Silicone vs EPDM Rubber Hoses?

MaserMike

MaserMike

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FYI - Was just about to buy some replacement heater coolant hoses for the Testarossa, as the 36year old ones have started leaking.

I was under the impression silicone hoses were far superior, until I read about them being permeable with water loss and explains why they are not suitable for fuel. Also looking at this report:


Not sure of anyone else’s experiences otherwise going to revert back to good old rubber hoses…?
 
I'd personally try to use high quality reinforced rubber. There is some really awful rubber hose on the market these days; stiff, shiny black. Avoid that. You should probably be able to find a few rolls of the various sizes from the OEM suppliers.
 
That’s an interesting report. To my understanding, the hose isn’t permeable to liquid water, but water vapour can make it through the hose wall. The report says that on a truck operated on a two shift cycle (to me, that means about 14 hours a day driving) will lose 20 litres a year. That is 4ml per hour.

I imagine the loss is based on surface area, and a truck will have a greater surface area than a car, so a car would lose less.

For a daily driver, probably a bit of a compromise. For an infrequently used car, it’s probably worth it for the longevity.
 
Zep said:
That’s an interesting report. To my understanding, the hose isn’t permeable to liquid water, but water vapour can make it through the hose wall. The report says that on a truck operated on a two shift cycle (to me, that means about 14 hours a day driving) will lose 20 litres a year. That is 4ml per hour.

I imagine the loss is based on surface area, and a truck will have a greater surface area than a car, so a car would lose less.

For a daily driver, probably a bit of a compromise. For an infrequently used car, it’s probably worth it for the longevity.
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They talk about two types of loss, through the walls and leaks due to hose shrinkage at clamps (for want of better word)
 
Zep said:
Yes, but they wrote that the solution to that is retightening following a heat cycle. The 20 litres in the graph is for permeation only.
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Quite correct. I was completely wrong.

We’ll see, the big hoses on the Vette are silicone, I’ll report back.
 
Thanks gents for the responses, it is a bit like the size of a small truck engine the flat 12 which holds 20ltrs of coolant :D Just also been reading up further including the below, as these heating hoses run the middle of the chassis and up into the cabin (don’t want it rusting inside out) I think I will stick to EPDM and cost is 5x cheaper. Probably outlast me for another >36years:

Hmmm… However I was thinking of using waterless coolant when the system and engine gets completely drained, plus engine out belt change soon. Not sure if it mitigates the problems with permeability though…


www.siliconehose.com

Silicone vs. Rubber Hose

Wondering if silicone is better than rubber hose for your vehicle? Find out the pros and cons of both. Flex Technologies makes silicone hose in the USA.
www.siliconehose.com www.siliconehose.com

DRAWBACKS OF SILICONE
Permeability to oil and fuel
The molecular structure of silicone doesn’t play well with oil, fuel, and other oil-based products. We do not recommend using silicone hoses for any applications where they will come in contact with fuel or oil.

Permeability to water molecules
Silicone is watertight, but water vapor can escape very slowly through the walls of the hose. Think of a balloon that you blow up with air and leave on a table for a week. The air escapes very, very slowly through the walls of the balloon. There’s a similar effect with silicone, and if you have silicone hoses on a car that you use as a daily driver, you’ll find yourself having to replace water in the reservoir from time to time - not because you have a leak, but simply because the water is escaping through the walls of your hose. While silicone hoses are a must for racing applications, some people don’t like them in a daily driver.
 
Do Gates make silicone hoses or just EPDM only?
That might be the reason behind the report.

Anyway, it's good practice to check levels and tyre pressures.
 
My understanding of waterless coolant is that it has a high boiling point. Plus it has a higher molecular mass than water (which has a low mass). If it doesn’t boil to form vapour, then it shouldn’t permeate the hose.

But, there is a big caveat with waterless coolant. It has a lower specific heat capacity than water, so it transports less heat for a given volume flow. This has made me quite reticent to use it, as the flow is basically fixed on an older engine so you will in effect run the engine hotter to transfer the same amount of energy.
 
midlifecrisis said:
Do Gates make silicone hoses or just EPDM only?
That might be the reason behind the report.

Anyway, it's good practice to check levels and tyre pressures.
Click to expand...
Gates also make silicone hoses, so it doesn't look like a biased study.... agreed on regular checking, more worried about vapour escaping and slowly rotting away the chassis+cabin where the hoses are encased in steel not open...
 
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Zep said:
My understanding of waterless coolant is that it has a high boiling point. Plus it has a higher molecular mass than water (which has a low mass). If it doesn’t boil to form vapour, then it shouldn’t permeate the hose.

But, there is a big caveat with waterless coolant. It has a lower specific heat capacity than water, so it transports less heat for a given volume flow. This has made me quite reticent to use it, as the flow is basically fixed on an older engine so you will in effect run the engine hotter to transfer the same amount of energy.
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Useful to know too thanks. The waterless coolant I was going to use to prevent internal corrosion, but I didn't know about the lower heat capacity.... As this engine runs hot and tends to be a bbq on wheels in summer, infact too hot as it suffers from hot starter solenoid issues and overall temp gets hot quickly in traffic - looks like I'll also be sticking to pink water coolant and epdm hoses....
 
Oneball said:
Quite correct. I was completely wrong.

We’ll see, the big hoses on the Vette are silicone, I’ll report back.
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So, did a pressure test on the Vette as there’s been some condensation in the rocker covers. I reckon it’s had 10 hours running and at 15psi about 90% of the silicone hoses were leaking where clamped. All tightened up quite a lot.
 
Oneball said:
So, did a pressure test on the Vette as there’s been some condensation in the rocker covers. I reckon it’s had 10 hours running and at 15psi about 90% of the silicone hoses were leaking where clamped. All tightened up quite a lot.
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Oh right so there’s definitely some evaporation occurring through your silicone hoses by the sounds of it?

I bought in the end some EPDM rubber hoses for the Testarossa and also bought normal pink coolant, all to be fitted shortly.
 
MaserMike said:
Oh right so there’s definitely some evaporation occurring through your silicone hoses by the sounds of it?

I bought in the end some EPDM rubber hoses for the Testarossa and also bought normal pink coolant, all to be fitted shortly.
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I don’t think there’s evaporation. But there’s definitely shrinking that allows the clamps to loosen and the leak at a joint. So I wouldn’t use them if it’s a place that’s difficult to get to eg under the inlet manifold on a 3200.
 
Oneball said:
I don’t think there’s evaporation. But there’s definitely shrinking that allows the clamps to loosen and the leak at a joint. So I wouldn’t use them if it’s a place that’s difficult to get to eg under the inlet manifold on a 3200.
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Gotcha, interesting to know as I wouldn’t have thought silicone to shrink like natural rubber etc. Sounds like sticking to EPDM rubber for the heater hoses at least is a very good idea, a bit of a pig to replace and run through the car…
 
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