questions about cooling

[Guest]

just a few questions in regards to the cooling on a VR4

fitted a evo alloy radiator with a push type fan setup....

the stock rad pressure cap is 0.9bar,

what does fitting a 1.1bar cap do for the cooling?
any downside to doing this??

also what is considered a safe or max temp the coolant should get to?
(at what point is it considered to high/dangerous)

are radiator hose's all equal? or are some better? i need to replace my upper hose, should i go solid pipe with short-ish hose ends?

also, thermostat's is stock opening temp best?
or would it be wise/unwise to fit a lower opening temp thermo??

 

[SiliconAngel]

the stock rad pressure cap is 0.9bar,

what does fitting a 1.1bar cap do for the cooling?

It raises the max pressure the rad cap can hold. Basically as coolant reaches higher temps it will expand - if it starts to boil, that expansion will be rapid. However, if your coolant boils in a pressurised environment it doesn't actually have anywhere to expand TO, thus raising your boiling point (until something explodes).

Obviously in a radiator with an expansion tank, that won't happen - as the coolant expands it will be pushed into the expansion tank, where it should cool (as it's no longer being heated by anything). However if the engine is being pushed under extreme circumstances (ie at constant high-power on a track or high-performance in extreme ambient temperatures) the coolant may boil and expand into the expansion tank but if it's still too hot it will then overflow out of the expansion tank too. At this kind of pressure, a low pressure radiator cap may leak coolant past it (or even blow the seal completely) as you're talking pretty extreme pressure - with a higher pressure cap it's less likely to blow the seal and thus the coolant will have some chance of recondensing in the expansion tank before its expelled.

any downside to doing this??

No. Well, other than the cost of the cap *shrugs*

also what is considered a safe or max temp the coolant should get to? (at what point is it considered to high/dangerous)

Totally depends on the boiling point of your coolant. I run a 50/50 mix of demineralised water to glycerol which substantially increases the boiling point. Take a trip to your local auto parts shop and read the labels on the concentrated coolants - you'll see different max boiling points listed for each of them (I say each - cheap coolants (especially premix, which is almost universally rubbish) sometimes don't show this though). You should find some which are pretty much pure glycerol with high max boiling points at 50/50 mix, which is what you want.

are radiator hose's all equal?

No

or are some better?

Yes. Reinforced silicone pipes are generally far stronger than stock rubber hoses. This is due to a number of properties - silicone is far more resilient to high temperatures, it's a more 'stable' compound so it lasts longer without cracking or perishing like rubber will, it's smoother so has less resistance to the flow of coolant and good hoses are made with ribbing throughout their construction which vastly improves their strength.

Having said that, stock hoses are a known quantity in that they come from Mitsubishi, a huge manufacturer. Buying brand-name is always a good idea. From what I've seen, Ivan's hoses seem pretty good and I'm yet to hear of any problems with them, although admittedly I don't know if anyone's had them in a tracked car yet.

i need to replace my upper hose, should i go solid pipe with short-ish hose ends?

I'm not a fan of solid rad hoses - they're meant to have heaps of flex 'cause the engine can move around quite a lot in relation to the radiator. You're welcome to give it a go, but personally I'd stick to reinforced silicon.

also, thermostat's is stock opening temp best?
or would it be wise/unwise to fit a lower opening temp thermo??

Personally I don't see the benefit, but I'm first to admit I don't know that much about thermostat design, so maybe someone else can shed some light on this area?

 

[bradc]

I posted this on CVR4 in Carstens thread there:

It will allow the water to get up to higher temperatures (read pressure, hot stuff expands) before the cap lets water out into the overflow tank. When the cap does this, the pressure inside the engine water system drops quickly which can lead to steam bubbles and cavitation, not a good thing. A 1.1 bar cap will mean this will happen less, but let the temperature in the radiator go a little bit higher before opening up.

I wouldn't change to a fully solid hose, as you know the engine does rock back and forth quite a bit. You'd want at least a bit of rubber pipe at either end, I'd say at least allowing for 3 inches of engine movement to be safe

For the thermostat, it doesn't matter too much, a lower temp one will keep the water at a lower temperature on the motorway, but around town there will be little difference as at low speeds the thermostat tends to stay fairly open.

From the JPNZ manual the thermostat begins opening at 82C and is fully open by 95C.

I would interprete that as Mitsi wanting the temp to stay under 95C at all times, What temps are you seeing?

 

[SiliconAngel]

It will allow the water to get up to higher temperatures (read pressure, hot stuff expands) before the cap lets water out into the overflow tank. When the cap does this, the pressure inside the engine water system drops quickly which can lead to steam bubbles and cavitation, not a good thing. A 1.1 bar cap will mean this will happen less, but let the temperature in the radiator go a little bit higher before opening up.

So the cap controls flow to the overflow tank and that's what the pressure rating relates to? I didn't know that *looks goofy*

 

[naughtika]

just wanna add my thoughts into the lower temp thermostat..

I think that if you have one of those variable temp fan controller (like what Frozen's got) and match it with a lower temp thermostat, say 70 deg celcius (evo or fto models)..

that would be better?! whether you're cruising down the highway or stuck at traffic in the city. Since you've got your fans set to activate at a lower temp (75deg celcius) and at 70deg celcius you've got your thermostat fully open.. wouldn't that mean you're cooling your engine better?!

I think that if you use a 90 deg thermostat and match it with a variable temp fan controller (set at 70deg), both parts are contradicting each other, where the fan is restricting the thermostat from fully opening since the fan is already cooling down the fluid before it reaches the thermostat?!

what are your thoughs guys?!

 

[bradc]

Yeah, as long as the pressure in the radiator is below 0.9 bar the cap stays shut. Hence in normal use the overflow water is never actually used.

To give you an idea (although my cap is a 1.3 bar) my radiator water looks radioactive green, just like usual. I filled my overflow tank with normal clear water and didn't put any antifreeze in it at all. In all the time I've had my new radiator in, over about 2000km of driving, the overflow tank is now very very slightly green, only noticable on white paper. A small amount of water therefore has come through, but only a very small amount.

Quite a few of the English members have reported that after a long high speed drive (through germany, lucky bastards) that their overflow tank has emptied itself. That happens because when the radiator cap opens it lets water go from the radiator into the overflow tank. The heat makes the water in the radiator expand so much that it displaces water from the overflow. Now the overflow is still full, but the radiator has say 6 litres in it at high pressure, compared to 7 litres normally. When the car is switched off and the water cools, all of the water in the overflow tank gets sucked back into the radiator, so you end up with 7 litres of low pressure water in the radiator, and none at all in the overflow.

It is also the easiest way to see if you are actually hitting 0.9 bar or 1.1 bar regularly, if there is no water in the overflow tank then it has been displaced as per above.

 

[bradc]

Christian, remember though that you want the engine to be fairly hot so that the oil is at operating temperature and that all the parts are operating at their intended temperatures.

If you are stuck in traffic then the fans will be going, and the thermostat will only be fully open if the water is above 95C. I don't have a water temperature gauge so I don't know what the engine runs at normally, but I'm sure Carsten will tell us what he has seen when he is next online.

If your temps get above 95C, ie the gauge starts to point upwards, then the thermostat will already be full open and the fans will be spinning at max speed, so it doesn't really matter if your thermostat had opened at 50C or 80C, it will still be fully open at 95C

 

[naughtika]

Brad, are you suggesting that using a very low temp thermostat is not ideal, unless you're using it for track !?!?

 

[bradc]

Even at the track it isn't really going to be of any help, once you start pushing it and you get over 95C then the thermostat will be open anyway, so again, it doesn't matter.

 

[Guest]

i see a 89C in normal driving and around 95C when stuck in traffic.. i just think my fans are poo so im putting my stock fans on my aluminum radiator, if i can mod them.

 

[Guest]

at the moment im getting

80-85ish driving,

92ish idling for extended periods of time.

using a 1.1bar rad cap, and i dont think its overflowed yet,
althou my upper hose looks more expanded than ive ever noticed.


i dont/cant see myself using a stock rad hose,
the alignment with the evo rad isnt quite the same

(i can use the stock one its just not 100% how id like it to sit)

what brand or what should i look for in a radiator hose?
are ones you get at super cheap / repco ok??

or does anyone know where i can get lengths of straight red silicone rad hose??

 

[Guest]

the only prob with the silicone hose is that you have to cut it for your water temp gauge.. i was looking at the greddy hard pipe with the thread welded in for the temp gauge. silicone joiners are provided and they look around 3 inch each so it would give you a fair bit of movement.