Why is it................

[I.Mupferit]

that all the tin tops I have owned in recent years maintain a very steady temperature reading once the engine has reached operating temperature and even stopped in heavy traffic in high ambient temperatures, the needle doesn't move.

 

Yet in all 7's I have driven, even with modern engines, the temperature goes up and down like a fiddlers elbow when you are at a standstill in traffic with the fan cutting in and out.

 

Just curious really.

 

Brent

 

2.3 DURATEC SV

R 417.39 😬

[Alex Wong1697456877]

I've wondered that too. My VW never wavered from 90 deg. Ever. Right up to when the turbo blew.

[Wingnonut]

My BMW doesn't even have a temperature gauge

 

W.Nut .

 

Rosso Superlight no.087

[Frying Pan]

Nor does my SportKa

 

See some pictures of the build here. 6000 miles completed!

[Shaun_E]

I'm pretty sure they aren't really connected to any coolant sensor at all but are just on a timing device that waits a while and then moves the needle to the desired point . This way nobody gets unduly worried about their engine (until like Alex's it blows up 😬)

 

A more serious answer I guess has to do with a few things:

1) The gauge is seriously overdamped to prevent any small fluctuations

2) Electronically controlled thermostats with careful management of coolant flow

3) Components designed to work together as a system

 

On a seven ony 1) might apply and if you have a decent gauge (e.g. Stack) then you can see the fluctuations clearly.

 

I don't understand how a correctly designed thermostatically controlled cooling system can allow an engine to be overcooled (referring to some of your previous posts on the matter). If the thermostat is shut then the engine coolant should reach the opening temp of that 'stat. If it doesn't then there must be a bypass that is allowing cool water into the engine. Once the stat opens then water will flow through the radiator until the temp drops below the 'stat closing temperature and so the cycle repeats. If the flow rates and radiator size are reasonably matched then the temp will slowly fluctuate between a range either side of the 'stat's opening temp - a well damped gauge would eliminate that fluctuation.

 

Yellow SL #32

[I.Mupferit]

I don't really understand how it can be overcooled either on a thermostatically controlled system and I don't think over damping of the gauge can be the answer as it surely needs to accurately reflect what is happening in the engine to avoid problems.

 

I remember on a 5 series BMW I had a few years ago, when the top rad connection came adrift, the needle moved pretty smartly upwards then.

 

I reckon it's your first explanation Shaun...........the timer ❗

 

Brent

 

2.3 DURATEC SV

R 417.39 😬

[Kevsta]

Don't know about that...my 944 (which has VDO guages) does fluctuate with the heat of the engine...I can watch it rise steadily in traffic and drop again when the fan cuts in. Worrying that some cars don't have them..then again, how many 'normal' drivers even look at them?!

[Shaun_E]

I think there is something wrong with the timer on my Seat's temp gauge - the needle goes to the middle position far too quickly. 😬 😬 😬

Actually this is a good point: my Seat is a 225bhp 1.8 Turbo as per the Audi TT and even on a really good thrash on a hot day the temperature doesn't budge from the normal position - that really can't be right.

 

Yellow SL #32

 

Edited by - Shaun_E on 20 Jun 2005 15:51:09

[LazerBrain]

My Golf GTi behaved like that - until the water pump failed. It then decided to test the upper end stop. The "get you home" mode of the ECU bypassed the turbo and disabled the aircon ☹️

 

 

cheers,

 

Darren.

 

Edited by - LazerBrain on 20 Jun 2005 16:09:08

[Bricol]

My old 1981 Renault 5 didn;t have a guage - it wasn't high enough up the options scale to get one.

 

Temp guage in the Cat when it has an operating sender to drive it, maintains a steady indicated 80 - regardless of fan or off - throughout the very hot Italy tour in 2003 it never budged.

 

Bri

[Colin Mill]

Ok let me try to get my mind around this "overcooled" thing. I think the problem occurs when the water flow rate is low (say at idle) and the rad has a good draft through it (fan on, lowish air temp) This means that the temperature of the water exiting the rad can be way below the engine temperature. Lets assume that the stat is shut and its being bathed in the bypass flow which (ignoring heaters!) is at the outflow temperature of the engine. As this rises the stat opens admitting stone cold water from the bottom of the rad. Because the stat does not respond instantly to the sudden drop in temperature the flow of cold stuff goes on for a spell and treats some selected bits of the engine to a big cooling off with the attendant thermal stressing. Presumably at some point the stat wakes up to the new situation and slams shut again and will stay that way till the bypass flow warms it back up again. We get cooling by instalments! Ok I have assumed that the stat opens quite sharply. If the stat has a more gradual opening over a temperature range than it might not oscillate. But if a system has enough loop

gain and sufficient phase lag (delay) it will oscillate.

 

From what I have so far gleaned from the revised Freelander cooling system the bypass has a much higher flow so when the stat opens the bypass water prevents the stat temperature dropping so violently.

 

Now if the water returned from the rad was not so cold the effect would also be reduced which is why I won't be fitting a fan thermo switch bypass in a rush. On the other hand putting the fan thermo switch in the bottom of the rad (with a suitably reduces operating point) might be a move in the right direction.

 

[MorganMan]

So far my SV 140 is very steady the temp climbs to around 80 and then stays there Early days yet.

 

I have read many of the posts concerning thermal shock and many of the explanations seem to assume that the thermostat operates like an on / off switch, ie either its closed or open, and on reaching its set temperature it snaps open turning on the flow from the rad big time. In reality it opens progressively as the wax expands heated by the bypass flow; cold water from the rad then blends then with the bypass until the thermostat settles to a balanced position. Where then is this dousing with cold water and thermal shock?

[I.Mupferit]

MorganMan, I agree with your hypothesis and I know the 'stat only opens and closes fairly gradually having witnessed this when testing them in a saucepan of water many aeons ago when I was having problems with a Lotus Cortina back in the 60's so I don't understand where the suddenness of the cooling comes from.

 

I do, however, know that it can be very sudden from having witnessed this very phenomenon on my current 7 with the Duratec 2.3. The gauge needle will steadily climb to around 85 deg c then when the 'stat opens will drop back to below 60 in about 3 seconds flat before slowly climbing back up. I can only imagine there is quite a high pressure from the pump which blasts the coolant round the waterways as soon as the 'stat cracks open. Maybe, even, the act of opening, itself, is assisted by the pressure from the water pump thus sending a slug of cool water coursing through the engine as soon as it is able.

 

Anyhow, I am working on a solution which involves an opposed blade damper blanking off the lower half of the rad and adjustable from the cockpit anywhere between fully open and fully closed.

 

But to get back to my original question, why doesn't the needle on my tintops creep up in traffic whereas every 7 I've driven including Ford and Rover powered variants always do?

 

Brent

 

2.3 DURATEC SV

R 417.39 😬

 

Edited by - BRENT CHISWICK on 20 Jun 2005 23:01:33

[MorganMan]

Brent, Its interesting that you see this on a Duratec as its the unusual position of the K series thermostat that is often fingered. With regard to the water pump, cooling system water pumps are impeller pumps they generate flow but not much pressure and the flow will be very restricted if, as we seem to agree, the thermostat has only just cracked open. Could it be to do with the position of the temp sender, I don't know where this is on a Duratec.

 

With regard to the original question, mine doesn't do this, it always seems to read a steady 80 - 82 degrees. I think some else got it right, the gauges on the tin tops are overdamped to give a steady reading.

 

Edited by - MorganMan on 20 Jun 2005 20:45:43 to correct spelling!

 

Another thought does the Duratec Thermostat blank off the by pass when open, this would reduce the blending effect. As I understand it the K series bypass remains open, therefore you have full by pass flow mixing with some cold as the thermostat cracks open.

 

 

 

Edited by - MorganMan on 20 Jun 2005 20:49:37

[Colin Mill]

Hi Brent

 

Interesting your thinking along those lines. I have contemplated if a servoed set of 'cowl flaps' over the rad would be a better solution than a water thermostat. Although this would in theory increase the warm up (as you would be heating the water in the rad during warm up the thermal capacity of the rad + its water must me only a small fraction of that of the engine itself.

 

I think part of the reason for the sudden effect of the stat opening is that it robs the bypass line of pressure drop and almost switches the flow from one route to the other.

 

Edited by - Colin Mill on 20 Jun 2005 20:55:52

[MorganMan]

Colin, the flow will take the line of least resistance, quick run around a full open bypass v long and tortuous route through rad followed by squeezing through a only just cracked thermostat? I'll take the bypass

[Colin Mill]

Hi MorganMan

Well, I'm not so sure. Against the extra length of the radiator route the bypass (at least on the K) is small. If the flow is viscous limited (I'm too lazy at the moment to work out the Reynolds No.) then the flow goes up as the 4th power of the pipe bore so the main route would win hands down. If the flow is inertially limited then it still goes as the bore squared.

[MorganMan]

Colin, I fully agree, but only if the main radiator route is fully open, but if the thermostat is just cracking open?

[Colin Mill]

Yes, it would be an interesting sum to work out how much the stat has to open before the two paths become equal. Somewhere I have a spare stat - if I find it I'll make some measurements

[I.Mupferit]

Hmmm, all fine and dandy except that the Raceline water rail setup doesn't employ a bypass...........of any sort. The layout utilises a water rail which channels the coolant from where it exits at the rear of the cylinder head to a position approximately 2/3rds towards the front of the engine where the thermostat is situated. The temperature sensor, however, is at the rear of the water rail and thus senses the actual temperature at the coolant exit from the head.

 

Now, Raceline have employed a similar setup on their installations for many years with the Zetec and one of the problems experienced initially, which I coincidentally discovered about the same time as others, is that the thermostat being remote and effectively acting as a valve stopping the coolant flow wasn't sensing the true temperature of the coolant in the cylinder head. This, obviously led to alarmingly high temperatures being seen on the gauge before, maybe due to convection, the message finally got through to the 'stat and it opened to allow a slug of coolant to flow from the rad thus suddenly reducing the temperature.

 

On my particular Zetec installation at the time, I was sufficiently concerned to immediately investigate the problem before using the car again and came up with the simple expedient of drilling a small hole in the 'stat base to allow some of the coolant to pass over the bulb and effectively keep it up to speed with what was happening in the cylinder head. After experimenting with hole sizes, I arrived at 2mm being the optimum which completely prevented the cycling effect and although the warm up period wasn't especially quick, it would get to 85 and pretty much stay there apart from my aforementioned observations when in traffic. 😬

 

I subsequently discovered, on discussing it with Raceline, that others had quite independently arrived at the same conclusion as me and it was adopted by them on all future installations. Now the Duratec runs with a pretty much identical setup and despite experimenting with hole sizes and alternative thermostats I just haven't been able to resolve the cycling problem. The only solution which appears to be doing the job is this damper I mentioned earlier albeit I can only, at the moment, adjust it from outside the car. ie with a long fine screwdriver through the grille. As I said, I am working on a better method of operating this damper which I hope to experiment with by the end of this week.

 

An interesting problem though which I hope to finally resolve soon.

 

 

 

Brent

 

2.3 DURATEC SV

R 417.39 😬

 

 

 

 

 

 

 

Edited by - BRENT CHISWICK on 21 Jun 2005 08:10:17

[MorganMan]

I don't like to question an installation by an organisation such as Raceline, but I don't like the idea of no bypass on a road car installation, and I'm not surprised that you see the effects that you do. The thermosat will start to open, but as flow starts it will then be hit with a slug of very hot coolant and the effect will be nearer the on/off switch effect. On a race car OK, but then why bother with the thermostat at all ?

 

Have you ever tried a small bore bypass, say 12 - 15mm from the thermostat housing to the bottom hose. This will give flow around the engine during warm up and control hot spots, it will bath the thermostat in engine temp coolant, smooth the opening and blend with the cold coolant from the rad in the bottom hose as the thermostat opens and flow from the rad begins in the bottom hose. If the Tee with the bottom hose is closer to the rad than the engine this will be all to the good as it will allow the bypass and botton hose flow to blend well before it hits the engine. With this set up I would eliminate the pilot hole in the thermostat as it will have the adverse effect of increasing the warm up period. (It would however help in bleeding the coolant system)

[I.Mupferit]

I know what you mean about a bypass and it is something I have considered installing. It was never really a problem on my old Zetec car once I had determined the optimum hole size and the engine didn't take too long to warm up, certainly it was by the time I was able to reach any blattable roads.

 

I really do think my rad is overcooling as even on a hot day with it half blanked off, I never see anything higher than 80 whilst on the move. My easy option, as I already have the adjustable damper is simply to refine the operation of that so I will play with it this week and revert to plan B if I can't resolve the issue with that.

 

My problem at the moment is with available playing time since I have so many things to do (non car related) before I need to use the car for 2 weeks on my French holiday.

 

Brent

 

2.3 DURATEC SV

R 417.39 😬

[I.Mupferit]

I have to report that my new cockpit adjustable radiator blind works brilliantly. 😬 Whilst sat in the 30 C temperatures yesterday waiting to get into Goodwood, the blind was half open and the temperature needle never went above 85.

 

This morning in much cooler conditons on the M25, I started off with the blind fully closed and left it like that all the way to Horton Kirby. The engine warmed up quickly and settled at just over 80 all the way without moving so I think I can call that a success.

 

Brent

 

2.3 DURATEC SV

R 417.39 😬

[SLR No.77]

It's obviously very easy to over-complicate the coolant temperature issue

 

My temperature gauge reads rock solid, and even in standing traffic does not exceed 90ºC - including a full hour in the scorching heat on the return trip from Le Mans (the French do road works also ). Also my gauge is the old VDO type - substantially less damped than the later "Caterham" versions. The key is not to improve the cooling but to locate the temperature sender in a position less affected by engine heat - it's not the engine that's heating up dramatically but the water rail to which the sender is attached - positioned directly over the exhaust manifold. Same applies to the temperature sender for the ECU. ie. engine temperature is fine but panic in the driver's seat 😬 When the car is stationary, the water rail heats up, when it is moving (or the fan is on) there is airflow over the manifold and the sender starts to read normal again.

 

Caterham know this is an issue and fit a modified sender setup to the race cars. Basically a small steel pipe around 4" long with provision to take both senders. This is fitted in the by-pass hose to the rear of the block (top heater hose is fine) away from the manifold. Not only will this give a correct (unaffected) gauge reading but it will also ensure the ECU is receiving the correct temperature signal. Speak to Caterham parts, it's only a few quid for the pipe and blanks for the old holes in the water rail.

 

Stu.

 

 

[stevefoster]

Not my VX Brent.

Rock solid in normal use. In the recent heatwave it rises by what I would gauge is 5 deg and then the fan cuts in and brings it down to 90 again (this is bourne out by Easimap showing the ECU sensor temps). I was mapping the air temp correction map for bonnet temps of ~40 deg so it was favourable to have it doing this... boy did I overheat though...

 

Diesels run cooler and mine has massive rads. A silent viscous fan and a electric one, lots of sound insulation too, so one might not even know or hear the fan... The 7's close proximity and er lack of sound insulation is chalk and cheese to a modern car.

If the temp is sawing away, something in the design or set up is not quite right.

 

Hants (North) and Berkshire Area club site here

Club meeting pics here

 

 

Edited by - stevefoster on 26 Jun 2005 09:49:41