Fan Switch Placement

[kevin the chicken]

Hi,

 

I have recently replaced the fan switch on my S7 Vauxall C20XE with an adjustable one as the old one had ceased to work and so that I can get the setting spot on. However I am wondering if in copying the previous installment I have made a mistake. The fan switch is plumbed in to an inline housing which is situated between the thermostat housing and the top of the radiator. The engine is supposed to operate at 95c, with the fan cutting in at 100c but the thermostat is supposed to only be fully open at 107c according to the haynes manual for this engine.

My question is will the hot water from the opening stat trigger the fan to operate even though the water has only just come up to temperature and if so would the switch be better off located in the bottom hose away from the stat?

I noticed the temp gauge seemed to cycle up and down as if the stat was opening and closing when I took it out for a test run but wasn't able to stay out for too long as the radiator seems to have sprung a leak now. It may be that the fan temp needs to be adjusted.

This leads to my second question, is it best to try to have the radiator re-cored, mended or should it be replaced with a better unit and if so can anybody recommend one?

 

Regards

 

Kevin

[IanS]

My first thought is that the water temp in the bottom hose (return from rad) is ment to be a lot (20 to 40 centigrade) cooler than the water going into the rad at the top so finding a fan cutting in temp is probably impossible.

As the thermostat is only fully open at 107c I would be setting the fan to come on at around or just above this temperature. There is no point in trying to get more cooling if the thermostat is preventing the coolant circulating.

The fan switch will have some hysterisys, probably at least 5c so if it comes on at 100c then it will switch off when back down to 95c so I would expect some movement in the temperature guage, Having the fan switch overlapping the thermostat range will make this worse.

[kevin the chicken]

Hi,

Been giving this one a lot of thought and asked somebody who builds and modifies cars for a living. We are of the same mind that it would be better for the switch to be in the bottom hose, after all if it is mounted in the top hose then it will be switching the fan on before the radiator has had any chance to impact on the water temperature.This should let the stat control the heat in the engine and the fan the heat in the radiator without interfereing with each other. I am replacing the radiator so it is at least the right time to change it all over and it will make the engine bay less cluttered by hiding some of the plumbing. Thanks for your thoughts on the matter, just goes to show that you should never trust anybody elses installation blindly.

[richardm6994]

in the politest possible terms, you're barking up the wrong tree regards your switch position.

 

Temperature control is done after the water has passed through the engine....not before.

 

My electric fan variable switch came with instructions stating top hose mounting only....I've since changed to an electric water pump and this has a digital controller that varies the pump speed and also triggers the electric fan....the sensor for this is also mounted in the top hose (big bold writing in the instructions).

 

If you think about it logically and not over complicated.....whats more important? the temp of the water in the engine or the temp of the water in the rad? I know the water is circulating but essentially that's it in a nutshell.

[Bob Tucker]

XE engines run pretty hot anyway.....I now use the lower temp thermostat 87 deg IIRC?

But the switch has to go in the top hose in any case.

The engine is likely to overheat if its in the lower one.

 

The thermostat is in the top of the engine for the same reason.

HTH Bob

[kevin the chicken]

hi,

wouldn't be the first time I barked up the wrong tree! I'll take your advice (both of you) and retain the switch in the top hose. Perhaps it may be a good idea to replace the thermostat with the lower temperature one anyway, I did test the current one and it seemed ok but if the XE engines run hot it may be better with an 87 deg one.

regards

Kevin

[richardm6994]

Top rad hose for the switch is the way to go.

 

As for the lower temp thermostat....I've never really understood why people think they will get better cooling performance using a lower temp stat as it only alters the temp at which the stat is 100% open.

 

At 91degrees coolant temperature, a lower temp stat (say 87 degrees) will allow the same amount of coolant to pass through as a higher temp stat (say 90 degrees). The only difference being that the lower temp stat opens before the higher temp stat but once both are 100% open, the same amount of coolant flows through each.

 

[kevin the chicken]

Right, in that case I'll try it with the new radiator first as this should be better than the old one anyway. I'm adverse to spending money if its not needed. You would hope that the stat would be right if its the one vauxhall specified anyway.

Another question that springs to mind that a Redtop owner might be able to help with is what threads are likely to be used in the thermostat housing? The sender for the coolant temperature has a fine tapering thread (well it looks like its tapered) but there is another redundant sender to the left of it which has a much coarser thread which screws all the way into the housing. As this is no longer being used I am using this as a bleed screw to get rid of airlocks but I would like to replace it with a more solid non brass item that won't shear off so easily.

I can't find anything in my shed which fits so I was wondering if its an odd thread?