Overheat Warning but Gauge at 75

[Pug_XUD_KeenAmateur]

My coolling electronics are doing really weird stuff. Any ideas? Pug 405 na
As follows.....

Drive 5miles ish, narrow rural roads, pootling along 40-50mph, cool weather, no thermostat fitted, gauge doesn't make it beyond 75c
Arrive at destination (Jumble Sale) browsing an outside sales area just in front of where I've parked, I hear the fans come on.... that's weird.
Ok... jump in, put the key in, turn it to aux, fans remain; turn it to ignition, still on, temp about 70c, fire it up, they go off in the moment that the starter's taking the juice and remain off. Run it just a few seconds at a fast idle. Check temp's still fine. Switch off. Fans come back on.
Open bonnet, check engine & various hoses temps, all cool, remove battery + and go browse jumble.

Return 30mins ish later
Commence homeward
2miles down the road, steady 45mph, the oblong 'Stop' flashes on & off repeatedly about six times, and the overheat warning on the temp gauge is flashing too, fans come on fast about mid way through the light show and go out about 10secs or so later. Temp just over 70.
Check hoses, thermostat body, etc, all well within normal range. Rad itself is of course all but stone cold.

Makes no sense.... How can I have the red overheat warrning flashing on the same gauge that's reading 70c?! Surely they're served by the same Sender?

Battery currently disconnected: who knows whether it'd be flat in the morning elsewise?

NB: anyone else seen this, a RWD Peugeot 405 ROA, which it seems is essentially a 405 with Avenger running gear, Iranian market. Very strange idea. https://www.google.co.uk/url?sa=i&rct=j ... 9517755281

Could it be Hurricane Doris, now passed, residing under my bonnet?!

[white exec]

Many of these engines have no fewer than three temp sensors:
1 - feeds the gauge
2 - sends coolant temp to injection/engine ECU
3 - feeds water temp control unit, including over-temp dash warnings
If you have twin fans, three relays take instructions from #3, and switch the fans on
- in series for slow speed
- in parallel for high speed.
For a single fan, a couple of relays switch the fan on/off and a resisitor in/out to achieve the two speeds,
Hopefully someone can follow up with a circuit diagram.

[Pug_XUD_KeenAmateur]

thanks Chris, so its probably '3' that's playing silly b***'rs. There's a whole load of wiring on the NS behind the headlight, but I've not got a scooby what any of it's for.

Attached is the wiring diag from the BoL, 405D, OWM 3198, but I could do with some help working out how to read it. I've always regarded such things as a bit of a 'black art' but it looks like its about time I de-mystified such things!

The only sender I'm aware of is the one on the 'stat housing, just ahead of the fuel filter, there's two there, one for the AC, which I removed some while back; and the temp sender. I believe some 405's have a sender in the OS (vertical) tank of the rad, I'm fairly sure my red one (that was a non-AC car, on a 'L') did; but on this one its blanked.

Mine's a twin fan with 3 Relays: just looked back through the 'Accident' photos of 2014, fan wise, both panels were identical, surprising really as the donor car which provided the new front panel was non-AC (I'd previously thought that non-AC cars were single fan), hence it was impossible to refit the condenser due to a central mullion being in the way of doing so.

I've got all the info on the donor car, including reg & VIN, if needed.

[Paul-R]

One thing I would check is to make sure that there is no air in the system. When the engine is warm and the system pressurised crack open the bleed valves a little and see if any air comes out before the coolant does.

[white exec]

If you have no thermo switch fitted to the rad (usually screw-in, 3-wire), then the circuit diagram above isn't the right one . . . it's for the older thermo sw + 3 relays, as used on BX etc etc.

If you can post your VIN number, I'm sure someone will be able to help with a possibly more helpful diagram.

Meanwhile, even the later ECU controlled twin-fan systems, with or without AC, use the three relay set-up to achieve Hi and Lo speed for the fans.

Down front, you should find a row of these three relays, 1" cube jobbies, usually black. Sited here, they suffer from wet and contact corrosion. Unplug each one (they are identical relays) and clean up the external blade contacts back to bright metal, and try to clean the relay socket contacts as well. A small piece of thin glass-paper, emery paper, or a thin nail file/board, plus some contact cleaner, will help.

If you're feeling confident, you can open up the relays (ping the outer plastic case off) and check the contacts are clean/not burnt. They're each a standard automotive 12v 30/40A changeover relay, readily available. If these three interconnected relays do not function properly, fan mayhem usually results. Your fault may lie elsewhere though, but worth eliminating these.

[Pug_XUD_KeenAmateur]

Thanks Chris and Exec, both really simple checks I shall be doing either later or tomorrow. Am mindful of the urgency, coz should I have an airlock, my HG is in peril !

Am familiar with the location of the relays and certainly the right time of year for damp issues (which was the cause of the NS Horn having packing up, changed while doing the headlights recently). Think I'll pass on opening 'em up, coz I must have a spare set anyway from the old accident damaged panel.

My vehicle VIN is VF3**************[VIN obfuscated, can be read by forum staff]
Date of first reg'n Dec 1995 on an 'N'

Panel vehicle VIN is VF3**************[VIN obfuscated, can be read by forum staff], reg L792 GJO, scrapped 2014

[Pug_XUD_KeenAmateur]

looks like its turned out a simple one in the end, traced it to dirty connections on the Sender atop the stat housing, did take a close up photo of the very un-pretty state the pins were in, but blurred so useless. Another of those occasions where I was glad of me little model-maker's miniature rotary wire brush (at £1 ish for 10 or so, they're worth having in the toolbox and last better in use than you might expect).

Seems that the system to the fans is designed to 'fail-safe' if the sender fails. I took this pic of the fans running on fast having removed the feed to the sender (you can see it atop the fuel filter, its brown) and turned the ignition on.

Simples! Makes a change!

NB1: anyone know how the connection comes out of the bottom of the Relays? They look dry but I haven't been able to check em properly as its far from obvious how to unplug 'em. As yet, I've not dug out my spares, which are probably in the loft.

NB2: anyone found a way to open the bleed on the bypass hose without breaking it? Mine's the later plastic type, implying that the hose has been replaced at some point in the past, and it don't wanna open, I've twisted it as much as I dare. The 405 has only the one bleed: this was rectified on the 406 with a bleed on the heater hoses, but not so on mine. I do have a brand new hose in the loft, but if I can get this one to function so much the better, thankfully no reason to suspect air in the system, hoses uniformly warm and heater functioning as it should.

[white exec]

The fan relays are each 5-pin, and are usually plugged into a 5-pin relay socket, from which the four (or five) cables take off. If the relays pins/blades get corroded, it can be difficult to unplug the relay from the socket. Give the small gap between relay and socket a generous squirt of WD40 (or better, contact cleaner) let it work in, and lever the relay and socket apart, evenly on all four sides. It should reconnect much, much easier!

Good news on finding the dodgy sensor connection. I had forgotten that the system is designed to fail safe - yours did sound rather erratic though.

[white exec]

I've just taken another look at your excellent "turbo propelled" photo . . . Enough gust there to drive the car!

If those are the three relays, in their plastic bags, what an awful location for them - guaranteed to get the full dose of weather, spray, salt... and bagged up to keep the moisture there! On XM, the same three are lined up together, tucked under the front slam panel: still not a great place, but at least they get the heat from the engine to dry them out afterwards! (They're can corrode on XM, too.)

[Pug_XUD_KeenAmateur]

yes indeed, and as cars go it's light, about 1100Kg, Location really could be better couldn't it, grille removed of course, but nonetheless.....

do you think we can put that one down the bean counters, whom were no doubt keen to minimise the amount of wire involved? Its chunky stuff to these

[ekjdm14]

Ugh plastic bags round electrics... The first "mod" my dad made to his 309 on purchase, was to cut the water filled sandwich wrapper off the distributor cap...

If this is a similar setup to the X1 Xantia then, as you've found, the cooling fans do default to "on" in the event of sensor failure/disconnection. I found this myself when I got the engine freed up and cranked it sans-head, they only seemed to switch on once the engine had been cranked though & then stayed on. Before it's cranked they stayed off.

[white exec]

On a good few cars, there's an "Engine running relay", which only powers up when the engine runs (i.e. when the alternator produces output). This relay allows things like AC, HRW, heated seats, etc to operate, which otherwise would consume a lot of current without alternator supply. Possible that cooling fans come into this category on some models, although on others they don't.

Common, too, for many electrical items to extinguish when cranking is done, to maximise available current for the starter motor (and glowplugs, if diesel). Again, cooling fans may switch off while cranking.

[Pug_XUD_KeenAmateur]

they only seemed to switch on once the engine had been cranked though & then stayed on. Before it's cranked they stayed off.

yes, this was the case with mine too, the key was out when I removed the connection to the sender, then having put the key in & turned it towards aux they cut in immediately. Switching it off again then had no effect.

My first Pug was a 309, a 1987 Series 1 GRD 1.9na, with cam mounted PAS pump... which strangely, was deleted on the equivalent Series 2. Happy memories.

[ekjdm14]

Yes happy memories for me too, of long summers with actual sun, hearing England go out of Euro '96 on the Clarion stereo sticks forever in my mind & the chill down my spine when 3 lions came on the radio with the updated commentary clips... (I've since grown to hate professional football lol)

That was a 1988 registered S1 GR, 1.6 petrol in Silver Bronze. IIRC the distributor was driven off the cam end on that one. Manual choke was better than wax-stat auto chokes of the era too. I think that was the beginning of my love of French cars