306 Temperate suddenly all over the place

[leadfootlydon]

My London runaround is a 306 (1.8 petrol GLX). Had it two years and love it.

Recently I noticed the temperature was up in the 90s. It has never done that before, usually being rock-solid in the mid-80s. When stopped in traffic, the temperature even got as high as 100. Making progress, the temperature sometimes drops back to below 80.

What temperature does anyone else's 306 run at?

Why would mine suddenly go 'unstable' like that?

P.S. The TVR and Stag have always had bonkers temperature gauges, but the 306 is supposed to be our sensible car.

[trickywoo]

Dose the fan cut in? The sender unit may have failed?

[350wedge]

I assume you've checked the level of coolant under the bonnet? If its low it will definatly send the temps up. Maybe check rad for leaks as well if its getting old.

If coolant hasnt been changed for a while might be worth draining the system and re-filling with some fresh coolant.

[leadfootlydon]

Thanks for the replies.

Yes, coolant and oil is all there.

Yes, the fans do come on at 100 degrees. But that seems a tad on the high side when the car has never previously got over about 85. The fans turn off when the temperature drops back to 90.

Maybe this is how it is supposed to work, but it seems very odd that I have had the car two years and it only started behaving this way after the cold weekend just gone.

[spdpug98]

It could be that the thermostat is on its way out

[leadfootlydon]

Am I right in thinking some candidates would be:

1. Thermostat (Only partially opening, preventing the radiator from cooling like it should)
2. Temperature sender (Indicating hotter than it actually is)
3. A/C control unit (mis-reading temperature sender and causing temperature gauge to show wrong and fans to come on)
4. Radiator (Partially blocked, reducing circulation at low revs and therefore not cooling properly)
5. Water pump (not working properly at low revs, reducing circulation and therefore not cooling properly)

I am trying to account for the symptom that the temperature varies a lot depending on whether I am driving (temp low) or stationary (temp high).

P.S. I really appreciate your help. Many thanks.

[combemarshal]

I'd go for the Thermostat first (and if you get it from halfords make sure the gasket is with it, mine had been robbed!!) My Xantia is normally at 80-90, but can get up to 100, 110 you should start to think about moving to Iceland!!!
Take yours out, boil a kettle and pop it in the hot water and see if it opens, incidentaly, did you know it is wax that makes it open!

[megamaniac]

Iwould have to agree with combemarshal,stat first then rad flush or rad.Water pumps usually only leak, unlike some rover's and honda's that fall apart.

[steve_d]

There is the remote possibility the pump blades have erroded. Not common but I have seen it in both alloy and plastic pump rotors.

Steve

[zelleyford]

deffantley go for the Thermostat. but go very easy on the bolts when you un do them as they have probley never been tuched and there is a small chance thay you may snap the stud off like i did wonce on a 3.0 Supra that i was working on, i thort it no 1 will eaver no any diffrent. "there are 2 others"..... it will be ok" week later it came back on the back of a flat bed. it had over heated and cooked the block.. oney cost my boss £2500 to fix it. hence im no longer work there any more . but a nother very good tip is make shour that you use some sort of sealent not just the little one that they give you. Il also serjust useing some wet and dry paper with a dab of WD40 to clean bouth sides.

let me no how you get on

[Rob_the_Sparky]

Pugs often have a two speed fan set-up, can't remember for sure but I think my 306 did. (most 205s and 309s do for sure)

If so then it is quite possible the high speed fan is working but not the low speed fan, which cuts in earlier. You'd have to check on your car what system you have but it sounds likely from what you describe.

Slow speed can fail due to the series resistor dying (used to make the fan run slowly) or the radiator mounted fan switch.

Rob

[leadfootlydon]

Thanks Sparky, that sounds entirely plausible.

I haven't touched it yet, and the symptoms have persisted. I am trusting that I am not doing too much damage by sometimes having the temperature get to 100.

I recently bought the haynes manual, so I'll take a close look for a slow-speed fan control mechanism.

[leadfootlydon]

Just to rule it out for my peace of mind, is there anything that would cause an engine to produce more heat that normal?

Say, for example, the timing suddenly went off, or a plug suddenly started to cause the spark in that cylinder to be too soon or too late? Or the injection system is not working properly and the mixture is too lean? (I could be talking rubbish here, do let me know).

I filled up with petrol recently, so I don't think the problem was caused by bad fuel.

The engine sounds OK and there does not seem to be any loss of power. It is just running hotter in traffic than it used to.

[Rob_the_Sparky]

If ignition timing is a way out or it is running lean then they will run hotter but it doesn't sound that likely.

[leadfootlydon]

In case anyone ever has the same problem, I now have a 'solution'.

The solution is to keep the Air Conditioning ON. Yes, ON.

With the A/C off, the engine temerature may go high, as per the original posting. With the A/C on (and set to whatever high or low cabin temperature I like), the engine temperature is a rock-solid 85-ish.

Something in the A/C circuitry is managing the engine temperature too. Turn the A/C off and you turn off the engine temperature management.

[megamaniac]

Check that both fans are working.
When you have the aircon on the bitron unit(mounted on the n/s inner wing behind the headlamp) makes the fans run at slow speed all the time .This is what is keeping the temperature constant now .
It could well be that the slow speed temperature control isn't working as i would have thought that the fans should cut in at slow speed around the 92-95 mark and the highspeed cut in around the 98-100 mark.

[leadfootlydon]

Thanks. I will take a close look at how the fans are behaving.

I know that when left to idle (with the A/C off) the temp runs in a cycle, gradually rising to about 100 and then suddenly dropping back to about 90 when the high speed kicks in.

[hifihigh]

Thats normal 306 behaviour i think. Mine is the same anyway (i have a 2.0 with aircon). When the a/c is off the thermostat will stabalise at about 80 when moving and go upto 'bout 107 in a traffic jam or something before 1 fan will come on to bring it back down. With ac on both fans are used and are controlled by a different unit i think (bitron?). There is something about it on this page;

http://www.306gti6.com/forum/showthread.php?id=453...