Radiator/Surge Tank Pressure Cap - Tech

[More Power]

Back in late 1998, I had a 6.5 rad rebuilt at a local shop using a new core. When I picked it up, the shop owner installed a new cap that was rated for 7-psi. He indicated that a lower pressure would make life easier for the water pump seals and reduce the potential for coolant leaks - now and into the future.

Now, I know how pressure raises the boiling point. Still, a 50/50 mix raises the boiling point way higher than we want to run our engines anyway, even at atmospheric pressure.

I've seen numerous posts through the years where someone with a head gasket failure (that overpressurizes the cooling system) and needed to install a new water pump soon after solving the head gasket problem (this happened to me as well with a 6.2). Wouldn't a lower rad pressure be better for water pump life?

So, what are the arguments for running the cooling system at the stock level of 15-psi versus 7-psi?

Jim

[DmaxMaverick]

I've thought about this quite a bit over the years. I like the idea of lower pressure, and I've tried it many ways.

What I found is at a lower pressure, you have to replace vapored off water a lot more often. The water vapors off, but the glycol stays. I have considered having either a 2 tank system, or a condensor in the circuit somewhere. At lower pressure, it may not boil over, but will sure push a lot more liquid back and forth due to the expansion/contraction of the coolant, even below the boiling point. Even so, the coolant is boiling, but it is just happening inside the engine, and condensed as soon as the surrounding coolant shares the heat. If a lower pressure cap is having any effect, that means the coolant is operating at least at the temp, and passing the cap.

This is a good reason to have a close look at products like Evans NPG. No pressure, no expansion/contraction (detectible, anyway) and no boiling. Claims also include more efficient internal heat transfer. I'm changing the coolant in my '01 pretty soon, and the NPG is looking better all the time.

[JeepSJ]

It certainly lends itself to discussion and some testing. There are a lot of old "truths" that have been questioned and reversed. In our racers we have always tried to run 20-21 psi caps to give us as much protection as possible, and I have always run my daily drivers at 16 psi. My new radiator came with a 12 psi cap. I thought maybe they did that because the aluminum radiator could not take the higher pressure, but when I asked I received an answer similar to what Jim got from his radiator guy. I figured that I would give it a shot and see what happens.

[More Power]

As of this point, I can make an argument for both lower and higher cooling system pressure.

For Lower Pressure: Water pump seals last longer.

For Higher Pressure: The vapor layer that forms over the hottest parts of the cyl heads (i.e. exhaust runners) will be less, which should allow a somewhat more efficient heat transfer to the coolant. Just a theory....

Jim

[rustyk]

There's something to be said for sticking with the manufacturer's recommendation. They make it for a reason.:D

[DA BIG ONE]

I've thought about this quite a bit over the years. I like the idea of lower pressure, and I've tried it many ways.

This is a good reason to have a close look at products like Evans NPG. No pressure, no expansion/contraction (detectible, anyway) and no boiling. Claims also include more efficient internal heat transfer. I'm changing the coolant in my '01 pretty soon, and the NPG is looking better all the time.

I've been considering this NPG but worried about keeping system filled up to bleed valve at top on stat housings w/zero pressure it seem to me it can't be done, or am I missin something here?

[DmaxMaverick]

I've been considering this NPG but worried about keeping system filled up to bleed valve at top on stat housings w/zero pressure it seem to me it can't be done, or am I missin something here?

You'll still have the overflow tank to prevent air introduction. As long as it's full and the system doesn't leak, there should be no problem. The system will work the same with Evans, there will just be less pressure. Evans recommends a cap rated at about 2 PSI, and that could be to address your concerns. I don't see it, though. As long as your system is healthy and up to the fill level.

[DA BIG ONE]

You'll still have the overflow tank to prevent air introduction. As long as it's full and the system doesn't leak, there should be no problem. The system will work the same with Evans, there will just be less pressure. Evans recommends a cap rated at about 2 PSI, and that could be to address your concerns. I don't see it, though. As long as your system is healthy and up to the fill level.

This is good news a tight system good to go w/NPG!

Been considering installing that cooling bypass setup from back of heads to stat housing Heath and others have put together, think would this help my 99, or?

[More Power]

I respect Bill's work in a number of areas, but he & I have a difference of opinion about the benefits of his cooling bypass system.

I've studied the 6.2/6.5 cooling system, and know how coolant is transported around inside the block/heads. I believe taking coolant out at the back of the heads would be counterproductive to the health of the cylinder heads.....

Jim

[DmaxMaverick]

I agree with MP. I've studied the coolant circuit, and came to the same conclusion/delusion(?). I think the bypass offers more of a "warm and fuzzy" feeling, being the result will likely show lower temps at the gage. Problem is, if the motor is generating the same amount of heat, the temp sender isn't seeing it. I think what is happening is the coolant is being recycled through the head, retaining heat, not shedding it. If the heat isn't passing the sender, the gage will show "improvement". If it isn't reaching the stat, the problem compounds. I think the actual coolant flow change is minimal, or we'd see remarkable overheating or much more of a temp swing. The reports I've seen have just been a lower indicated temp across the envelope, not fluctuation, like I'd expect. If this mod is allowing the heads to shed additional heat, we should see an increase at the gage, and less extreme fluctuation. In any case, nothing I've seen has changed the trend of head/gasket problems, meaning it is probably not contributing any appreciable benefit, or detriment.

That said, I could be completely wrong. Many mods are speculative, and have varied results. Many times, more than one mod is applied at the same time, which makes it impossible to attribute a result to a specific mod.

[mhagie]

The only benefit I can see in the bypass is to bleed air from the back of the block.
I have found that on my 6.5 it will trap a little air at the back of the head, but on mine I just loosen the glow plug switch and bleed it.
I have run a digital gauge on the rear of cyl head for some time and I noticed that it constantly runs 10* cooler than temps at t/stat housing.
Of course with the coolant path flowing from front to rear in the block before moving up to the cyl heads and back to the front of the engine it stands to reason that the block temps will be cooler than the head where it picks up combustion heat.
I can see no harm to the bypass system if it is done the same way as the Dr Lee oil bypass filter, mainly it needs to have an orface restricting the amount that bypasses the trip to the front of the head.
That said however to me the overall benefit's,if any,of the bypass aren't worth the costs involved to fab the unit in the first place.

Merle

[trbankii]

What is this Evans NPG? A anti-freeze replacement? I haven't run across it before.

[DmaxMaverick]

What is this Evans NPG? A anti-freeze replacement? I haven't run across it before.

Evans Nonaqueous Propylene Glycol. It's a waterless lifetime coolant. Greg at www.lubricationspecialist.com sells it, and his site has a lot of good info on it.

[DA BIG ONE]

This NPG is by far the best thing I've seen to reduce thermal loads on our 6.5td's.

But, where do I get a 2 or 3 lb cap?

[DmaxMaverick]

This NPG is by far the best thing I've seen to reduce thermal loads on our 6.5td's.

But, where do I get a 2 or 3 lb cap?

I think the reduction of pressure loads is near as important. Several benefits to be had there.

Wondered that myself, but I haven't looked for one. I think Evans offers some, as well as other components. One of their suggestions is to modify your existing cap, which I don't think would be too involved. If you snip the spring so the seal just makes contact, it should work. Using the NPG coolant isn't exactly a zero pressure solution. All fluids will expand/contract with the temp to some degree.

[trbankii]

Thanks for the link. That's the first I've run across that product. Have to read up on it now.

[arveetek]

There used to be a member here several years ago who ran Evans NPG in his 6.5L Suburban. I believe he ended up swapping the 6.5L for a Cummins, though, and I haven't heard from him since.

Trying to remember his name.....

Casey

[rustyk]

The coolant system pressure has a function more than stressing seals, etc. Higher pressure also raises the boiling point of the coolant. If one runs the cooling system at atmosperheric pressure (0 psi cap) water boils at 212

[DmaxMaverick]

[quote=rustyk]The coolant system pressure has a function more than stressing seals, etc. Higher pressure also raises the boiling point of the coolant. If one runs the cooling system at atmosperheric pressure (0 psi cap) water boils at 212

[rustyk]

I've looked over the Evans' specs on the NPG+, and one important spec isn't listed - that of "specific heat", which is the amount of heat each unit of fluid can absorb. Water is among the very best fluids for heat transfer, and it's why large stationary engines (as well as those in locomotives and ships) use only anti-rust and some other additives. That and cost...:p

So while the NPG+ can handle higher temperatures, I'd rather avoid them...:D

That's not to say that it won't work fine, but I'd feel better seeing more specs to support the claims.

[DmaxMaverick]

I haven't read their latest specs, but earlier, they did state the specific transfer ability. IIRC, it was less than water, but not by much. I agree, there are very few mediums that are as efficient as water (alcohol or amonia is much more efficient, but not practical/safe), but other benefits may negate that. A key benefit is nearly eliminating film boil, which is the root cause of most instances of hot spots and uneven heat transfer (coolant flow balance being another contributor).

Also in their early literature, they recommended running the system at about 20

[rustyk]

You first! :D

But I wonder if that recommendation isn't based on the lesser ability to transfer heat...

As a totally off-topic note, when I was a field lube engineer, one of my customers (a large shopping center) supplied its own electricity from a bank of Cat generators, which were "ebullient-cooled". The engines were designed to boil off the water into steam, which was then used to heat/cool the center, then be condensed and recovered...

[DA BIG ONE]

I agree, there are very few mediums that are as efficient as water (alcohol or amonia is much more efficient, but not practical/safe), but other benefits may negate that.
.

AMMONIA, now this is real cool when heated, "ice anyone"? if only we can make it safe to even cool down an aftercooler...............I've wondered about this for many years, but a vision of a mushroom cloud over my engine bay has held me back!