Coolant Temperature needle and light

[Roydini]

Right. I've found all sorts of bits and pieces relating to this over many different threads, and in the Wiki but I would like to try and put a list of things together that people recommend I check after the problem that arose yesterday.

For the first time since I bought the van almost 7 years ago I noticed yesterday whilst out on a short drive that the pressure gauge needle on the dash had risen above it's 'normal' position. Almost immediately after I noticed this it continued to rise quite quickly, until when at roughly 12 o'clock, the red light came on. I immediately turned off the engine, pulled over and sat for 10 minutes to let things cool down and ponder the problem. Fortunately I was not far from home and was able to get close enough to park up just as the needle and light came on again after 1 mile or so.

First of all, can I confirm what exactly the gauge is reading? It's the oil pressure right? Or is it the coolant pressure? And is the red light just a warning when said pressure gets dangerously high? I'm a little unclear about this as I've seen many people refer to it as the oil temperature gauge? I have a separate VDO oil temp gauge connected to a sensor built into the engine sump drain plug and this was sitting at the 'normal' 90ish degrees C.

I would really appreciate it if anyone can suggest what might be at fault, and what things I should check.

At the moment I am thinking

Check Alternator belt
Replace 'Dalek' Cap on Coolant Header tank (the one in the engine bay)
Check around engine and coolant pipes/radiator for any obvious leaks.

What else should I be checking? A more thorough and logical list would be really useful!

Thanks very much in advance folks - I want to be careful here and not destroy the engine!!

[SamsBus2012]

As with all my postings, I'm no expert but it was always my opinion that the top guage was for coolant temperature and the redlight was for low coolant level - correct me please if I'm wrong and sorry for hijacking the thread!

[marlinowner]

The gauge is coolant temperature, the light built into the gauge flashes as a warning of either low coolant level or high coolant temperature. Check the coolant level in the reservoir with the dalek cap, it should be full. Coolant level in the tank behind the number plate should be between Max and min.

[ghost123uk]

I noticed yesterday whilst out on a short drive that the pressure [temperature] gauge needle on the dash had risen above it's 'normal' position. Almost immediately after I noticed this it continued to rise quite quickly, until when at roughly 12 o'clock, the red light came on

Hmmm, that temperature gauge is supposed to sit at around 12 o'clock normally. Then rise above that if the engine starts to get too hot. Then, when it gets to about 3/4 up it's scale you should here the radiator fan kick in, it is quite noisy so you should hear it.

Bearing in mind the recent hot weather :-

In past months, where has the needle on that temperature gauge sat ?
How long was this drive and were you stuck in traffic at any point ?
Have you heard the radiator fan come on at all, ever ?
Is the coolant in the left hand white tank (the "header tank") full to the brim ?

I immediately turned off the engine, pulled over

Is the RIGHT thing to do, but so many folk don't !

I want to be careful here and not destroy the engine!!

Very sensible.

[Roydini]

Thanks for the replies folks. Ok, I now understand what the gauge/light represent. Needle is coolant temperature, and red light is a warning when coolant level gets too low and/or coolant temperature gets too high. Thanks for clearing that up. I had heard people talk about an oil pressure light but probably I have confused that with this red coolant level warning light. The oil pressure light is the one in the central display, next to the full beam light and indicator light I presume?

Anyway, I checked the coolant level in the header tank and it was not absolutely full to the brim, more full to the neck of the cap. I have topped it up with distilled water (roughly 150ml) until it was spilling over the sides, then cap back on. BTW I have the old style header tank with the twist-lock cap, and not the newer dalek style one. I think Simon from Brickwerks describes these older caps as "rubbish". Perhaps the cap is at fault and no longer maintaining the correct pressure?

In past months, where has the needle on that temperature gauge sat ?How long was this drive and were you stuck in traffic at any point ?
Have you heard the radiator fan come on at all, ever ?
Is the coolant in the left hand white tank (the "header tank") full to the brim ?

Since I bought the van the needle has sat between the thick white line at the extreme left of the gauge and the thin white line roughly 5mm to the right. After 10 minutes or so of driving the needle sits exactly on this thin white line. I have never before seen it rise to 12 o'clock or to go beyond the position of the red warning light for that matter, nor have I ever had that light turn on, except of course when turning the ignition on.

The drive was about 20 minutes on main roads and highways so no traffic jams.

To my knowledge I have never been aware of the radiator fan coming on. Ever. In 7 years. Could it be possible that I just never noticed it? Is it very noisy? Or is that my problem right there?

I'm about to perform the cooling fan thermoswitch test with the paperclip, as described in Haynes and hopefully ascertain if either the switch or fan are at fault.

[ghost123uk]

OK, so if you were driving along it is less likely to be the radiator fan or it's switch, relay and fuse at fault. But, go ahead and test it anyway. There is more on testing it in our "wiki" (link at top left of every page on here).

However, if your gauge has never moved up to somewhere near the middle, either you have a faulty thermostat or a faulty gauge. Does your fuel gauge work OK (they are connected) ?

Re thermostat. Have a good read around on here researching replacing the stat on the earlier cooling system. The housing it fits in at the water pump is notorious for the screws getting seized in place. If you damage it trying to get them out I understand they are hard to come by (but someone might now be doing them - anyone now ?)

With a bit of luck, Raph, "CovKid" on here will be along soon. He is well experienced with replacing parts on the earlier cooling system (note = if you contact him, ask him to post on this thread for all to see for the sake of future searches)

[Roydini]

Thanks for the feedback Ghost123uk

So, a little update:

Did the paper clip test on the cooling fan thermoswitch and the fan failed to switch on, fast or slow. That'll be buggered then. No great surprise as to my knowledge the fan has never come on in the 7 years I've had the van.

Fuel gauge is fine, not super accurate, but fairly constant it its inaccuracy!

Checked auxiliary belt -Ok

Checked and cleaned up all electrical connections and earths

Removed coolant level sensor from top of header tank and gave it a clean - it was pretty grubby and had small yellowish/white deposits on the two probes. A drain/flush/replacement of the coolant system was overdue and probably going to be necessary to get to the bottom of this anyway so I'll start thinking about that regardless.

Removed old style, non-dalek type cap from header tank and cleaned it up.

Fully topped up header tank again until overflowing, then cap straight on.

Checked oil level (whilst cold) - bang on half way up the dispstick.

Turned on engine and gave it a few revs. Checked belt again with engine running and made sure coolant pump pulley was turning.

Hit coolant pump with a hammer. (Partly out of frustration!)

Then went and sat in the cab.

I watched the needle rise slowly but steadily to about 11:30 o'clock (just before the LED) whilst simultaneously keeping an eye on the VDO oil temp gauge. At about 80degrees C on the oil temp the needle rose quickly past the LED, which then lit up and continued to rise until and I promptly switched off the engine.

Left everything for 15 minutes to cool down, then went back to engine bay. The header tank was roughly 3/4 full? As the coolant cools it should suck the excess back up the hose from the top-up tank behind the numberplate flap right?

So, as I understand it the problem could be the header tank cap not keeping pressure (seems to be a common problem), or maybe the thermostat is buggered and not directing the coolant to the radiator after it gets above a certain temperature?

any other ideas or suggestions?

[nevill3]

When my thermostat failed on my VW Polo I found that by turning the heating onto full heat and having the blowers turned up high reduced the temperature and allowed me to get home without boiling the engine. Not totally relevant to your problem but a handy tip for people with faulty thermostats as an emergency get to a safe stopping place. If you try starting yours again and have the heating on full with the fans on high and it slows the overheating problem your having I would think it is a thermostat problem.

You didn't say whether there was any water in your top up tank, but presume you checked it.

[123-jn]

when the temp hits 80 degrees does the radiator feel nice and hot? You can get at the top by removing the grille. If the rad is hot and the temp is still shooting up then this is when your fan should cut in (at about 87-89 degrees). If the rad is not hot suspect an airlock or probably a stuck thermostat. Loosen the bleed bolt on the left of the rad as you look at it and see if there is any air to expel? If not next I would change the stat, on refilling just use water incase there is still an issue (you dont want to waste 8 litres of antifreeze). (have you checked the fuse for your rad fan? you never know your luck) The expansion cap can make a difference although usually it just runs too hot not normally dire emergency stuff.

[timjwharton]

Also worth mentioning (see Wiki) that there are a number of reasons what the red light of doom may be flashing. I've had this problem on and off for years, and am convinced more and more it's a PCB problem rather than anything else...

[Roydini]

Thanks for the comments folks.

Went out and had another poke around tonight. Firstly I topped up the header tank (again) and triple checked the level on the top-up tank behind the flap - it was just under maximum mark.

Then I started up the engine and left it ticking over for a few minutes whilst giving it some revs.

Went to have a look at the engine bay and noticed that the header tank level had fallen back down to just above the MIN mark.

Went back to the cab and almost immediately saw the red light start to flash and the needle shoot up again, so switched off straight away.

Removed front grill and checked the radiator, stone cold, ie i could touch it with bare hands and couldn't detect any heat top or bottom.

Went back to engine bay and header tank level was still sitting around MIN mark.

So, I think I can draw the following conclusions:

1. The fan is buggered on the radiator - this I had already confirmed with the paper clip test as described in Haynes.

2. The thermostat is buggered - it should open after a certain temperature and allow the fluid to circulate through the radiator.

3. The header tank cap or coolant level sensor o-ring is buggered - ie there doesn't seem to be enough pressure to suck fluid back up from the top-up tank after coolant begins to cool.

4. The water pump is buggered - it doesn't seem to be circulating the fluid around the system, although perhaps this is because of the thermostat???

5. The water jacket seals are buggered - I must have topped up the header tank three times now with perhaps a litre of water in total - where is this extra water going? There are no obvious leaks and the top-up tank level hasn't changed by any discernable amount? Is it boiling off somewhere - I never saw any steam or anything? Is it leaking into the water jacket? Or worse? Leaking/cracked cylinder head?

Anyone got any suggestions what the likely culprit is?

[CovKid]

As Ghost said, I came along.

I suspect that the reason you're topping up and level still drops is you have air in the system and it needs bleeding. If theres not enough there may not be much if any water in rad so it won't get hot. Firstly, follow this (keeping an eye on temperature):

http://wiki.club8090.co.uk/index.php/Co ... ing_system" onclick="window.open(this.href);return false; - 2,500 revs should annoy the neighbours a bit if you're doing it right. If its not revving fast enough you'll never bleed it.

Secondly, have a read here: http://wiki.club8090.co.uk/index.php/Co ... overhaul_3" onclick="window.open(this.href);return false; which was my experience working on the earlier cooling system.

Its possible to just change the thermostat (may be faulty which could cause your problems) but note my comments about gaining access.

[Roydini]

ooft! Thanks Covkid! Very interesting and thorough account. I actually had the water pump and thermostat in my basket on Brickwerks and was about to pay for them when you replied! It sounds like an absolute nightmare job and the sort of thing I will mess up somehow or other. Contemplating trying to get the thermostat out on it's own though i appreciate your comments about doing a proper job etc.

First off i'll bleed the system tomorrow and eliminate that problem. I'll try and get a socket into those thermostat bolts and see how feasible it looks and go from there.

One other thing, whatever happens I'm going to be flushing and replacing the coolant at some point very soon and I just wondered where people stand on draining from the water jacket drain plugs, or leaving them well alone and just undoing the lowest hose clip and draining from there? The later seems easier to get to as you don't need to faff around accessing the drain plugs, but does it achieve as thorough a 'flush'? I still have the greeny-blue coolant which has probably been in there for years so would be good to get it all out before refilling?

[CovKid]

Pull hoses - way easier. You could always use a garden hose or similar to force muck out. I used a flush treatment a year or so ago, taking it for a 20 mile run with that and plain water to disturb sediment etc but in hindsight I don't think it was worth the effort. Its just as easy to use a hose if you really want to clear passageways through. Definately do that first and don't worry too much if in doing this, the antifreeze levels are not what they should be - you're really testing to see if an airlock is there and whether you can clear it.

When you are happy that system holds water and airlocks are gone, you can set about draining and refilling with longlife (pink/red) antifreeze.

Good idea on checking to see if thermostat housing bolts will move. The other two bolts on the housing (10mm heads accessible from underneath) where the thermostat lives, will come undone ok if you decide to just fit a new stat. They don't seem to be subject to seizing.

Its worth removing fanbelt and checking for wear in waterpump - you'll feel it rock about if there is any. https://www.youtube.com/watch?v=LghNy400HzI" onclick="window.open(this.href);return false; - you'll only detect it with belt off. You can then decide if the best option is a complete overhaul as I show in the WIKI. Clearly replacing pump and thermostat (arduous as it is) removes that problem from the equation but no sense in changing pump if there is no real play in its bearings.

Chris (CJH) is about to do his so it might be useful to at least lean on each other if you go the overhaul route. I'm happy to advise if you hit a problem ofcourse. Do take pics if you encounter issues as I can add those to the WIKI. You may hit probs I didn't, or if lucky, none at all.

My hunch is you've hit all the issues I had and it may take some work to get everything functioning correctly but once sorted....

[CJH]

Pull hoses - way easier. You could always use a garden hose or similar to force muck out. I used a flush treatment a year or so ago, taking it for a 20 mile run with that and plain water to disturb sediment etc but in hindsight I don't think it was worth the effort. Its just as easy to use a hose if you really want to clear passageways through. Definately do that first and don't worry too much if in doing this, the antifreeze levels are not what they should be - you're really testing to see if an airlock is there and whether you can clear it.

When I drained and flushed mine I'm certain that I didn't get all of the old coolant out - probably not much more than half in fact. I suspect the head drain bolts would have helped. I disconnected various hoses and jammed a garden hose in with a rag to flush everything through, so I'm pretty sure all traces of the old coolant were gone, but when I connected everything up again it was a bit of a struggle to get all of the new red coolant in, because there was so much plain water still in the system. During the bleeding process I was adding neat coolant and eventually I got it all in, but it means there was about half the system's capacity still trapped in the system when I started.

Chris (CJH) is about to do his so it might be useful to at least lean on each other if you go the overhaul route. I'm happy to advise if you hit a problem ofcourse. Do take pics if you encounter issues as I can add those to the WIKI. You may hit probs I didn't, or if lucky, none at all.

Yep - new water pump on its way, new thermostat in hand (will test it in boiling water before fitting), and a good, clean thermostat housing sitting here waiting to go on (wasn't cheap, but it takes a bit of uncertainty out of the job). Various new gaskets on their way too, together with a new rubber O-ring for the metal water pipe and a tube of Dirko seal. I've also ordered new allen bolts from here. The originals are M8x23 (measured to the underside of the flanged head), so M8x25 with washers should be the equivalent. I've also ordered some at M8x30 and some nuts, and if there's room I'll copy Covkid's idea of putting the nuts under the heads for a bit of extra insurance in the future.

Strictly speaking this isn't a necessary job on my van yet, but having bought the thermostat housing with the intention of carrying it as a spare for when the pump fails, and since I have some dismantling to do in this area anyway, it makes more sense to overhaul this area in the comfort of my drive - one less thing to go wrong on my hols. Might be tackling this on Sunday, depending how far through Saturday's list of jobs I get