Cooling system performance in the very cold weather

[rjes]

How are people getting on with the cooling systems in the very cold weather?
If people are not familliar, there is a possible problem with Subaru powered T25's in very cold weather. The thermostat can close regardless of engine temperature if too much heat is lost from the coolant flowing through the heater circuit. This is because Subaru engines rely on the coolant returning from the heater circuit to heat the thermostat wax capsule (which is also the reason a heater bypass is essential in T25 conversions). The result is engine overheating. If you have your radiator fan contolled by the ECU the radiator fan will come on, but it won't have an effect as the thermostat is clodsed.
Anything which causes more heat to be removed from the heater circuit than normal could cause the thermostat to close when it should still be open. This includes:

1. A heater with a higher output than the Subaru heater. This appiles to T25 conversions.
2. More than one heater. This applies in higher spec T25's.
3. Exceptionally cold weather (significantly below zero)

Tom Shiels in Canada makes parts to fix this, as it is a significant problem in conversions in Canadian and Scandanavian winters. I discussed it with him when designing my coolant circuit. He used to live in the UK, and his opinion was that it is not cold enough often enough for his fix to be necessary in the UK.
With my own conversion I have had my fan cut in a few times when it is around -5 in previous winters. Every time it was with both heaters on full while stopped at junctions, and the fan soon cut out again when moving. The temp gauge did not show any significant overheating (note my fan is ECU controlled - your fan will not be a symptom of this problem if it is still controlled by the VW temperature switch).

One customer in the UK has definitely had this happen during the current unusually cold spell (it's -6 here at the moment). However, he has an LPG vapouriser which removes additional heat ffrom the heater circuit.
If this happens to you, turn your heater down or off, and the temperature should return to normal.

I am interested to know how people in the UK who have used the coolant plumbing circuit on my web site are getting on. Anyone else had it happen now it's been colder than a 'normal' winter for a few weeks? If so, do you have a rear heater too? Were your heater(s) on full at the time? Do you have an LPG vapouriser? If so was it running on LPG at the time? How cold was it? Did the coolant temperature drop back to normal once the heater was turned down?
Thanks,
_________________
Regards,

Richard,

R J Engineered Solutions
Quality Subaru Powered VW Components
www.rjes.com

[hansend23]

my systemhas a bypass in the metal return line.my matrix is about as far farward as a t25.[the limo bug].it was 6f here for two weeks.the matrix doesnt get real hot.i wish it did.i wish it put out more heat.

i did notice the fan came on twice durring those really cold weeks.
and i did turn the heater fan off and it went back to normal
my system is used in t25s ive seen here.
hope it helps.
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just do it!

[doppelganger]

in my single cab if i have the heater on the switch is buggered so i can only put it on the slowest fan speed ,ive not noticed anything wrong yet and its a 45 min journey to work at mo.
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[rjes]

Thanks for the feedback. Hansend - your heater bypass may be too big a diameter if it is compromising the heater performance a lot.
_________________
Regards,

Richard,

R J Engineered Solutions
Quality Subaru Powered VW Components
www.rjes.com

[Griff71]

If only this had been posted before i ordered a new thermostat. All of a sudden the crewie has started overheating. (ej25 motor/rjes). Did the normal and tested theremostat on the hob and although it opened water had been boiling for some time so ordered a new one to be sure.

Anyway on fitment this morning in the snow and filling the system with water in 1st instance. It still overheats so i have suspected that the water pump has given up. Anyhow i shall try switching of the heater (1 factory spec fitted) and see if this has any effect.

Keep you posted.

Thanks

Griff

[rjes]

If you've just filled the system you could just have air in it. You can almost never get the last bit of air out without driving the VW a very short distance. Without you cab boil the engine over at idle with the radiator stone cold, as the air seens to sit in the thermostat houisng preventing the wax capsule getting warm and opening. This is easily solved by driving it, which seems to shake the air into circulation in the cooling system, which then ends up in the header tank, as detailed in the filling instructions on my site http://www.rjes.com/html/filling_procedure.html
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Regards,

Richard,

R J Engineered Solutions
Quality Subaru Powered VW Components
www.rjes.com

[baldybeere]

Hi
Im new on the forum. But can isuggest a cooling circuit that works in all weathers and you dont need a heater matrix bypass either. Its called a full flow bypass system. I am an ex MG/Rover engineer and have had a lot of experience on cooling systems. I use this system on my subaru T25 conversion without any issues. It never overheats always runs at correct temperature etc. When i figure out how to put a diagram on here i will put one on. If you techies out there want to get ahead of the game then look up Land Rover freelander 1.8 Cooling systems and also Rover 2.0 SLDi cooling circuit and you will find the answer there. I can assure you it works well and can be fitted with a little bit of pipwork to any of the conversions.

[rjes]

Hello baldybeere,
That's a small world. I used to work with another ex rover heating systems expert. He was very helpful and very interested in what I was doing while developing my Subaru conversion parts. I still have lots of sketches of system desigh ideas he did for me. I think he recommended the exact same system, although we were discussing a slightly different problem at the time. Is that the white plastic external thermostat that I thought looked vaguely like Sputnik (a sphere with lots of pipes sticking out at angles)? If so, I have one here, and intend to experiment with it when I look in to developing a cooing system for bays and splits.
If I remember right the special hermostat had been developed by one of his colleagues, who I think he said had a patent on it. Various people he knew (other Rover engineers, I think) had used them successfully on other engines in kit cars, etc.
If the thermostat I have is the same one you are on about, it's unfortunate that the pipe sizes do not match Subaru / VW hoses at all. No problem once I am 100% sure I have a system which works - I'll be getting moulded hoses made anyway, but I'll need a lot of hose reducers for development!
_________________
Regards,

Richard,

R J Engineered Solutions
Quality Subaru Powered VW Components
www.rjes.com

[baldybeere]

Yes it is a small world the automotive world. Yes the guy you are referrring to is Bill Hutchins. Extremely clever guy. I have the circuit running in my T25 with no issues ill take some pictures if you like. The biggest issue with engineering a robust solution is getting the pipework through down past the bulkhead adjacent to the gearbox. I ended up trimming the flange away a little but its still tight. Ill take some pictures and put them on my next post now i have figured out how to do it.

[rjes]

The guy I used to work with was called John. I know I haven't forgotten his surname, but I can't remember it just now. I guess Bill was the inventor of the thermostat?
I don't think cold climate problem is significant enough in the UK climate to justify the extra hassle for 'normal' T25 conversions. I've only seen the slightest traces of it in the coldest parts last 4 winters, and it's only been a curiosity rather then a problem. It may well be worthwhile in colder climates of for those who also have LPG vapourisers though.
I was planning on trying one on a system for an lawn mower VW with the radiator under the floor, but not in relation the the T25 conversion 'cold climate' problem. It was more to do with the less than ideal radiator location and finding a way of using a very large radiator without also overcooling. Before experimenting with one I was going to come up with a way of loffing exactly what the Subaru thermostat does to find out whether it cycles open and closed or stays half open to regulate the temperature as the engine warms up and when it's up to temperature.

I was going to try the thermostat under the floor rathe rathan in the engine bay. I've not thought about it for a while, but if I remember right having the thermostat further forward also suited the heater plumbing too? It may also allow me to use the same moulded engine bay hoses I already have. I have diagrams of various circuit diagrams and layouts we came up with somehwere. I just need more time to experiment with interesting stuff like this!
_________________
Regards,

Richard,

R J Engineered Solutions
Quality Subaru Powered VW Components
www.rjes.com