Before I get all technical, I will begin by unequivocally stating the crux of my argument. I don't see how running 100% Evans NPG is, in real world terms, any different than filling your engine up with 100% undiluted store-brand ethylene glycol, and you wouldn't do that would you? I don't care if Zeus himself urinated in every bottle of Evans NPG+. Running 100% coolant--any coolant--decreases the system's ability to exchange heat no matter what proprietary additives the manufacturer used.

Running 100% coolant--any accepted coolant-- raises the boiling point, at the expense of cooling efficency. We don't need a cooling system that can run at 190C/375F without boiling, and for almost every application localized boiling can be sufficiently mitigated by choosing the right radiator cap and setting up the rest of the cooling system properly. Therefore I am against filling an entire cooling system with Evans NPG+ for almost every application, and I infer that the authors of the SAE standards on coolant would agree with me.

What is Evans NPG+ ?

NPG stands for Non-Aqeuous Propylene Glycol. Non aqueous means there's no water in it, just like a bottle of undiluted green coolant from Walmart has basically no water in it. The + part means they put some proprietary mix of additives in it. You're supposed to drain your cooling system completely dry and then fill everything up with only Evans NPG+ in undiluted form. The high boiling point of Evans NPG+ allows you to run the system without pressure, and such a high boiling point means boiling is completely eliminated. Sounds good right? You'd think every car would run this kind of stuff from the factory...

Concerns about Evans NPG+

I don't know everything about Evans NPG+ because the additives make it a proprietary formulation. But based on what we do know about ethylene glycol and propylene glycol, I argue that there is a negligible difference between running 100% Evans NPG+ (Propylene Glyco + additivesl) and 100% ethylene glycol, which is "regular" coolant you can get anywhere for way cheaper. The boiling points are similar. On Evans website, here is how they list the boiling point at 0psi (no pressure):



375F which is about 190C. Now here is the boiling point for ethylene glycol in undiluted form:


source is wikipedia

That says there is a 387F boiling point for undiluted ethylene glycol. Even if the numbers aren't 100% right, the regular old ethylene glycol in undiluted form is "close enough" in boiling point when compared to Evans NPG+. The difference is that it ethylene glycol is commonly available and it costs less. Ethylene Glycol is less environmentally friendly and I believe is not allowed in some types of racing but that is not a major factor in this discussion.

 

So what about comparing the heat exchanging capability of ethylene glycol and propylene glycol? Let's see what SAE J814 says about this.



We can compare heat exchanging capability by examining the specific heat of a substance. A higher specific heat means that more energy is required to raise the temperature. For our purposes a higher number is better. You can see that at any concentration, the propylene glycol is in fact a better heat exchanger than ethylene glycol by having a higher specific heat. At a 60% concentration there is around a 6% difference in specific heat between the two substances. With Evans proprietary additives the difference may be greater.

However, there is a reason why the Society of Automotive Engineers specifically says "The use of coolant concentrate without dilution... is not recommended" in their document. You know what's a better heat exchanger than both propylene glycol (Evans NPG+) and ethylene glycol? Water. Yeah--the stuff Evans says is bad, which happens to be used in probably every OEM cooling system on production cars available today.



According to Evans own literature above (found this document off Google) there is a 24% difference in specific heat between undiluted Evans NPG at 0psi and a 50/50 ethylene glycol mixture under pressure. Use a % difference calculation for the .66 specific heat of Evans vs .82 for a traditional 50/50 mixture under pressure at 100C.

My Coolant Recommendations

Every setup is different so I will give general principles. For the vast majority of applications I am against running undiluted coolant no matter what that coolant consists of. Water is the best heat exchanger. The more water the better, as long as you can prevent the three downsides: boiling, freezing, and corrosion. Higher pressure radiator caps, good radiators and ducting, and appropriate fan control setups (FC thermoswitch etc) will prevent boiling in most applications.

There is a reason why factory engineers design cooling systems to run a 50/50 mix of coolant and distilled water under pressure. This mixture offers a good balance of corrosion protection, boiling and freezing protection, and the ability to exchange heat. On paper a 50/50 mix of propylene glycol and water will exchange heat better than using ethylene glycol. I am not against propylene glycol or against Evans NPG+ in principle. I do feel their marketing is based on a selective presentation of information on how cooling systems work, and that bothers me. I can't be sure, but I suspect they tell you Evans NPG+ is "incompatible with water" because diluting it lowers the boiling point (which is true to a point) but most importantly, it hurts their bottom line and undermines their marketing efforts. Since it's "waterless" coolant it can't look watery and they have to tell people not to dilute it. Plus they sell another product which help get all the water out of your coolant system.

If you have questions about my sources of data you can PM me.

 

My untested theory as to why people have had success using Evans is that some parts the rotor housings or irons may be exceeding the boiling point of most cooling systems running water or 50/50. If that is the case, it may be better to have less-than-ideal heat transfer vs no heat transfer due to localized boiling.

Your data regarding marketing efforts seems logical. No offense to the salespeople and marketing guys around here, but in my experience many of them have a vague understanding of most technical details unless it is absolutely necessary to close a deal.

 

off topic, but we run water in roadracing because, the two glycols are slippery when they get on the track.

 

I asked the guys at Ron Davis about Evans and water wetter etc, they said they don't recommend either.

 

a few comments:

original NPG is Propylene Glycol + additives

NPG+ is a mixture of roughly 70/30 Ethylene/Propylene before the additives (from their MSDS that I read long ago) as is non toxic

Koenigsegg used to use it as OEM coolant, don't know if they still do.

apart from that, yeah, it should be about the same as running undiluted coolant.

my opinion is that it allows engines to run hotter while keeping the temperatures more even due to the high boiling point that prevents hot spots; this can prevent warpage. Also, running no pressure has some benefits like if there was a leak the system will not rapidly lose all coolant like lower boiling point pressurized systems.

It also never needs changing, I've run it in my FD for over 5 yrs, drag, track, autox, no problem whatsoever.

EDIT: Found MSDS post: https://www.rx7club.com/showpost.php...67&postcount=1

 

my first engine had blown coolant seals at 50k
my second engine had blown coolant seals at 42K.


it was always the coolant groove at around the 12 o'clock position that weakened.

I was a motorcycle mechanic, and former mechanical engineer so you can remove me as the source of human error as I always replaced coolant, radiator caps, hoses. I always replaced coolant when the internal voltage is greater than 0.18 volts.

I switched to NPG+ and coolant seals, 7 years running and never a problem with coolant seal, either overheating or otherwise.

3rd engine - switched to NPG+. 6 years not a problem until I had pre-ignition then it was an apex seal.

BTW, internal coolant voltage always less than 0.02 volt despite being in the car for 6 years. So in theory, theory is never wrong but in practice theory is sometimes wrong. Just look at the financial disaster that engulfed the world. In theory it should had never happened as that was a six sigma event based on theory. In practice it did and it will again because of the reliance on theory without validating practice.

 

We can exchange anecdotes all day long. There are many factors involved. I have had multiple rotary engines running regular 50/50 for many years without coolant seal failure. My Infiniti had the original 50/50 coolant mix in it for 12 years.

Also, I have a bunch of the NPG+ sitting in my shop, enough for a full conversion. When I did all this research I changed my mind.

 

Yes but anecdotes in the aggregate become data. Ulcer was theorized to be caused by stress. When anecdotes from Australia showing that a certain bacteria caused ulcer it was laughed at as being anecdotal. There are many examples of anecdotal evidence which when added up led to a revision of theory.


Your research was based on the flawed assumptions that:
1. the coolant mixture is designed for the intended pressure. wrongo! Mazda reduced the pressure cap from 1.1 to 0.9 bars so now your margin for boiling is lower at the mix ratio of 50/50.
2. radiator cap is holding at rated pressure. I have 7 oem caps at 0.9 and none of them hold that pressure after 3 months in the car. I even used 1.1 caps and again they were not holding after 3-6 months in the car.

I agree that NPG+ is not for everyone due to:

a) cost at $45 per gallon
b) larger radiator is needed (and for non rx7s, higher WP flow rate) to offset the 30% drop in heat transfer
c) error if you have your car serviced by shops where an inadvertent addition of water may occur

But look at the positives:

a) no need to ever replace coolant
b) no electrolytic reaction because water content is less than 5% in the coolant
c) much higher margin for boiling point
d) no issue if your cap is not holding rated pressure
e) cleaner coolant passages (see photos below of rotor housing 6 years with same coolant)

I am not trying to convince you to change to NPG+ but just to counterbalance your recommendations for those in my shoes. REDUNDANCY is the name of the game for my engine: water injection and NPG+

DSC_0038.jpg?t=1300042177

DSC_0037.jpg?t=1300042209

 

The turbo FC ran fine at a .9 bar cap, the Rx-8 ran fine... basically every other rotary has run fine. I'm not saying everybody should run a .9 bar cap. Higher pressure caps are an option that I would choose before running 100% undiluted coolant which has reduced heat transfer capability.

yes we are in agreement here. Except I'd rather have a high capacity radiator with an efficient coolant mixture than a high capacity radiator with a coolant that does not exchange heat as well.

It's an FD. They are old sports cars. You will inevitably be pulling it apart. Then you will either have to catch and reuse the coolant or spend $Texas replacing it when something leaks.

If you want to go by anecdotes, you seem to be one of the few complaining about this. But I don't really want to get too side tracked on that subject.

Nobody wants dirty coolant passages but that's kind of a side issue for most applications. If you are going to lose a motor, it's probably due to knock unless you had a major cooling system component suddenly fail causing an overheat. Super clean coolant passageways won't save you from overboost, a tuning problem, a broken AST or a failed water pump.

And I'm not saying nobody should ever use it because in cars everything is a compromise and trade off. If it personally gives you peace of mind then it's hard to put a price on that. You have the right to configure your car however you want. You've clearly thought this through and I respect your arguments.

I just don't like Evans marketing and I think the drawbacks (cost, lack of availability, poor heat transfer) far outweigh the benefits for most people.

 

when I converted to Evans it was $27/gal wow!

argh, want to sell your stock? how much?

 

Same here, I'm interested in your stock of NPG+.

 

BMW coolant is $35 per gallon of mixed coolant.
Toyota is $29 per gallon of mixed coolant.

In effect a gallon of pure coolant BMW or Toyta is $60 to $70.

But I don't run NPG+ in my other cars as there is no need for NPG+.

 

Thanks for sharing, pomanferrari.

Approximately how many miles did you put on the 3rd engine? Did all three engines re-use the same irons, or were any of them replaced somewhere along the way? Those are very clean coolant jackets in your photos. Do you think the decreased electrolysis will prevent the coolant jacket walls from being damaged over time?

 

found this about rotax aircraft engines recommended coolant:

http://www.rotaxservice.com/rotax_ti...ed4.htm#liquid

 

I put 30,000 miles on the Malloy Reman. Before I purchased it in 2003, I had inspected the internals with a videoscope. The internals (housing, rotors, irons) looked new to me.

Nope, none of the blown engines used any parts leftover from a previous engine. (I do have a fifth engine rebuilt by Howard that came from two blown engines, but that is another story).

I just know that with my previous engines, the water jackets were very dirty and had a whitish powder on them. This one running NPG+ was very clean even though I never changed coolant in almost 7 years. The internal voltage was 0.01 volt in the beginning and at the end. I am still running this same unchanged coolant (but filtered through a coffee filter) in my fourth engine.

 

Look at the head-room until boilover for NPG+ as compared to a 0.9 cap. There is no room for error (e.g., pressure cap not holding 0.9 bars) when using the 0.9 cap or even a 1.1 cap. Despite the lower 30% drop in heat transfer, cost, this factor convinced me to switch.

In Arizona, under 117F ambient temperature, I was running 13psi (no water injection, no 2nd cooler) for several miles to test out NPG+. The coolant temp at the filler neck showed 300F but the car didn't over heat nor did the factory temp gauge went past 1/2 way. When Howard opened this engine, he saw that the dino oil had cooked on the front cover but other than damage due to detonation, the unaffected parts (irons, housing, rotors, crankshaft, oil pump) were in excellent condition.

 

When I switched to NPG my coolant temps dropped about 25degrees. I'be been using it for about 3years with nothing but great results.

 

pomanferrari,

Do you have any close up pictures of the leading and trailing spark plug areas on those rotor housing that used Evans? Interest in the extent of any cracking around the leading plug hole.

Jack

 

A few years ago I had a discussion regarding this topic with the folks at Mazmart.

Summary:

Street cars - yes
Race cars - no

It is especially good for cars that sit a lot for reasons noted in the thread.

For race conditions it simply cannot cool well enough.

Not my opinion, I rely on folks that seem to know what they are talking about.

 

My big thing with NPG is that it's proprietary - if I'm on a road trip away from home and have a coolant leak, I can run to any parts store, grab a jug of Prestone, fix the leak, and be on my way. Can't do that with NPG.

Dale

 

That is an issue. Happened to me once. I just got some distilled water and topped off and ran it like that for a few days w/o issue. Just fyi

 

I used NPG+ for years, but when I lost it all in a race (forgot to torque engine drain after rebuild) I switched to running 100% Sierra pet safe PG coolant.

I have been using 100% Sierra pet safe PG for years now.

Same results

much cheaper

readily available

 

availability is a big deal to a lot of people

they tell you not to dilute it with water for marketing reasons more than anything else

similar to regular Evans NPG (not NPG+)

 

While at SEMA last year, I stopped by the Evans booth to chat with them real quick. I told the sales guy about the concerns I've heard and read here on the forum about what to do in the event of a coolant leak while running Evans. He said you can top off with water or even **** in the radiator if you have to and you wont have problems with their product. The sales guy was cool to chat with and I honestly stopped by their booth for some free M&M's because I was hungry and I got some nice funnels that fit on coolant jugs just for stopping by.