Coolant and Heating System overhaul 3

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Introduction to removal of water pump or thermostat on 1.9DG Engine

(article penned by CovKid) Thread link:

Firstly, I've written all this to help you do this job without it ending in tears - and believe me it can. Although you can in theory just change the thermostat (see thermostat removal process below) if either pump or thermostat is faulty, its better to do both if the condition of them is unknown. Likewise, if the pump bearings have gone requiring a pump swap, you should change the thermostat too. In general, this job should be approached as an overhaul due to the amount of corrosion you can encounter as well as stuck/seized bolts. In my honest opinion (and you'd do well to trust me on this), it is better to remove it all, clean everything, replace any damaged bolts, and reseal, than leave it and have a major problem on the road at a future date. If you approach this with short cuts in mind, you'll pay for it dearly.

The 1.9 thermostat housing differs from the 2.1 and others post-85 and it can develop pinhole leaks, particularly if antifreeze concentrations have not been maintained. The housing is like gold dust as they rarely come up second-hand and are not available new so you should make every effort to avoid damaging it.

If I had to give this job a grade in terms of difficulty, I'd give it a 10 out of 10 for testing patience and requiring tools most people won't have to hand - be prepared for that! DO NOT underestimate this job. You can be faced with all kinds of problems due to old or stuck bolts. Take your time, don't lose your rag, and THINK before you make your next move. Always imagine worse case scenario and try to mitigate any chances of making a bad situation even worse by damaging something. If you encounter something stubborn, read this article again over a brew and decide how best to proceed. Certainly allow a couple of days (minimum) to do this. It took me a week!

The pump for these engines isn't that expensive compared to others. Watch out for 'cheapie' thermostats - its is NOT unusual for new ones to be faulty. Brickwerks do good ones but in any event, TEST it in boiling water to make sure it actually works as intended, before fitting.

Thanks to Tom Carrington for providing pointers to removing the pump. Even he acknowledges its not fun:

Tools required: Socket set, bolt head remover kit. Everything to be honest, and replacement M8 allen bolts from a decent tool shop, not a store chain which charges the earth.

Diagnosing Pump Wear & and thermostat problems

Noise from bearings - can sound like tappets (or just squeal initially), constant need to adjust fanbelt culminating in sudden loss of water pressure, extreme needle movement on temperature gauge (ie Max) and clouds of steam. When cool, jiggling the water pump pulley (to left of main pulley) and ideally with belt off, will cause a dribbling or gush of water on the ground. The pulley will probably feel loose if the bearings have gone. Other items are likely to be damaged by a 'boil up' - notably rad fan switch. It can cook.

Heres my comparison between a new and worn water pump:

The thermostat may give a cold reading at the temperature gauge due to it being partially stuck open or readings that don't fit the norm - ie it never really warms up properly or in worst (but rare) scenario it is stuck closed leading to no route for water to radiator and the potential for overheating. In the latter case, no matter how fast the fan is going, the temperature will continue to climb. An airlock will also cause this.

Removal Process


As said, you can (if luck is on your side and/or you really enjoy scraping knuckles) remove just the thermostat on its own without disturbing too much. However, I should warn you, its a very tight space indeed and you can only get to it from beneath the vehicle. Much will depend on what exhaust you have as to whether you can get to the two 10mm bolts that hold the lower housing on. Even then, you may or may not have enough room to remove to pull lower part of housing away. Its a very tiny space in which to work.

Start by pulling off hose that joins lower casing and catch the antifreeze in a suitable container. Walk away for an hour so everything dries out.

Beneath the thermostat housing are the two bolts. Get underneath and look up and you'll see the bolt heads underneath the thermostat housing. There is one long, and one short bolt holding it on. I used a tiny socket and wrench (all I could get in there) but even then, you'll only be able to turn the ratchet about 10 degrees each time. Your stat may be really crudded up making removal all the more harder and why an 'overhaul' of pump and thermostat is usually a better route.

With housing pulled away and any water in the pipe draineds remove old stat and seal, clean housing faces (not fun upside down) and fit new stat, spring pointing up and away from you. Press in O-ring and add a smear of instant gasket before refitting cover. It does help keep it in place a little. Now spend ages putting those bolts back, bleeding system for air bubbles and test.

Thermostat & Pump

OK, lets get both out as a unit and do a proper job.

1. Disconnect battery

2. Pulley wheels. Both waterpump and main pulley will need to come off. To loosen their grip (don't remove any yet) you need to overtighten fan belt, stick a screwdriver between alternator fan blades and its casing (don't poke in there too far) and use that as a way to hold everything tight while you free waterpump bolts. Use a big adjustable or socket on a breaker bar if you can get in there, on the main pulley and give it a sharp smack with a hammer to loosen it. Now slacken and remove fanbelt. Undo pulley bolts. Main pulley comes off easier than you think if you lever gently behind it from different angles with a cold chisel. Its only a push fit with a keyway slot.

3. There are essentially four allen bolts (probably rounded out - see below) that need to come out, two on the pump which will test your patience, and another two on the right hand side of the engine thats hold the pipe that goes from left to right and has the dipstick held in place by a small jubille clip. There are three 13mm nuts holding the pump on, and there are those two horizontal thermostat bolts. Theres a short hose which joins bottom pipe to right of bottom pulley wheel - remove right-hand jubilee clip and loosen the hose's grip with a blunt-ish screwdriver.

Expect stuck thermostat bolts (or just one stuck one) which may even require the use of a milling machine to drill out any that won't budge. Its certainly worth trying to see if they will come undone whilst still fixed in the engine as you'll have more to push against but removal will probably require more than you expect. Certainly if you're having to use Hercules strength - stop. The thermostat housing is (I believe) obsolete so treat it like its made of gold. You may need to partially grind away parts of old pump (off the vehicle) in order to remove thermostat housing from pump - then deal with bolts. Don't wreck the housing at this stage. Soak all pump/thermostat bolt heads in plus-gas (not WD40) constantly, particularly when they start to move.

Photo: Thermostat housing removed from vehicle but with a seized bolt (note damaged head). This was eventually removed in a vice with an Irwin damaged bolt remover kit which will bite on to rounded bolt heads. Alternatively you could centre-punch bolt head and drill it out but on a steel bolt in an aluminium casting its EASY to go off centre. Avoid that if you can and under no circumstance attempt this at home with a hand drill. It will not work. You need an accurate setup.

Mullered thermosts.jpg

Photo: Thermostat removed with seized bolt. This was eventually removed in a vice with a damaged bolt remover kit which will bite on to rounded bolt heads. Alternatively you could centre-punch bolt head and drill it out but on a steel bolt in an aluminium casting its EASY to go off centre. Avoid that if you can and under no circumstance attempt this at home with a hand drill. It will not work. You need an accurate setup.

If you do get a stuck bolt in the housing but have at least seperated housing from pump, there are a few ways of tackling it off the vehicle including applying gentle heat or/and a 'damaged bolt remover kit' (mine came out that way).

Heres a short clip showing how I ground away part of pump to split it from the thermostat housing:

If the allen bolts are rounded out, you CAN use a bolt head remover kit on these too but its tight for room and you may need to come in slightly askew and with the tool sticking slightly outside the socket. It worked for me anyway but cost me £22 for the kit to remove one stuck allen bolt. The two left-hand allen bolts on the the pump can just be ground off when pump and thermostat are removed as this pipe will come away with the pump anyway. The right-hand ones are tougher if they're stuck or rounded. An easy-out is a possibility but allen bolts are so shallow, I doubt you'll get any grip without drilling first and there isn't the room. Again, lots of plus-gas (not WD40) will help. My last resort may have been grinding off allen head, removing pipe and using a stud extractor but I wasn't confident there would be enough room, enough to work with or that it wouldn't make matters worse. Just added that in case it had crossed anyone elses mind. I used the damaged bolt head remover kit and it came out no prob.

4. Unclip attached hoses - it becomes obvious which, including the stubby one behind pump, and if metal pipes are undone or loose enough, you should be able to wriggle pump towards you, off its three studs, and remove the assembly by pulling to the left.


1. The thermostat will likely be corroded in and need a screwdriver or small cold chisel to get it out. Clean all casting faces very carefully, removing deposits and any old gaskets before fitting new thermostat.

2. You'll need instant gasket, using a thin smear at major joints for a watertight fit. Consider replacing short stubby hoses with new. Fairly sure they're 32mm ID. Silicon hose would be great.

3. You slide thermostat and pump (as one unit) on to the two metal pipes, leaving long metal pipe loosely bolted on the right to give you enough room to do this. Poke the one with the rubber hose attached back where it came from. Its annoying, but it will go once you have pipes and pump lined up with its three studs.

Use instant gasket around pipe that has the small O-ring - you do not want to chance leaks there. That O-ring has a habit of staying out so check carefully that it DID go in with pipe and its not hanging out somewhere. Instant gasket will help it slide in and help seal it properly. You can also squeeze some into the space around the pipe afterwards.

4. Fit NEW allen bolts. DO NOT put the old ones back please. You could fit slightly longer ones, screwing a 13mm nut on them so it sits underneath the head. This would then give you TWO ways to get them out in the future.

5. You'll need to fill and bleed the system with plain water to make sure it doesn't actually leak, before draining and refilling with the 50/50 antifreeze mix. If your engine got very hot, change the oil.

6. Do not push yourself and don't attempt this job in the hope you'll be at some camper meet the next day. You will be disappointed.

7. Just pay someone else to do it - its a horrible, nasty, contemptuous job and there will be plenty of moments when you'll contemplate removing the engine in desperation or even suicide. Its not nice.