406 1.8 16V coolant temp, uphill climb with A/C on

[LFY]

Hello dear members!

I need some info regarding my car's normal operating temperature when going steep uphill with A/C on in hot summer days.

I have the following problem:

There is a road near where i live. It is very steep uphill for about 5 kms. In summer when outside temperature reaches 40 °C, if i drive uphill in that road with A/C on my coolant temperature reaches about 100 °C! and keeps staying at 100 until the inclination decreases a bit and it starts to cool down. (my speed is near 60 - 70 km/h).

If i increase my speed over 80 km/h, the engine temperature goes down below 100 °C. (reaches about 90 - 93 °C)

Is it normal for my car to behave like this in the above-mentioned situation?

I'm worried about engine damage when it reaches 100 °C.

My car is a 406 1.8 16V (XU7JP4 engine).

What about your cars? Do they behave the same way in those situations?

[jimmymarsbar]

If you're doing that speed on a very steep hill, I'd expect the engine to be revving at quite a rate, regardless of outside air temperature etc.

Factoring in the air temp, as well as the work the car has to do to power the A/C unit, as well as anything else going on in the car (lights, stereo etc), it's probably fair to say that the engine coolant temp will be fairly high.

When topping up the coolant, pay attention to the mix ratios and optimum operating temperature ranges on the bottle - a 30/70% coolant/water mix won't have as broad a range as a 50/50 mix

[LFY]

Thanks for your answer Mr. jimmymarsbar

There is high quality pre-mixed 50/50 coolant in my car and there are no air bubbles in the system.

If you're doing that speed on a very steep hill, I'd expect the engine to be revving at quite a rate, regardless of outside air temperature etc.

At those speeds my engine turns around 3000 - 3300 rpms.

Factoring in the air temp, as well as the work the car has to do to power the A/C unit, as well as anything else going on in the car (lights, stereo etc), it's probably fair to say that the engine coolant temp will be fairly high.

So, you want to say that reaching 100 °C in those situations considered normal? (or higher than normal?)


I should also add that with A/C off, my fans kick in @ 97 °C and turn off @ 92 °C .

[Goc3k]

When topping up the coolant, pay attention to the mix ratios and optimum operating temperature ranges on the bottle - a 30/70% coolant/water mix won't have as broad a range as a 50/50 mix

I don't know about super modern coolants, but the older polypropylene / ethylene glycol based coolants are actually much less efficient at transferring heat than pure water (i.e, distilled / de-ionized water is near pure). Specific coolants for specific engines contain the required rust / corrosion inhibitors than keep the system in good shape, these break down over time hence the need to change the coolant, and hence most manufacturers recommend a coolant and the minimum amount you should use. During the winter time it also helps with its namesake of anti-freeze as well, of course.

Chances are more likely your cooling system has near or over two decades of silt and corrosion built up in it, and that the radiator has lost more than a few fins to stone damage (if it's original) - this might be worth looking in to first if you are concerned about overheating, no idea if much damage is really done running the engine for a few minutes a little hot though.

Hope that helps!

[LFY]

Chances are more likely your cooling system has near or over two decades of silt and corrosion built up in it, and that the radiator has lost more than a few fins to stone damage (if it's original) - this might be worth looking in to first if you are concerned about overheating, no idea if much damage is really done running the engine for a few minutes a little hot though.

Thanks for your answer.

My cooling system seems to be ok.

I think my fans don't go into high speed mode enough when i turn A/C on. Most of the time fans operate in low speed mode. (My A/C pressure switch is not faulty)

I checked my radiator at different spots and they were all hot and had the same temperature which means that coolant is circulating well.

My car never overheats! It just reaches near 100 °C in those particular situations.

Some people told me that it is completely normal for a 406 1.8 16V to reach 100 °C with A/C on when uphill climbing.

They told me that there is no need to worry about anything!

Are they right?

[Goc3k]

Radiators do still become less effective over time even if all the cores appear to be working fine - the outlet area of the radiator should be noticeably cooler than the top inlet area. Another easy check is if you have loads of old debris and leaves / rubbish clogging all the fins in the A/C condenser (every one I even pull out is full of rubbish!), which would reduce airflow through it to your cars radiator, just have a look through your front grille with a torch and see if it looks okay. Don't try pressure washing it or anything though.

The extra fan operation when A/C is on is mostly to stop the A/C condenser from becoming heat soaked - as it's right next to the hot radiator. if the A/C blows cold all the time then you know the fans are operating as they should, so that's fine. Remember also at speeds above 70 km/h the speed of the air flow past the engine is much greater than what kind of air flow the fans can manage.

Certainly take nothing you read off the internet as the whole truth, but I'd say nearing 100c uphill over a fair distance at speed in such high ambient air temperatures is to be expected, and is probably nothing to worry about.

[LFY]

Dear Mr. Goc3k,

Radiators do still become less effective over time even if all the cores appear to be working fine - the outlet area of the radiator should be noticeably cooler than the top inlet area. Another easy check is if you have loads of old debris and leaves / rubbish clogging all the fins in the A/C condenser (every one I even pull out is full of rubbish!), which would reduce airflow through it to your cars radiator, just have a look through your front grille with a torch and see if it looks okay. Don't try pressure washing it or anything though.

I have checked my radiator and condenser before and they were all clean with just very little leaves between them which i cleaned.

So, you think i should replace my radiator because it is 12 years old even if it seems to function properly.

The extra fan operation when A/C is on is mostly to stop the A/C condenser from becoming heat soaked - as it's right next to the hot radiator. if the A/C blows cold all the time then you know the fans are operating as they should, so that's fine. Remember also at speeds above 70 km/h the speed of the air flow past the engine is much greater than what kind of air flow the fans can manage.

As i told previously, if i increase my speed over 70 km/h, the coolant temperature decreases and reaches about 90c at around 100 km/h in that steep uphill with A/C on.
When i turn A/C on, my fans operate in LOW SPEED MODE. I think they should go into HIGH SPEED MODE more in order to prevent coolant temp to reach 100c. I also noticed that my friend's 406 fans went into HIGH SPEED MODE more than my car when he turned A/C on.

Yes, my A/C blows cold all the time.

Certainly take nothing you read off the internet as the whole truth, but I'd say nearing 100c uphill over a fair distance at speed in such high ambient air temperatures is to be expected, and is probably nothing to worry about.

Yes, maybe nothing to worry about but i think the maximum coolant temp with A/C off should be the same with A/C on.

There should be no more than 1 - 2c difference in temperature between them.

[Goc3k]

12 years is not too old, I suspected you might have an older 406 with an original - would still be a good idea to check inside the cores if you are able to take it out though (if you want to pursue the problem) - you can peer through the inlet / outlet ports where the hoses connect once drained to see how scaled up the insides are.

As i told previously, if i increase my speed over 70 km/h, the coolant temperature decreases and reaches about 90c at around 100 km/h in that steep uphill with A/C on.
When i turn A/C on, my fans operate in LOW SPEED MODE. I think they should go into HIGH SPEED MODE more in order to prevent coolant temp to reach 100c. I also noticed that my friend's 406 fans went into HIGH SPEED MODE more than my car when he turned A/C on.

I'm not familiar with the 406, most cars as a general rule will have one fan dedicated to cooling the AC condensor and one fan for the engine radiator - I think they're just one big unit on the 406 though?

Check the fan switch to make sure it will engage high speed mode on both fans if you think that is an issue. Not sure how easy it is to get out of the 1.8, i assume not too bad. You can use a water bath (freshly boiled kettle over it into a teacup for example, or use an old shallow thermos flask - though this can be a bit tricky). A 95C+ electric heatgun would be great, if you have it. Don't use a blowtorch or lighter as tempting as it is.

You are right about maximum temperature change. Does the car also reach nearly 100 when the AC is off going up the hill? or only when the AC is on?

[LFY]

Thanks a lot for your help Mr. Goc3k,
You are a very professional man!

Check the fan switch to make sure it will engage high speed mode on both fans if you think that is an issue. Not sure how easy it is to get out of the 1.8, i assume not too bad. You can use a water bath (freshly boiled kettle over it into a teacup for example, or use an old shallow thermos flask - though this can be a bit tricky). A 95C+ electric heatgun would be great, if you have it. Don't use a blowtorch or lighter as tempting as it is.

I had tested them before and they seemed to work fine.

My car has two fans in front of A/C condenser and they both turns whether in low speed mode or high speed mode.

You are right about maximum temperature change. Does the car also reach nearly 100 when the AC is off going up the hill? or only when the AC is on?

With A/C off, the temp is completely normal and it never exceeds 95c under any circumstances (even very steep uphill - full load) and it is worth mentioning that with A/C off, LOW SPEED MODE is enough to cool the engine in all situations and there is no need for HIGH SPEED MODE.

With A/C off my low speed fans turn on @ 95c and turn off @ 92c and if i drive at speeds more than 60 km/h, fans never turn on and temperatures reaches the lower minimum (which is the temp when thermostat closes and coolant circulation stops).

I examined my A/C refrigerant pressure switch and found something interesting!

As you know, this switch is responsible for determining if the fans should go into LOW SPEED MODE or HIGH SPEED MODE when A/C is on.

There are 3 different pressures written in the switch. The last one refers to the pressure needed for fans to go into HIGH SPEED MODE.

This is my car's A/C pressure switch:



The refrigerant pressure needs to reach 32 BAR in order for fans to go into HIGH SPEED MODE.


I searched the market and found out that the original PSA switch has different pressures written in it.

This is the one i found (look at pressures):




This is also another one:






If you compare pressures, it will be:

2.3 - 18 - 32 (My car)

2.5 - 17 - 26 (Bitron Switch)

2.0 - 17 - 26 (Roster Switch)


So, that means if i change my pressure switch, my fans will go into HIGH SPEED MODE more than before because refrigerant pressure reaches 26 BAR sooner than 32 BAR and if my fans go into that mode sooner (or more) then my coolant temperature also decreases with A/C on.

Could it be my problem? What do you think?

[Hell Razor5543]

I wonder why you have an 'over pressure' switch? 6BAR is 90psi.

[LFY]

I wonder why you have an 'over pressure' switch? 6BAR is 90psi.

My switch is aftermarket which probably had been replaced by the previous owner of the car.

So, you think if i replace my switch with Bitron one, my fans go into HIGH SPEED MODE sooner and more?

[Hell Razor5543]

On that I cannot answer. However, unless there is a proven reason as to why a higher pressure switch should be fitted, I personally would go back to factory specifications.

[Goc3k]

Fan operation does seem to be the issue. It seems at face value that changing to lower value pressure switch should solve the problem (or at least narrow down the issue potentially) - I would think since they're just switches that you could chop and change between them without issue.

You would have to get the system properly drained and re-gassed if you want to take that pressure switch off though by the looks of things. Then you've wasted 50 quid on draining and gassing alone before buying the new switch.

If you can be bothered, I'd unplug the switch entirely and wire the ac fan so high speed mode is engaged permanently (achieve this at the plug or the ac fan motor directly, whatever is easiest). Then go for a drive under the conditions that cause the temperature to creep up - if the problem is solved, then great, get a lower pressure switch and install it. If the problem persists even with high speed mode on all the time, then you haven't wasted any money on a new switch & gas, and have crossed fan operation off of the list of "possible" problems.

Another option if you have a shed full of odds and ends to work with would be to spur a little bulb off of the high speed mode circuit, then you know if there is current flowing and possibly the motor itself is at fault. (If that could be the problem, anyway)

Hope those are some useful thoughts! Been a bit warm here the last few days and i've been having mild regrets about ripping the AC from my car. haha

[LFY]

Thanks again Mr. Goc3k,

If you can be bothered, I'd unplug the switch entirely and wire the ac fan so high speed mode is engaged permanently (achieve this at the plug or the ac fan motor directly, whatever is easiest). Then go for a drive under the conditions that cause the temperature to creep up - if the problem is solved, then great, get a lower pressure switch and install it. If the problem persists even with high speed mode on all the time, then you haven't wasted any money on a new switch & gas, and have crossed fan operation off of the list of "possible" problems.

I have tested something like that before. One of my friends unplugged the A/C pressure switch and put a wire between it's socket and the sensor terminals.

By doing this, whenever compressor engaged, fans went into high speed mode and whenever compressor disengaged fans turned off.

It did NOT make fans to run in high speed mode PERMANENTLY but ONLY WHEN A/C compressor engaged.

When he did this to my car, my problem solved and at those hard conditions mentioned my temperature reached about 94c and didn't go higher than that.

But i removed that wire because i thought that it may be harmful for the system to work this way and when i removed it, the problem started again and temp reaches about 100c again! (and my fans don't go into high speed mode any more)

If i wanted to makes fans run in high speed mode PERMANENTLY, i could do something very easy! If i unplug the coolant temperature sensor socket (the brown one), fans will go into high speed mode permanently.

[Goc3k]

Sounds like a safe enough gamble to me to go ahead and swap on a different, lower bar pressure switch. Would seem likely someone in the past has put the wrong switch on out of error / cheapness, not sure if you could confirm this with the VIN and a parts manual?

Let us know how it goes if you decide on the swap!