some convected heat on the 'stat housing, but but not a thing a couple of inches down the hose. And the rad's not seeing any pressure. This is what's leading me to now think of over-cooling

 

[solarman216]

it is very difficult to replicate true on load conditions off load, believe me your system is normal, Rick

 

[quixote]

No, something odd's going on mate. I've had the dash out to check all the heater flaps, cables, etc. I've checked the coolant flow through the block, matrix and rad. I've changed the thermostat (and checked the old one for correct operation before replacing it), and I've run the car on the road for a good distance and checked the lower rad' pipe. This started back at the beginning of summer, and I never even thought to check the pipe temperatures as I was convinced it was a broken cable stay affecting the flap. The truck's shown now signs of misbehavior, apart from the slight loss of power (and I mean slight) and the slight drop in mpg. I've been driving the truck to and from work (35 miles away) and the temperature gauge has been rock solid just where it always has been. Easiest way to check is get a lower-rated thermostat and see what happens, I reckon. It's been a head-scratcher, for sure!

 

[quixote]

Think I may have sussed it! I had a faff about today & then thought about it. The thermostat wasn't opening under ordinary driving conditions, so I physically stopped the fan from spinning and lo & behold the bottom hose got hot! :clap

So, I can safely say there are no blockages. Moving on, I can also say no leaks. However, the return hose from the heater matrix is still a good deal cooler than the inlet although things are improving. I think the combination of over-cooling by the fan, and the mother of all air-locks may be the source of my woes. What d'you reckon?

 

[solarman216]

Think I may have sussed it! I had a faff about today & then thought about it. The thermostat wasn't opening under ordinary driving conditions, so I physically stopped the fan from spinning and lo & behold the bottom hose got hot! :clap

So, I can safely say there are no blockages. Moving on, I can also say no leaks. However, the return hose from the heater matrix is still a good deal cooler than the inlet although things are improving. I think the combination of over-cooling by the fan, and the mother of all air-locks may be the source of my woes. What d'you reckon?

Not a lot, the fan cannot over cool it is all handled buy the stat, the fact that your return from the heater is "a good deal cooler" but you say you are not getting heat, so this points to the valve not opening or other restriction, Rick

 

[quixote]

Well, I'm baffled. The 'stat wouldn't open until I shut off the fan. 5 minutes later it was open & the coolant was flowing into the bottom of the rad'. What puzzles me though, is why the matrix isn't getting as hot as it should do. The heat from the vents improves if the engine's revved though . . . . .I'm on the verge of putting it in the garage and letting them sort it out. It's kicking my ass :nenau

 

[solarman216]

Well, I'm baffled. The 'stat wouldn't open until I shut off the fan. 5 minutes later it was open & the coolant was flowing into the bottom of the rad'. What puzzles me though, is why the matrix isn't getting as hot as it should do. The heat from the vents improves if the engine's revved though . . . . .I'm on the verge of putting it in the garage and letting them sort it out. It's kicking my ass :nenau

but the stat is opening correctly, your bottom hose will only get hot under hard driving conditions and you cannot have your hand on it then, your problem is either air lock in heater matrix or the valve is not opening correctly, or possibly a collapsed heater hose, the fact it gets better when revving is because the pump works better at speed so forcing more water through, Rick

 

[quixote]

your problem is either air lock in heater matrix or the valve is not opening correctly

'Valve'? I've been reading about some systems with a flow-control valve in the matrix inlet circuit. . . . .I was having a look for one but couldn't see it. Is this what you mean?