Changing a thermostat (car)

[Cigaro]

Hi all

I need to change the thermostat on the Polo tommorrow as it's stuck open. I know where it is and how to change it, but the Haynes manual seems to think I need to drain and refill the cooling system while I'm at it.

Is this strictly nessecary as it seems like an awful lot of faffing - mostly because I'll have to find a container to drain all the coolant into! Or can I just top it up afterwards, and do I need to bleed it if so (and how)?

Cheers

Rowan

[T1z3R]

if the stat is high on the engine then i wouldnt bother draining it. if its somewhere low down then youd be better of draining rather than have it all come flooding out when you remove the old one.
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duck my sick!

[Darth]

Generaly when you pull out the thermostat you are gonna be draining the system whether you want to or not. Wouldn't feel the need to specifically try to drain it first though. As said above if it sits high up on the engine you shouldnt lose too much coolant. Be sure to get any airlocks out after its all back together too
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Harold_Shand wrote: I suppose it's like anything, you get your fingers burned when you start out, you learn from it and eventually become a complete arsehole about the whole thing.

[Bikeless]

Just change it when the engine is cold then top up the system and rev the engine with the expansion tank cap off to clear any air locks,you can test the old thermostat by dropping it into a pan of boiling water.

[carvell]

As people have said, it's a closed system, so you're gonna be draining a load of it whether you like it or not
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Yamaha TDM 850

[Phoenix]

Don't know where it is on a Polo, did mine on my Pontiac a few months ago and it was inbetween 2 hoses at the top of the engine so I didn't need to drain any coolant, I also have bleed screws built into the top hoses to make refilling and bleeding easy, may be harder for you At least the Americans make sense sometimes.

[MarJay]

I did it on my beemer a few weeks ago.

Removing the stat would have caused much coolant to go flowing out over the belts and pulleys at the front of the engine. I didn't want that.

I drained the coolant, it took about half an hour, and I replaced the coolant with brand new quality stuff. This was a good thing, as the old coolant looked like urine.

I'm told that when it goes like that it is acidic and attacks the inside of your engine. If I were you I'd just take the minor hit and change the coolant. Your car will thank you in the long run.
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[WildGoose]

It's a daft design to have to drain the coolant to change the thermostat, but that doesn't mean you won't necessarily have to do it.

Depends where it is, of which you haven't said. Common place would be upstream of the radiator top hose in a little plastic housing, but they can put it elsewhere.

If you are changing your coolant make sure you use the same stuff that it had in it, colour isn't necessarily a clear indicator as they come in loads of colours now. The important thing you need to check is whether it is silicate based, or silicate free. The two don't mix well apparently, won't do your engine harm as such, but will cause premature breakdown of the corrosion inhibitors in the antifreeze.

If you have to change to a different sort, its advisable to flush system with a hose or something to clear out the remnants of the old coolant as best you can.

Antifreeze itself, mostly ethylene glycol doesn't wear out ever, but the corrosion inhibitors get used up over time and this is what causes the corrosion in your engine.

Mix the antifreeze 50/50 with deionised/distilled water.

I wouldn't lose too much sleep over it though, as the majority of car drivers haven't a clue and just pour tap water in, so you are fighting a losing battle from the start with a cheap used car.

The haynes will explain the bleeding process for your particular car, some just let the engine run with the expansion tank open and self bleed.

To help yourself along, pour the antifreeze in as slowly as you can, to prevent the "gulp gulp" type effect that will create air bubbles in the system.
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So in other words, he stopped you for being flagrantly in posession of a motorcycle in direct contravention of the Hippies, Darkies and People Whose Face I Don't Like The Look of (Police Powers) Act. 1976

[Cigaro]

Well, I did it yesterday.

Completely flushed the system and changed to pink G30 coolant which is recommended by VW. Everything went to plan, but it took 4 hours as I couldn't get the f*cking bottom hose clamp back on after taking it off! I'd be a shit mechanic

It's in a plastic housing next to the cylinder head. Quite easy to get to in fact, only two bolts (and you have to remove the distributor, but that just clips off).

my car now warms up properly and I have heat again, so thanks everyone

[WildGoose]

[Cigaro]

You're telling me. It would have been OK if I'd had the right tools (a pair of pliers that worked) but I had to do it with molegrips, and it's in the most awkward place ever so you have to sort of lie under the car whilst trying to wiggle it on.

Only slight problem I had was that the new O-ring wouldn't fit, so I re-used the old one, but I checked for leaks and it seems fine. Cheers