Identifying overheating problem

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Wookey
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Identifying overheating problem

Post by Wookey »

I have a 1997 Peugeot Expert 1.9D (camper sefl-conversion) with a 1994 Xantia TD dropped in.
It's still a very reliable (if smoky and ancient) machine.
However last 2 years I've noticed that it overheats if you get stopped on the motorway on a hot day. The gauge gets over 100C and the coolant tank cap tends to let off a bit of overpressure so it loses a bit of water. And then the 'STOP' light starts flashing at me.
It's fine most of the time. So I think what is happening is that my cooling system is just not as efficient as it used to be, and hot engine, crawling on motorway on hot day is pretty-much the worst-case for normal use (which is why we used to see lots of overheated cars by side of road in these circs - rather rarer these days).

So advice on working out what's up would be welcome.

I tried running it on the drive to check that the fan came on as expected and cooled things down. The fan is controlled by the 2-position switch on the side of the radiator. I get two fan speeds if I short 1-3 and 1-2. Leaving it idling it warms up as expected and when the dash gauge gets to 93C the fan comes on (slow). Then off after 20-45secs, then on after 45s-1m30s and so on. So it seems entirely stable under no load at that temp, and able to cool itself with only low-speed fan on maybe 1/3rd of the time.
Presumably things would start to go awry if the fan ran 100% of the time but the temp still rose? But then we should have speed 2? I need to take the sensor out and check that it really does switch the 2nd speed at the correct temp (100-102C according to my Russek book). But assuming that's working, what else might be causing overheating?

I note that my fan-mount has space for 2 fans but only one is fitted on this car. Anyone know which models have two fans? - is that for the TD as opposed to the D so I should have added one when I upgraded? (It looks like a spare C15 fan I have will fit with a bit of cable adjustment - I guess I can just put them in parallel and that will work. (checking fuse is sufficient)).

On previous antifreeze changes the stuff has always come out pretty clean and I did once put water through the rad backwards but didn't get any mank out so there has been no obvious corrosion of sludge in the past. I'll do that again this time, and it has been significantly more than the regulation 2-3 years (although the car didn't move for 15 months in the middle so I'm not sure how much that matters).

Here is the temp/time plot I generated from running it at a fast idle until the fans came on (and cycled 3 more times).
http://wookware.org/pics/online/frenchcar/temptest.svg

The radiator itself looks OK. There is a little bit of white corrosion on some of the fins, which I presume will be reducing heat loss, but it doesn't look bad for a 25-yr old radiator. Here is a pic: http://wookware.org/pics/online/frenchc ... iator.jpeg

I did note that the top-hose warms up quickly, whilst the temp gauge is under 50C, so that make me think that my thermostat is stuck open. It should stay cold until the engine temp gets to around 80C, right?

Because the engine has been swapped there is some question if the sensors are wired up right. There are two sensors in the top of the thermostat housing. Only one (drivers side) is connected, and I presume is the dash temp gauge. I think the other is an on/off switch, maybe for an overheat light? But the wiring harness for the 1.9D van didn't have anything for that so I just left it unconected. But it's been like this for 18 years, so is not the cause of the overheating, which is new in the last 2 years. How does the gauge work. is it a changing resistance and the sensor/gauge are matched?

So, what do we think of all that. What else would you check? How can I reproduce/test the problem when it only occurs on hot days/long drives/lot of stuff?
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myglaren
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Re: Identifying overheating problem

Post by myglaren »

In the first instance, as everything other than the thermostat seems to work as it should, would be to use a cooling system flushing agent, such as Forte Cooling System Flush.
Can be hard to get in normal retail places but eBay and Amazon have it.
Alternatively, another recommended one is Liqui Moly.

If the thermostat were staying open, or opening too soon, that would largely negate the problem. Perhaps it is stuck part way and never fully opens or closes.
Worth investigating.
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xantia_v6
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Re: Identifying overheating problem

Post by xantia_v6 »

I think that you may have a failing head gasket.
RichardW
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Re: Identifying overheating problem

Post by RichardW »

They pretty much come installed as std on the 1.9 TD! That was my thought too; check for pressure in the cooling system when cold, or rapid pressurisation after cold engine start.
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Re: Identifying overheating problem

Post by 20th Century Pug »

I presume you already know the importance of careful bleeding the XUD cooling system? Otherwise air locks can cause hot spots in the head. Worth opening the bleed screws to check for trapped air.
Wookey
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Re: Identifying overheating problem

Post by Wookey »

OK. So I took the thermostat housing off and was pleasantly surprised not to have any seized bolts. The old thermostat (marked '93 so presumably
original) still worked in that it opened somewhere round 80C, but it never fully closed, which fits with the top hose warming almost immediately after engine start. So I replaced it (bit of a game getting the right part and gasket - bizarrely the ECP thermostat only cost £2.16, but the gasket was a fiver - still very reasonable ). The new one actually closes so that's all better than it was. The engine does not heat up as it should, but clearly that's not going to make any difference to my overheating. Mind you we spent a warm tedious hour in a trundling M25 queue a couple of weeks ago and it didn't get too hot. But it wasn't roasting and we were moving so not worst case.

My coolant come out lovely and clean blue so no obvious corrosion/sludge. I tried reverse flushing and got a little bit of crud out but nothing at all significant.

Pity I didn't read that comment about the Forte flush before draining. Can you just refill with plain water and that stuff to do a flush? (I do have the old coolant in a bucket so could use that as flushing agent if needed).

BTW where does one take old coolant these days? Our local tip doesn't take it any more. Beg a garage I suppose.

I've also fitted the missing second fan. It seems the 2nd-fan relay is already fitted (I can hear it when shorting the sensor pins). There are three different 2-fan wiring diagrams in the Russek book and I've not worked out which is mine yet. Going to see if I can get it going now.

Re bleeding, the Russek book says there is a bleed valve on the heater matrix pipes, but I can't find it. I'm fairly sure it's not fitted on mine (unless it's on the interior side of the firewall). It _seems _ to fill fine from just the expansion tank, (which is just about the highest point) and the radiator bleed. It was much fiddlier on the old C15 with a couple of pipework bleeds.
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myglaren
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Re: Identifying overheating problem

Post by myglaren »

What do you do with waste engine coolant?
They advised that small quantities can safely be disposed of by flushing down the toilet. It will be such a small concentration that sewerage works will be able to handle it. It should never be poured down drains, as it will go direct into water courses.
Wookey
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Re: Identifying overheating problem

Post by Wookey »

OK useful (who was 'they'?) The drains and toilet go to the same pipe in this house so that's easy.
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myglaren
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Re: Identifying overheating problem

Post by myglaren »

By 'drains' they mean the grates in the street gutters.