Overheating

[Batfink 201]

My 205 gentry is getting too warm.

The warning lights are coming on.

 

What could be wrong - the car has managed a 500mile journey to Newcastle and back without a hitch but driving to castle coombe it overheated along the motorway

 

The radiator is hot too touch, the oil and water look uncontaminated.....

 

Going to do a compression check tomorrow but fingers crossed that should be ok - cars only done 75,000miles!

 

Pressure cap? or something worse?

[hengti 2]

it's always a brush off whenever people say this, but try the search facility - there are loads of threads about o'heating - should be able to assemble a list of suspects pretty quickly

 

my initial suggestion would be the the fan - is it cutting in?

 

 

 

searchsearchsearch!

[Batfink 201]

fan is irrelivant once a car is moving at a decent speed

[Batfink 201]

ok done a search!

thermostat - can't be this cos radiator is hot? If thermostat was stuck off the radiator would be cold? maybe partially open?

 

can you remove a themostat and test it with a multimeter?

 

Water pump - how can I test it!

Edited March 25, 2006 by Batfink

[hengti 2]

good point re fan - apols!

 

not sure how you'd go about testing 'stat with a multimeter

take it out, boil up the kettle - pour some in a saucepan - chuck your 'stat in along with a thermometer - check it opens when it should (rating is stamped on bottom of stat)

 

you should be able to check that your water pump is working by ensuring that there is a flow of water being returned to the expansion tank via the hose at the top of it

[Guest BrainFluid]

Hey Batfink,

 

Like Hengti says, whipping it out and testing in a pan of water will clear up any any doubt. If you drop it into a pan of water of the specified temp (hard to get, better off just dropping it into a pan of near boiling) and just look at it and see if it moves or not. This is quite a fun test, it marvellous how it works open.

 

I dont know if you have a Haynes manual or not so I might as well write down all the possibles from it for you.

 

Overheating;

 

Insufficant coolant in system.

Thermostat faulty.

Radiator core blocked, or grille restricted.

Electric cooling fan or thermo switch fauly.

Ignition timing incorrect/ ignition system fault.

Inaccurate temperature sending gauge unit.

Airlock in cooling system.

 

 

Can you belive that it doesnt even mention the collant pump! Crazy god darn fools! So, added to the list;

 

Faulty water pump

And I would also add is there enough coolant in the coolant, lol, if your coolant is mainly water and hasnt got enough er, coolant in it then this can be the cause but unlikey seen as were in the cold months. Unless it was a really warm day where you are?

 

Well thats all that I can help. Good luck! Dont run the car any more than you have too. Too much heat to often and you risk blowing the head gasket at best. At worst you'll sieze the engine.

 

Nate.

 

And if you knew all this anyway. ah well

Edited March 26, 2006 by BrainFluid

[jonD6B 0]

I would just replace the thermostat anyway regardless, they're only a few quid and takes 5mins to change. I personally would also back flush the system and add 'water wetter' to stop the water from foaming when at full temp. it has reduced my water temp by almost 10 degrees. Good stuff for a tenner. This is obviously after you have checked for leaks.

[jonah 1]

Faulty water pump

And I would also add is there enough coolant in the coolant, lol, if your coolant is mainly water and hasnt got enough er, coolant in it then this can be the cause

 

Doubt it's the water pump... what is there to go wrong with it? Unless the impellor fell off the shaft? But then there would be no flow at all, so the radiator wouldn't be hot.

 

It won't be too little antifreeze in the coolant either, antifreeze is actually less effective than water as a coolant, which is why you shouldn't put too high a concentration in (only enough to prevent freezing and corrosion).

[Rob_the_Sparky 9]

Just cause the rad is hot to touch doesn't mean that you are getting enough water through it by the way. Much above 60C and you won't be able to touch it...

 

Rob

[Batfink 201]

ok

I ran the car and the top of the radiator was too hot to touch though the bottom was cool

took out the themostat and stuck it in water boiled from the kettle

It opened about half a centimetre

[Guest BrainFluid]

It won't be too little antifreeze in the coolant either, antifreeze is actually less effective than water as a coolant, which is why you shouldn't put too high a concentration in (only enough to prevent freezing and corrosion).

 

 

Is that true? I thought that it helped to keep the coolant cooler? It certainly increases the boiling temp of water anyways. But hey if I'm wrong I'm wrong!

 

 

Looks like your thermostat is working though Batfink, though hard to tell what temp it is actually opening at...And to be honest I dont know how much it should open either!

 

The only other thing that I can think of is wether your oil needs changing. Old oil can lead to over heating can it not?

 

Nate.

[hengti 2]

ok

I ran the car and the top of the radiator was too hot to touch though the bottom was cool

took out the themostat and stuck it in water boiled from the kettle

It opened about half a centimetre

 

 

you likely need a new rad mate

 

sounds as though it's corroded/sludged internally and isn't allowing proper circulation

 

they're relatively cheap though (£40ish from gsf/eurocarparts) and aren't too difficult to fit

 

as an interim measure, you could try flushing it through to see if that helps

[Batfink 201]

yeah im not sure how much the thermostat should open to be honest

Water has a higher boiling point than if you add coolant to it. Coolant stops corrosion and frothing though

 

Oil temperature has been normal so I dont think its that

 

Could it be the themostat is not opening fully so the bottom of the radiator stays cool?

I guess I could try running the car without the themostat to test that theory

 

you likely need a new rad mate

 

sounds as though it's corroded/sludged internally and isn't allowing proper circulation

 

they're relatively cheap though (£40ish from gsf/eurocarparts) and aren't too difficult to fit

 

as an interim measure, you could try flushing it through to see if that helps

 

I've got a few spare so I'll try one of those

[simonb 0]

Is that true? I thought that it helped to keep the coolant cooler? It certainly increases the boiling temp of water anyways. But hey if I'm wrong I'm wrong!

Looks like your thermostat is working though Batfink, though hard to tell what temp it is actually opening at...And to be honest I dont know how much it should open either!

 

The only other thing that I can think of is wether your oil needs changing. Old oil can lead to over heating can it not?

 

Nate.

 

I run a fairly concentrated mix (about 70% coolant) and have no problems with overheating. The temp sits between the 3rd and 4th line on the guage all the time. I'm sure that using a more concentrated mix is better for protecting the internals as this should reduce corrosion down to a minimum.

[Guest BrainFluid]

I run a fairly concentrated mix (about 70% coolant) and have no problems with overheating. The temp sits between the 3rd and 4th line on the guage all the time. I'm sure that using a more concentrated mix is better for protecting the internals as this should reduce corrosion down to a minimum.

 

 

 

Sorry, I didnt mean about the corrosion side of things, I should have just quoted the bit about water being better than water with coolant (aka antifreeze) at keeping the temp down...

 

I could have sworn that it helped to keep the coolant cooler than just water alone.

 

Nate.

[ashley peddle 3]

I run a fairly concentrated mix (about 70% coolant) and have no problems with overheating. The temp sits between the 3rd and 4th line on the guage all the time. I'm sure that using a more concentrated mix is better for protecting the internals as this should reduce corrosion down to a minimum.

 

Isnt that a little high? mine sits on the 2nd line of the guage (half way between 2nd and 3rd when doing town driving) but never gets above the 3rd line (because of the fans)

[Veero 1]

Mines historically run slap bang in the middle of the gauge usually just above 3rd marker but often just below 4th. Nothing too warm, steady on motorway driving and dropping slightly on coasting but can quickly rise in traffic which is always reversed after moving say 100 yards or so.

 

Last monday a hose popped and I think the thermostat died and my heater stopped working, so replaced hose and thermostat on Saturday, ran it up to temp, bled it again, heater works fine but now when running it warms up quickly and sits just below where it is in this pic:

 

 

Even coasting down a hill in neutral it won't get lower than that. Now the the thermostat I bought was from GSF (renowned for supplying wrong parts? or so Ive heard) and it is definately on average hotter than it ever has been. It doesn't actually overheat but climbs to just below the 5th mark when the fans kick in and bring it down to halfway between 4th and 5th marks. As far as I can tell there are no blockages, although rad is hot I wouldn't say its anywhere close to 89 degrees. This leads me to think it is not opening at a low enough temp and circulating to the rad since the heater matrix hoses get hot much before the top rad hose does.

 

Now I have searched about this and found there to be several thermostats. The OE reference for mine (phase 2 1.6) is 133844 which according to ECP is the correct one, rated at 89 degrees. They do stock another 82 degree one and since it's only a few quid Im keen just to try it tonight and see since Im a bit concerned about running it this warm.

 

Any ideas? Could I have a knackered temp sensor or shall I just say sod it and try the 82 degree one?

 

Also does anyone have the actual temperatures that the incriments represent? I remember seeing a French dial with the temps marked on it.

 

Veero

[tom_m 0]

the fifth line on the gauge (the one your needle is just about pointing at) is 90 degrees c. as long as it doesn't go over this its fine.

 

mine runs at the 4th line when moving and i don't let it go over the fifth line in traffic (manual fan) the standard gti temp switch should bring the first stage of the fan on around there (89-92 degrees ish), and keep it steady unless its way hot. the full speed comes on at around 100-110 degress iirc and should get the temp down pretty quick unless you have something seriously wrong with your cooling system

 

A search should clarify the correct temps for the rad fan switches i know anthony has posted them in response to a quirey i made. there are several different temp switches that will fit from the model range.

Edited March 28, 2006 by tom_m

[jonah 1]

Sorry, I didnt mean about the corrosion side of things, I should have just quoted the bit about water being better than water with coolant (aka antifreeze) at keeping the temp down...

 

I could have sworn that it helped to keep the coolant cooler than just water alone.

 

Not sure about boiling point, but even pure water will not boil until over 100 degrees in a pressurised cooling system, so that shouldn't be an issue when the 'stat is rated at 82 deg.

 

The reason I said water is the better coolant is that (according to some figures I found on the web) antifreeze has a lower Thermal Conductivity and a lower Specific Heat Capacity than water. So it will be less effective at absorbing heat from the engine internals and transporting it to the rad. It also seems thicker (more viscous) so I'd expect it to reduce flow rates through the system slightly as you increase the concentration. So I just run the minimum recommended concentration to prevent corrosion and freezing.

 

Also once did most of a rally with only water in the system after an emergency repair to a burst hose that had lost all the coolant - didn't have any further problems with overheating there despite working the engine very hard.

[Guest BrainFluid]

Hmm, intersting stuff huh!

 

I've done a search too and it looks like your right from what the web is saying I stand corrected!

 

My temp gauge always used to sit on the first line of the gauge unless I'm in traffic but now that Ive fitted the extra coolant heated fuel filter for the veg oil it never even reaches the first mark! Unless in traffic of course. ( Turbo Diesel)

 

The down side of this is that the heater gives of very little heat now even less than it used too, which wasnt very much, but after reading all this I think that I had better check that my thermostat is'nt stuck open. Just in case!

 

Thinging about it I'm surprised that there isnt more mods outs there to help cool your coolant further, extra little rads and the like. Suppose it would all be a bit fiddily really but low temps is one of the prime things to keep your engine in good condition is it not...

 

Nate.

[Batfink 201]

a cold engine is bad too - you can cool an engine too much and the oil does not lubricate enough

[markic 0]

70% is far far too high a concentration. Anti-freeze is EXACTLY what it says on the tin! ANTI-FREEZE. Some dearer types do have ADDED corrosion inhibiters, but all bog standard anti-freeze does is stop the water in the cooling system from freezing, the internals of the water jacket etc will be no more corroded with a 30% mix(by far enough protection in this country), than they will off a 70% mix. The only sure way of stopping the internals corroding would be to remove the oxygen from the water, but then it wouldn't be water anymore just hydrogen.

Water is the best liquid conductor of heat. thats why it has been used all this time.