This is a continuation of a thread I started in a different section.

I'm running a mid engine with front mounted radiator. Running temperature is between 90 and 95C. To try to bring the temperature down to under 90C I've fitted a higher capacity radiator changing from a 1.0 litre Polo to a VW349 which comes from a 1.9 litre diesel Polo. There has been no change in running temperature. I believe I have sufficient airflow through the rad. I've used 28mm copper pipe from the engine to the rad. I'm wondering if the problem is a question of insufficient water flow.

So, the question is, will an electric water pump help?

Have you had similar problems?

All help much appreciated, thank you.

Isn't the running temperature controlled by the thermostat (as long as the radiator has enough capacity)?

Regards
Hugh

90 to 95 degrees sounds spot-on to me.

95c isn't that hot most cars these days run at around 91c with the fans cutting in on first speed at 105c.

Mid engined cars generally get away with a smaller rad because of the extra cooling area of the pipes -- pays to keep the flow and return well separated. However generally mids need an oil cooler.

If the temperature is correct -- ie checked with a digital probe or infra-red pyrometer then to me it actually souds like a thermostat issue.

You could remove the existing thermostat and plumb in an external Rover/Landrover PRT thermostat which is a fairly cheap Landrover TD5 part PEM100990 --- loads on ebay for 15quid. this thermostat opens at 88c and will open on both temperature and flow pressure --- a lot of MGTF and Lotus Elise owners fit this in the front of the car because it is easier to plumb in at that end.

[Edited on 30/6/10 by britishtrident]
Rescued attachment prt.JPG

Thank you for your replies.

A bit more information on the points you've kindly raised.

1. The thermo switch is the one for the 205GTI which is the engine I'm running and it is the two speed model. From memory it cuts in at half speed at 97, cuts out at 91 and full speed 101 cutting back to half speed at 96. So, with my running temperature, the fan doesn't switch off. Bearing in mind the thermo switch cut in points I would expect the engine to be designed to run at less than 90C.

2 Two thermostats are specified for this engine, an 89C and an 82C. I've now got the 82 one fitted and the running temperature is the same as with the 89 it just takes longer to get there.

My V6 middy has a front mounted Polo rad. I also have a Davies Craig electric water pump (no thermostat)

My running temps can be adjusted via the pump controller but I try and get around 95 as a normal temp with the fan (ecu controlled) cutting in around 100. Using an electric pump also releases a few more horsepower in the bargain as it isn't switched on until needed, and then 'pulsed' as required.

The recent hot weather has seen a rise of about 5 degrees and even in a long traffic jam the most I saw on my Evodash temp gauge was 108 degrees - as my system is pressurised that wasn't a problem.

Winter running (I use my car all year round) proves the cooling system to be too efficient and I revert to 'old school' temp control by blocking off half the rad with some cardboard

To summarise, although you don't mention which engine you are using, the Polo rad should be more than capable of cooling even large engines and the Davies Craig pump is also well up to the job and very adjustable - a very competent setup.


[Edited on 30-6-10 by RazMan]

Thanks Raz. I'm sure the rad is up to the job after all it is fitted to the 1.9 diesel Polo. Engine is 1.6 litres.

I just wonder whether the engine water pump is capable of circulating a sufficient flow over that length of pipework and whether an electric pump would solve the problem.

Did you go for the electric pump straight away or did you have to change to it because of the same problem that I have?

hi, do you have any sort of air return to the header to make sure you are not getting air in the rad? just a thought to iron out.

Yes, there was a return stub on the small Polo rad that I'd fitted initially but there isn't one on the bigger Polo rad that is currently fitted. The problem was the same with both installations so I don't think an airlock or pocket of air in the top of the rad is the problem.

There is enough airflow coming out of the bonnet vent to significantly heat the windscreen so I'm hopeful that airflow is not the problem either.

My feeling is that the rad could take a whole lot more heat away given more flow and that it is the rate of coolant flow that is the problem. I was hoping that other mid-engine builders could confirm this.

in that case then i reckon if other people are suggesting that he temp is fine as it is, then maybe fit an external thermostat switch at the radiator to contol the fan at a higher temp as the only problem it seems is that the fan is on all the time?

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Originally posted by 2cv
Did you go for the electric pump straight away or did you have to change to it because of the same problem that I have?

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I had some issues with my running temperatures (Puma 1.7VCT - see thread here) which got fixed by sorting out the fuel/air mix - it was running too lean and couldn't get rid of the heat quickly enough. Might be one more thing to double check?

I'm using the standard Zetec SE water pump and 32mm aluminium pipes, and I now run at 89-92 all day long with a standard Polo rad up front. Water temperature coming out of the rad is normally 65-70 degrees so there's plenty of spare capacity left. My fan switches on at 104 degrees.

Hope this helps?
Ed.

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The extra length of the pipes shouldn't really affect the pump's performance and it simply gives more coolant to pump round. My central pipes get really warm and it's almost like having a second radiator - inside the car

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Thank you all for your carefully considered replies and for passing on your own findings and experience.

I'm running Webers so no ECU to muddy the waters and as far as I can tell the engine is running correctly.

Apart from trying Water Wetter I think I may have to bite the bullet and go for the electric pump option which does shift serious amounts of coolant and should at least even out the temperature from to back.

I'll keep you posted and thank you again for your help.

Read this and you should be able to work out of the interconnecting piping is too small or not.

I would expect the piping should be bigger than stock as it'll probably 10x longer than as fitted originally.

Thank you for that Doug. Interesting reading. Interesting too to see the recommendation for a larger diameter return compared with the feed. This quote caught my eye;

"A common misconception is that if coolant flows too quickly through the system, that it will not have time to cool properly. However the cooling system is a closed loop, so if you are keeping the coolant in the radiator longer to allow it to cool, you are also allowing it to stay in the engine longer, which increases coolant temperatures. Coolant in the engine will actually boil away from critical heat areas within the cooling system if not forced through the cooling system at a sufficiently high velocity. This situation is a common cause of so-called "hot spots", which can lead to failures."

So, my conclusion; Calculate the conductance of the pipework and try for the highest flow rate possible which should achieve an even temperature throughout the system and as a result, get rid of any hot spots.

Is your bypass return from the thermostat to the engine too large? If so, the coolant will want to go this way rather than the long way round up to the rad and back. I guess this will have the same symptoms as too small a radiator.

ED1801 writes:Is your bypass return from the thermostat to the engine too large? If so, the coolant will want to go this way rather than the long way round up to the rad and back. I guess this will have the same symptoms as too small a radiator.

No I don't think so. It's about a 6mm pipe. Similarly the heater pipes are long and only 15mm copper. The rad is definitely big enough coming from a 1.9 diesel Polo so I'm leaning towards insufficient flow caused by either too small diameter coolant pipes and/or the built in water pump cannot cope.

The short answer is, yes, an electric pump will help, assuming it's higher flow than the OEM part.

The only thing about electric pumps is that they don't last long. Most I've seen seem to be intended for drag-racing cars, where if it lasts 50 hrs, that's a really long time. My concern is that if it fails, how would you know, other than noticing coolant temp is pegged?

My Davies Craig pump has performed faultlessly for over 3 years now - my car has covered 25K miles in that time. I can't remember how long the warranty was/is but if it goes pop I might replace it with a Stewart pump if it has a higher flow rate. As for knowing when it fails, surely the same can be said for conventional pumps - one minute they work, the next ......

[Edited on 1-7-10 by RazMan]

Quote: The only thing about electric pumps is that they don't last long. Most I've seen seem to be intended for drag-racing cars, where if it lasts 50 hrs, that's a really long time. My concern is that if it fails, how would you know, other than noticing coolant temp is pegged

The pump I have in mind is a Craig Davies with a claimed motor life of 2000 hours. At an average speed of 40mph this should give me 80,000 miles. Details of the pump at: http://www.mawsolutions.com/html/ewp80.html

ps can someone please tell me how to do a linky thing!!

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Originally posted by RazMan

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Originally posted by 2cv
Did you go for the electric pump straight away or did you have to change to it because of the same problem that I have?

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I decided to ditch the standard water pump right from the start as they had a reputation for self destructing. They are a remote type on the ST200 V6 and it saved another belt and some engine bay room.

The extra length of the pipes shouldn't really affect the pump's performance and it simply gives more coolant to pump round. My central pipes get really warm and it's almost like having a second radiator - inside the car

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