New thermostat and now problems!

[Matt and Danni]

Hi all - I have a 1.6 CS diesel and am in need of a little help!

I have replaced the thermostat - the temp was originally getting a little hot early on in journeys, before returning to normal. I thought the thermostat could be sticking.

I've been bleeding the system as per the brickyard method, but can't seem to get the thermostat to open. Bleeding is fine, all bubbles out and clean coolant flowing from the rad bleed screw - it gets luke warm after a while - I guess from coolant eventually flowing to the rad via other pipes?

I took the thermostat out and bled again - coolant flowing nicely, radiator getting evenly warm.

I ended up buying an IR thermometer and checking things with the thermostat back in (tested in a pan and it works) - the same thing happens again - the coolant isn't getting hot enough at the water pump (where the thermostat is).

Temps read up to 104 degrees on the head and coolant junctions (the temp sender is off the back of the head, to the heater matrix).

Temps on the coolant pipes range from about 87 in the big pipe just off the head, to 65-70 ish at the water pump.

Temp gauge is reading just over halfway, and rises if you take it for a drive.

Things maybe useful to mention:

Heaters are getting hot

Radiator is about a year old.

Virtually every coolant hose has been replaced

New temp sender

Pressure cap is holding pressure.

Head gasket was replaced a year and a half ago - would hate for the same thing to have happened again!

I've been scratching my head for a while now - I would be so grateful if anyone could help shed some light on the situation or suggest some ideas

Thank you

Matt

[Smcknighty]

How far does the gauge rise? How soon does it get to midway? Stat is designed to get the engine up to temp (which is midway!) and it's fairly cold out at the moment.

How old is the pump?

[Matt and Danni]

Hi Smcknighty,

Thanks for replying - The gauge sits on the LED, at the right hand side. I think this is normal, however it used to sit on the LED, at the left.

It gets to midway roughly after 20 mins idling.

The pump is about a year old, seems to work fine - the impeller spins with the pulley and there is no play. Coolant can be seen to be circulating when toping up the header tank.

Thanks

Matt

[Smcknighty]

It doesn't sound like there's anything wrong? There's a lot of water in there to heat up? I spent a lot of time chasing ghosts on mine once to find it was a dodgy temp sensor, and the belt tension which I sorted fairly early on.

Why did it blow its gasket in the first place?

[simoncummins]

Yea that sounds right.

[Matt and Danni]

Thanks for replying - I've just taken the van for a short drive. The temp needle got to 3/4 on the gauge, the rad was still stone cold, the thermostat hadn't opened. No air was coming out of the rad bleed screw, just coolant

Using the IR thermometer, the head was max 108 degrees but yet a lot colder in the pipes - seems strange to me

I'm not sure why the head gasket went in the first place. The pipe coming off the head at the top of the first bend actually sat higher than the header tank - the first thought was that it could have been a place for a recurring airlock and maybe a reason why the gasket went

I'm thinking about getting a digital temp sender like this one for an accurate reading

http://www.ebay.co.uk/itm/NEW-2-52mm-UN ... 5b08ac1432" onclick="window.open(this.href);return false;

The temp sensor is new, but I have another to try. The water pump pulley is tensioned so you can turn it about 1/4 of a turn, would this be about right? Coolant seems to be circulating and the belt isn't slipping

Thanks

Matt

[Smcknighty]

Ok it's not sounding right. Should stay in the middle. You can turn the pump?? That doesn't sound right? How did you tension the aux belt?

[Smcknighty]

K according to Bentley the tension of aux belt should be 2-5mm deflection on a belt less than 1000mm long, 10-15mm on longer belts
This is thumb pressure. The first figure for a new belt, the second for an older belt.

[Matt and Danni]

You can turn the pulley on the pump by hand which turns the impeller (saw it turing through the hole for the thermostat housing).

The aux belt is tensioned from the alternator, pulled it as much up as I could and tightened the bolt.

Thanks

Matt

[Smcknighty]

I'd try another stat - new ones can be duff as well, boil up the old and new along side each other, watch what they do? It's mechanically simple, if you can get the rad hot without a stat you should be able to do so with a functioning stat (e.g coolant is flowing). It sounds like the engine is getting too hot (or the sensor is duff)

One final thing - your fuel gauge work ok?

[Sir Brixalot]

Might be worth checking the bleed ring that runs around the top of the engine bay. They can block especially on the T that runs to the LH side head. Not trying to teach you to suck eggs but is the thermostat in the right way round?

[CovKid]

Matt, mine does this. On my old thermostat, the temp needle barely got off the cold mark but when I fitted a new one, it'll go to just right of the LED (ie just past it). It never goes any higher. I also gather thats normal but I was happier with it sitting lower than this. The swing from hot to catastrophe seems a small one given where it can sit in traffic.

However, its surprising just how much you have to rev it during the bleeding process to actually expel trapped air in bends etc. Took a few attempts I found and next to impossible on your own. When I'm moving it'll sit below the LED. As soon as I'm in traffic it'll go to right of LED. Heating seems fine for a vehicle that has long pipe runs.

I do have a chicken switch if I ever end up in a tailback but it never seems to go higher than that. Switch is more for peace of mind.

Its worth noting that regulation of temperature on T25s is by no means exact but yours does sound normal. At some point I'll fit the VR6 stat someone mentioned which kicks in a little earlier but not so bothered over the winter.

[ghost123uk]

Might be worth checking the bleed ring that runs around the top of the engine bay.

If Diesels have that bleed ring then yes, good advice. Mine was blocked a few years ago and caused overheating grief.

They can block especially on the T that runs to the LH side head.

But note this is a Diesel van, so no left hand head but you are dead right re petrol engined vans

[Matt and Danni]

Hello all.

Thanks for the amazing replies. I hope everyone has had a great Christmas - I've been away for a bit and not had access to a computer to come on here.

I tried a new thermostat again to no avail, but then after reading somewhere (I forget where) I tried drilling a small hole in the metal ring of the thermostat. I guess this aids bleeding? I'm not sure if I just wasn't bleeding the system properly before (I was bleeding it for a long time following the brickyard procedure) but it seems to be working as it should now.

It seems that the system was getting too hot previously only when driving, but the temp of the coolant at the thermostat wasn't getting hot enough. I still can't figure this one out - maybe an very stubborn airlock stopping flow? It appeared that the system was bled but there's a lot of pipe I guess!

I'm hope that drilling a small hole in the stat has just helped bleeding and is not hiding another problem?

Thanks so much for all the help!

Happy Christmas

Matt

[Matt and Danni]

I forgot to mention - the fuel gauge does work.

Are the fuel gauge and temp gauge connected somehow? Through the PCB?

Matt