Misterious overheating

[Sharky]

So, forst of all I have a 1996 Peugeot 205 GRi with a 1.1L engine. I rarely take it out of the city But a week or so ago I went to my girlfriends country house in it. that house is located at a lower altitude hence the temperature is higher. When I was coming back, through an uphill mountain road in good condition with moderate traffic at about 40-50 kmph mostly in second gear,when I got the emergency lights that warned of overheating. The car doesn't have a needle instrument for temp (as many low end french cars) so the only information I had came from the light. I stopped, waited for it to cool and started again but 10 minutes later I got the light again. Stopped, waited for it to cool off and by then the atmospheric temperature started to cool off and there was less traffic which meant that I could continue my journey at about 80Kmph in 4th gear without any problems.

Thing is that it's the third time it has happened and the other 2 times it was under the exact same condition. First time was 3 years ago. Once again going to a friend's country house, taking an uphill mountain road under a hot climate. Halfay through I got the lights. The other time was last year going to a nerby town. Once again, uphill mountain rouad, an unusually hot day and I got the lights.

But these have been the only situations under which it has happened. The city where I live is relatively cold all year long and it never happens. I could be stuck for hours on a hot day in a traffic jam and I don't get the lights. It is the combination of a climb, hot day and moderate speed.

Does anyone have any idea what could be the problem?

[HiRich]

So to summarise:

Problem appears when climbing fairly slowly - higher ambient, slow speed, high load (climbing, possibly more weight?), low gear, presumably reasonable engine revs.

Problem does not appear when climbing faster - lower ambient, similar load, presumably similar revs, higher velocity

Problem does not appear in static/slow urban, although with cooler temps.

However, in all cases, we only know the situation has gone critical (light), not whether it is going near critical (no guage to tell us if temps are getting rather high).

From my days of cooling tests:
- Tests are done on a wide range of conditions: static, soak after switch off, high speed, high loads (climbing) at different speeds.
- Every installation is different, so the most critical test will be different.
- Ambient temperature has an almost direct correlation to coolant temp (and extra 5 degrees on air temp adds 5 degrees to water temp).
- The system should be good for at least 35 degrees ambinet temp on all tests (as new). Some tests will be good for more than 50 degrees.

First question then: When you have the problem, do you have any idea of the ambient temperature? It is possible that you are just in a very extreme environment.

The problem appears to be a situation of high load (climbing), decent revs (so decent coolant flow), low speed (so low airflow) topped with high ambient. This suggests to me that airflow across the radiator is the weak area, though other issues may be contributing. Given that static work does not cause a problem, it does not suggest to me that you have a major problem (e.g. a failing pump). More likely, I would suggest that either the conditions are too extreme, or several small elements are reducing performance, so my advice is to consider each element one-by-one, in the following order:
1) Coolant: What's the mix? I would certainly consider a good flush of the system, and a fresh mix.
2) Oil: Check you have enough. Low oil will raise both oil and water temps.
3) Radiator: Worth checking for leaks. Also sludging (so flush it) and blocking on the airside (inspect, pluck off crap, wash & hose it down).
4) Thermostat: Possibly stuck part open, restricting flow. Without a gauge, you can't tell whether it takes rather long to warm up. If it's easy to remove, pop it out to look, and it's probably cheap enough to just change.
5) Engine tune: Is it right? If it's running lean, combustion may be a bit hot = more energy to dissipate. Could be relevant given the loading conditions where the problem occurs.
6) Fan: Does it cut in properly (easiest to hear when stationary, rather than thrashing up a hill)? Presumably it's electric. If it does when stationary, we can assume it does on the hill, and the sender is fine. When it does cut in, does it spin at a decent speed and freely (motor working OK)?

And on the fan, there are two options to consider:
A larger, more powerful fan
A manual override of the fan sender, with a switch on the dash. Keep the sender wired in, for automatic control, but the switch would allow you to pre-empt it, if you are suspect the temp is rising.

Finally, if you decide to accept the problem as a rarity, or the other changes haven't solved it, one workaround for when you pull up to let it cool down:
- Pop the bonnet, to let the hot air escape.
- After five minutes (a fag break), restart the engine and rev it for 15 seconds. This will move hot coolant in the block out to the radiator, and cooled water back into the block. Overall, you will shorten the cooling time. If you have fitted a fan override, switch it on while you do this.
- Repeat this a couple of times. In 10-15 minutes, you will have dumped a heck of a lot of energy efficiently, and you will be able to go quite a bit further before the problem recurs.

[Sharky]

Thanks for your answer.

The ambient temperature was high but hardly extreme. I believe that it was below 30°C. There's enough oil and also enough coolant. There is a slight leak in the system located at the dashboard heater but it means that I have to refill about once every 2 months. And it was filled when it happened. The fan does seem to work fine as it starts up and powers off fine. The engine was last tunes 10 months ago I think but I haven't noticed any strange behaviour.

What strikes me is that it seems to happen to this car only. The other day we came back from a long trip from my mother's hometown in my dad's Mazda protegé 1.6L. 7 Hours of hot climate, steep uphill mountain roads with moderate traffic. Hardly took the car below 4500 RPM but the temp. needle never moved above the middle.

[HiRich]

Every car can be different, even two different engine installations in the same chassis. The Mazda may have a radiator more suited to the car/engine (larger, more efficient). Equally, the larger engine, presumably more powerful, may just be less stressed climbing the same hills. It all comes down to how much heat is being generated by the engine in a particular load/speed situation, and how the system removes that energy - first to the water, then to the air, then extracting the hot air).

Having said that, given the things you say are OK, a limit of about 30 degrees ambient does not sound particularly good (even allowing that the conditions may be beyond what Peugeot design for). Your car is ten years old, though, so I would certainly give the cooling system a damn good flush (and refill exactly on spec). If you can access them, pop off a few hoses (especially radiator bottom), stick a finger in, and see if you can feel any gunk. Although perhaps well-serviced, you don't know whether they have changed the fluid, and they probably haven't flushed it. The fine tubes in a modern radiator can become clogged, and that can significantly reduce its efficiency.

While you've got the system drained, you may as well change the thermostat (as I say, presuming it's cheap and easy to access). And as mentioned, check and clean the airside of the radiator.

If you can get it, you might consider a product like Water Wetter, which you add to the coolant. This reduces surface friction, allowing the coolant to move more swiftly around the system (and so extract more heat). I'm not totally convinced, but others on here rate it.

I would consider these things as 'maintenance' work. Each might give you a few extra degrees on your ambient limit (and hopefully together lift it far enough for the problem to disappear), and bring the car closer to ex-factory condition.

As to more serious issues, it doesn't sound like the water pump is the problem. It doesn't sound like the vanes are damaged (I would expect the static work to show this up) or that the drive (belt?) is loose. The heater leak is not exactly good, especially if you have lower air pressure, but this should not really affect cause the light to go on, rather allow it to boil at a lower temperature. And I come back to the radiator clogging up.

If these don't help you, I'm starting to struggle. It is possible that your car's spec (with some degradation over a decade), just isn't up to the job. If you really need to solve it, and the above hasn't done the business, you could consider:
- A new radiator (to standard or uprated spec)
- Can you swap in the system from a larger engine (the 1600cc model)? You might assume that Peugeot would use the same installation for both, but it is quite possible that they used a smaller, cheaper radiator on the 1100)
- Add an aftermarket, larger or double fan

Unless I'm missing something