Cooling a DAX Chevvie V8

[JING]

Hi Chris,

Just reading through your posts. It is not clear if this issue has always been happening or has just started?

The comment below about the lower hose from the radiator being cold does not sound right to me. The flow of water as I understand is from the bottom of the radiator, to the water pump and then via thermostat would flow into the engine if the thermostat trigger temp was met. (i.e. opens up) the water then flows back into the radiator, via a header/expansion tank. So the Hot water flows into the top of the radiator through the radiator to cool it and then back into the engine via the lower hose, which would be warm/hot (about the temp of your water temp gauge). (Happy to be corrected if my understanding is not right) - water temp gauge sensor is on the engine block somewhere.

I think the fan switch/sensor would be in the top hose going into the radiator, which should switch the fan on and off based on the temp setting for the switch. (switches I think would switch fan on at about 185 degrees and switch off when below 170)

I assume that when you start the car from cold the fan does not turn on?

If the switch turns the fan on when the temperature rises this would suggest that part is working. If when you switch the engine off hot the fan should run until the coolant temp has dropped below the sensor / switch setting. This may take some time depending on the switch setting - or it could be faulty.

I hope this helps a little. As mentioned, I can only go by what I understand and always open to learn.

[chris27_blue]

Thanks for comments- will ponder

Was at a car show today, and spoke to another Chevvie V8 owner, and he said it may be thermostat, which hadnt been considered.

The top pipe from the radiator where the thermostat is hosed was warm/ hot at the end of a 45 min drive (Tempo sat at 82 deg so thought the issue was resolved, and it was just the fan switch to swap out) but the bottom pipe was cold. Although the way the water circulates is befuddling me, surely both pipes should be warm/hot ish?

Googling it the suggestions are it is hard to replace, or at least refilling the system is hard to replace? Cant be that hard surley.

[AKBaz]

Chris, mine is a 390Fe and I have no overheating issues whatever the temperature or traffic.

I thought that it might be a problem when building so i made sure that any crud in the waterways was thoroughly cleaned out. I also decided to use the waterless coolant (higher boiling point) and made sure that the fan was shrouded so it pulled cooler air only.

Hopes this helps, Barry

[Chris]

My Southern Roadcraft RV8 uses a twin fan, twin speed with just a a fixed two temperature setting switch
that runs the fans .
As for using an over ride switch, you shouldn't need one but why not fit one, it's easy to do and will give you
peace of mind, it won't fix problems but will give you an option .
I have one and do flick it on occasionally in slow/static traffic and I do use it when at home reversing into my garage and leave switched on for a few minutes to dissipate the excess heat after the engine has being switched off.
The position of you coolant switch could give you a bit of bother if air is present, so proberbly worth a check .
And by the way I do lose a bit of coolant after being stopped, not much but does need a top up occasionally .
The system holds pressure ok and when carefully releasing the pressure cap indicates so.
The other thing is I would think most of us who run these sort of cars will have an override switch .
Hope you get something useful out this.
Chris.

[chris27_blue]

OK

If the large cooling fan worked as it should, my troubles would be much lessened

My thoughts are the bimetallic strip within the switch/stat doesnt function with lowering temperature. The fan came on around 85deg but was still whirring 40 mins later at about 50 deg. not sure if its a timer or temperature drop that should switch fan off.

So the switch needs changing. Where to get one? I will start with car builder and go from there

If cant get a replacement am thinking wiring in an overide switch and place on the dashboard. Least them will have piece of mind knowing the fan is on, then turn off after 10 mins being stationary, although if i use existing wiring this will only be with ignition on.

Not sure it will sort the total problem, but will help




Moving on to coolant. It seems to be disappearing. Dont think its head gasket, and cant see any leaks, am hoping there is a bit of air reducing coolant level at reservoir. The disappearance is getting less and less, so will monitor for a bit.

[chris27_blue]

Thought i would jabber on a bit, and if anyone fells on commenting: Feel free

I'm aware, that in particular with the bigger output engines, cooling is an issue with the Cobra's. Sitting in traffic, at traffic lights, along a lovely seaside promenade at a real crawl, queuing at a car show to get in, dawdling thru town, and watch that temperature gauge creep up. Soon as i get over 85deg sweating starts.

Having also decided to press pedal to the metal a few times, this obvs  beefs up the temperature, but the thru draft of doing(Ahem) 70mph keeps the temp low.

However, on a couple occasions when the Cobra stops for a minute or so (IE Reversing into home garage) coolant seems to eject from the overflow pipe on the expansion reservoir(13lb expansion cap pressure? half full when cold) and sometimes a lot. Why... obvs it has expanded, and the engine is getting hotter when switched off- but would that create a major coolant dump?

Far as i can tell, the "water" temperature gauge sensor is strapped to the pipe that comes out the top of the radiator into the thermostat. Or is it? Is that the cooling fan sensor, and the temperature gauge sensor is close to the thermostat housing gauging the temp of the coolant exiting the radiaator. The coolant can get badly behaved around 100deg even though the boiling point is higher than that? The coolant must be hotter than 100deg somewhere in the system

NB:EDIT sussed that temp gauge sensor is right next to thermostat housing, guessing that it senses water that's been through the radiator. Meaning the copper tube sensor on the return flow from radiator, will be for my temperamental cooling fan.

Is there a core engine temp sensor anywhere, and if so what does that trigger if it goes high? Guessing a warning light of some sort. ATM my infra red temp sensor gun is useful. Temp reads up to 185deg so far. Within 180-210 tolerances of a chevvie i believe.

I think, but yet to be fully investigated, that the temp sensor also activates the 16inch suction fan that sits behind the radiator?

The thing is, it doesnt seem to. The only way i can get the large fan to come on is stopping, lifting the bonnet and turning a small dial up which makes the fan kick in. Great. But then the fan doesnt turn off, even when the temperature of the coolant registers below 80deg? And the fan doesnt work with ignition off- but then the water pump isnt circulating anyway so whats the point?

So how is that fan supposed to operate? Or are some replacement parts need.

I would have guessed that when the temp reaches about 90 deg the fan would come on, and when it drops below 80 it would switch off?

I could wire in an overide switch and just turn the fan on and off from the cockpit- would that be an answer. More effective than turning the heater on when the coolant temp increases, as it doesnt do a lot of help imo anyway.

With an engine full of coolant why would it blow anyway? Is the rad cap not rated correctly

It all needs sussing out, or will be doodling around below 2000revs for a bit

Any help appreciated. Thanks for reading, and letting me drone on