Overheating Peugeot 405 - David O
Well, not overheating exactly but still a problem.

I have an old Peugeot 405 1.6 GR manual that runs at its usual temperature when on the move but when stopped or at low speed (at the traffic lights, in a jam etc), the temperature gauge rises much more rapidly than normal. Within a minute or two, the fan cuts in and continues to do so constantly until the car is moving again, when it quickly returns to its normal temperature. This may not sound disastrous but is not standard behaviour for this car. I have changed the radiator (this cured a similar problem a number of years back, and it was a bit rotten), checked the thermostat and flushed the cooling system but the problem remains. The oil and water levels remain fairly constant and don?t appear to have mixed. I have now exhausted my limited mechanical abilities and would appreciate any suggestions before the problem gets worse.


David O
Re: Overheating Peugeot 405 - Ash Phillips
Is it a two speed fan and is the low speed working properly? At speed airflow cools the engine and everything is ok, but when you stop on tickover, if low speed not working then the engine gets a lot hotter until speed two kicks in. My BX did exactly this and it had blown this huge 1 Ohm resistor by the radiator which killed the low speed circuit. Maybe similar on your car what with BX/405 relationship.
Re: Overheating Peugeot 405 - Michael
David, I had a 405 1.6 manual (H plate) for 3 years as a company car in the early 90's. It had two controls for the fan. 1 switched the fan on for normal engine temperature control but the other was (i think) to switch the fan on/off at low speed and after the engine was switched off. The only time I knew there was a problem was when the car started to misfire when in long traffic jams. The other clue was that the fan did not run after the engine was switched off as it should do (apparently to cure the hot starting problem that they tend to suffer from). In summary, check the second fan unit is working and confirm that the fan continues to run for 5-10 minutes after the ignition is turned off. The unit was located on the inner wing, from memory - can't remember what it was called but I had 4 replaced in three years. I'll search the old paper work to see if I can find any more info.
Re: Overheating Peugeot 405 - Michael
David, having read Ash's post, I remember that it was a resistor that failed 4 times on mine.
Re: Overheating Peugeot 405 - Ash Phillips
They cost 20 quid a pop for a BX and they sell them by the boatload, used to check it every 6 months - if it's hot its prob. ok, if it looks like it's exploded and ruptured the cannister, time to get the wallet out.
Re: Overheating Peugeot 405 - mike harvey
This is a bit of a puzzler, as it's generally the opposite of what one would expect to happen, ie overheat when the engine is producing more power. I have a suspicion that the thermostat may be to blame, either because it is faulty itself, or that it cannot work properly because it is in an airlock. An air lock in the thermostat housing would be more likely when idling, as the water pump is only just 'paddling'. I was going to suggest the guage may be faulty, and telling you it is hot when it's not, but your fan comes on and that's a seperate system. Could be the dreaded headgasket of course, wet liners I think in those.
All the best
Re: Overheating Peugeot 405 - mike harvey
When I started replying I was the first. All the other suggestions are better than mine. Please ignore the last. If only I could type quicker!Mike
Re: Overheating Peugeot 405 - Dave N
If it has twin fans, they run in series to start with, both at 1/2 speed, if it carries on getting hotter, they both switch to run in parallel. If one fails, then neither run at 1/2 speed, and only one runs at full speed. I have found this numerous times on cars with A/C.
Re: Overheating Peugeot 405 - Andrew
I had a 405 td. Having towed a caravan home I noticed that the radiator was p......g its contents all over the drive. The matrix had sprung a leak. That had been caused by excess pressure due to excess heat in conjunction with weak Peugot radiators,. Come to think I had never heard the fans running. After a great deal of inspection I found that there are 3 relays to govern the 3 different fan speed combinations ( These are situated to the front of the fans at the top and requires the grill to be removed). There is a single thin red trigger wire to each relay which enter the loom at the bottom and are spliced. The joint had corroded in the loom and hence no trigger feed to the relays and no fans. I had not noticed a problem up until this time which is testament to the normally adequate cooling of the radiator.
Another problem I found was a common earth connection for all the gizzmos at the front. This requires the front bumper to be removed to gain acess. That was looking a bit suspect and reqired a bit of cleaning and oiling.
Is your antifreeze/inhibitor up to scratch? If not corrosion sediment could have caused a blockage in the engine block and it will require some serious 'backflushing'.
Re: Overheating Peugeot 405 - Andrew Ellison
I have a diesel 405 GLD this has the same problem in stationary traffic. It is also particulaly bad when towing a caravan. Unfortunately removing the front bumper just to change a couple of components seems a bit drastic.
Re: Overheating Peugeot 405 - Andrew
OK so leave it then. The front bumper has to be removed to check and maintain the earth connections for the fans. Its not the hardest job in the book. If your fans are not working as they should and the engine overheats then problems can occur with the cylinder head warping and the gasket blowing. The 1.9d engine is particularly prone to problems after being overheated. Prevention is better than cure!!
Thorough checks. - David Woollard
David and other replies,

Too busy to drop in on many threads at the moment but have a fair amount of experience with pug/cit cooling systems so will throw my thoughts into the ring.

The "problem" as described really only mirrors the correct operation of a cooling system, but perhaps towards the top end of an acceptable range. An older cooling system will often do this, as will an extra load or high external temperatures. If it is all controlled within the normal range (you didn't say it went to the red) of the temperature gauge why worry, or does it seem it may boil one day?

On a brisk trip with a heavy trailer the other day my TD Xantia exhibited just these symptoms you describe, I too was a little concerned and experimented with putting the heater and blower full on...this would take five degrees from the temp gauge in a couple of minutes! But at the end of the day the system was just doing its job.

Ash/Michael have good points about the twin or two speed fans, you do need to check this out and ensure what you should have actually works.

Dave N mentions the cars with A/C, if yours has this I think you will find the fan switch is tied into the A/C, and the sensor isn't in the radiator but at the top of the thermostat housing.

You say the radiator was replaced a while ago, with a new one? Often an older radiator will have a build up of small blockages that make it marginal under stress. A brand new one is usually needed but it is worth removing and flushing it..........in-situ flush can give a small improvement but I would remove if possible.

Also the thermostat has been checked, how? Is it worth fitting a new one? On the 1.6 (never mind looking at the other 405 engines) there are several different thermostats with a ten degree difference in opening temperature. You need to know your engine code to find the correct one.

Mike H has mentioned a very important issue with these systems....Air! It is really hard, unless you know these systems very well, to fill them and remove all the air. The problem is that the filler is often below the highest point of the system so you need a header tank arrangement about 300mm above the filler. Only with a carefully filled/bled system will you have correct operation.

For my Citroen Club colleagues I produced a method for this and I'll pop it on the reply below for those that are interested, save this being a monster post. It relates to a BX but the principles are the same.

Hope some of this helps,

Fill/bleed methods. - David Woollard
BX coolant fill/bleed method.
Posted by David Woollard on June 3, 2001, 4:38 am , in reply to "Re: Possible faults.

Years ago cooling systems were simple and filling them just meant pouring in cooolant to the rad and a few minutes running would self-bleed any small air residue. My 1970 diesel tractor is like this, big old radiator mounted higher than all the other waterways, no complicated narrow hose runs curving over the engine - no problems.

But like many other modern cars the BX can be a real problem to fill and bleed. Models with the cap on the radiator are the worse as there is almost no head of water when filling, even those with the expansion tank aren't much better.

So my method is......

First locate all the bleed points on your particular engine. These may include one on the radiator opposite the filler cap, two on the thermostat housing, one on the small hose that leaves the thermostat housing, one on the metal heater feed pipe just behind the camshaft cover, one on the heater hose just to the rear of the engine, one on a small hose running just behind the radiator. I do not want to be specific to a particular model/year as I have seen cars with odd combinations of the normal set-up, just carefully look for them all.
With the engine cool remove the filler cap and fabricate some sort of header tank that will give about an extra 300mm head of water. Mine is very simple. It is a large plastic funnel for filling up tractor fuel that has a nozzle about the same size as the filler hole and holds 3 litres of coolant. I cut the nozzle at a point so that the taper just goes into the radiator/expansion tank filler hole and a firm push will keep it wedged there. I have seen loads of other clever solutions to this with little tanks held on a stand and filler hoses that connect to a modified radiator cap boss, I used mine because it was lying about at the time and has worked OK for 7 years now.
Now top up the system with coolant and allow the funnel/header tank to fill about 2/3rds. Bleed each coolant bleed point in turn until bubble-free coolant is seen. Close them all firmly. Start the engine and allow it to run at a fast idle until the thermostat opens and the radiator becomes fully hot. During this period you should see loads of small bubbles appear in the funnel/header tank, and as the thermostat opens a huge amount of air often bubbles up. Now stop the engine and bleed each point in turn again. Use great care as the coolant will be scalding. Top up the funnel as needed during this to keep it about 2/3rds full at all times. Close all bleed points finally and re-start the engine. Allow it to run for up to another five minutes for all the remaining small air bubbles to bleed off. When you are happy stop the engine and remove the funnel. Put the radiator cap back on with the coolant still right to the top (ie overfilled by cold standards). Allow the car to cool completely then check the level and add/remove coolant as needed. Give the car two days normal use then check the level again when completely cold. Again add/remove to get the level spot on. Only now consider this an accurate level to monitor from.

Why is this bleeding crucial to the BX? Well the thermostat and coolant temperature warning sensors (and fan switch on P.405 A/C models) are in a position that is easily left air-locked if this procedure isn't properly carried out. And these do not work properly in air, only if the water is in contact with them. So it is possible after a water loss, and re-filling without bleeding, for the engine to go above the thermostat opening temperature without it allowing coolant to the radiator. Then because the temperature senders are also in the air lock they don't indicate a problem. Result engine cooks and the head gasket/head are damaged.
Many BX (diesel in particular) head gasket problems follow a simple loss of water incident after a few days. It is my belief this is often due to the problem of bleeding the system rather than the initial fault damaging the head.

Well hope that essay helps, come back guys with any arguments!

Re: Thorough checks. - David O
Thanks for all replies. I will check the resistor to the fan and endeavour to bleed the system properly.

For info, the car doesn't have aircon, has a single fan and the radiator was new (Euro Car Parts, less than half the price of Peugeot main dealer). I believe the thermostat is the correct rating for the engine.

David O
Re: Thorough checks. - Michael
David, et al, my money's on the resistor!!

Value my car