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This may be a really dumb question but I have a very rudimentary engine knowledge base.  I am having some cooling issues with my 2020 Beck Speedster with subaru engine.  Granted, I live in Texas and it is already in the mid 90's, but the car has been running a little hot when I am out driving.  Carey and the guys have been great with helping me figure out what the problem is, but I had some free time to look into things and did not want to bother him on his weekend.  Today, I noticed that the radiator fluid seemed a little low.  My question is this.  What coolant should I be using to top off the radiator as well as to add some to the overflow?  radiator



Texas Stu


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Hi Stuart,

My experience with a Subaru engine in a replica is that you want the minimum amount of coolant additive possible, which depends on the annual temperature variations of your area.  If you get a hard freeze, more ethylene or propylene glycol is necessary.  However, maximum heat transfer occurs with plain water.  All other additives decrease heat transfer efficiency.  Since we are car guys, there are lots of discussions as to what type of water works best: tap, distilled, de-ionized, etc.

There are also additives that advertise additional cooling benefits, such as surfactants, that reduce water surface tension, and products such as Water Wetter, that advertise additional cooling benefits.  In addition, water pumps need lubrication to prolong life, so that means another category of additive to coolants.

Air flow through the radiator, coolant speed through the engine, and square footage of rad itself, as well as rad thickness and number of coolant passes in the rad, are all factors that affect engine cooling efficiency.  Cooling fan efficiency, puller vs. pusher fans, and the necessity of an efficient shroud that forces all cooling air through the rad are all elements of keeping coolant temps within range. 

However, the main factor in my experience that raises coolant temp is ambient air temperature.  When air temp rose over 80F, I could expect increased coolant temps.  There are some operator steps you can take to reduce coolant temp, such as lowering engine rpm's, not turning on the a/c, etc., but I'm sure you are taking those steps already.

If your fans come on automatically, you may want to check to make sure they are coming on at the intended coolant temp, and, if you have two fans, that they both come on at the proper fan speed, if you have more than one fan speed.  Depending on your application, there are thermostats that can be adjusted for the fans to start at a lower coolant temp, which can help keep coolant from overheating.

The crew at Beck's is not only talented, but honest as well, and committed to customer satisfaction.  I can think of no other maker who will go further to help solve your problem.  Please keep the group informed as you progress.  That's how we all learn.

I'm not a Subaru guy, but I know enough to know that the cooling system is a weak spot, and I've read enough on this site to know that nobody here (aside from maybe Carey himself) knows more about Subaru cooling than Jim Kelly. But as a guy who deals with heat transfer for money every day, I can tell you his long post above is true in every detail.

Water is a more efficient coolant than glycol (polyethylene, polypropylene, etc.) . There are always other considerations, but for straight heat transfer, glycol of any kind reduces efficiency. The stronger the mixture, the weaker the heat transfer.

@Jim Kelly posted:

Subaru conditioner is Holt's Radweld, rebadged for Subaru.  It's basically another type of Barr's Stop Leak, actually designed for model years 2006 and older.

Yes, it's basically a leak stopper, but it's recommended by Subaru.  I use it in our older Subaru Impreza, but I know of others that use it in newer ones.

Last edited by Bob: IM S6

Carey is the one who can advise you Stuman, as the design of your system is his and he knows the trigger points for the fans etc.

After chasing down the leaks or air pockets after bleeding the coolant system even the type of coolant that they use I would match.  Some Becks also have an auxiliary pump on the older cars.   I won't even talk about never change coolant like Evans .

Best of luck but Careys is your man.

Coolant debate is like oil debate and everyone has their ideas of what to use and what not to use.  I am far form the coolant expert but one thing I do know is you are not supposed to mix colors heavily.  I've seen instances where certain additives will have a bad reaction with other additives and coagulate.

As for what we use: We use Prestone DexCool (orange) with a water wetter additive (1 bottle).  Although I've heard GM techs say DexCool will corrode, clog, etc, we have not excperienced that at all.  Likewise, I've heard to ONLY use Subaru coolant (blue), with mixed reasons as to why (head gaskets, radiator lifespan, etc) but have not experienced this as necessary...

BTW, I got your e-mail @Stuman but my reply says undeliverable.  Not sure if it actually went through or not, but based on your pic, I'd say you had a trapped air bubble, or several small ones that accumulated, and have now purged out of the system, leaving the radiator low.  Top off your radiator, make sure you have a little in your overflow (make it 2" or so just for good measure) and give it a shot.  You may have to repeat a time or two, but that should do the trick.

Not sure what Carey uses on his cars but, the piping is somewhat long on our cars with front radiators, bleeeding the system is an issue that you have to address properly, and if you find the fluid going down, check to see if it is coming out of the overflow tank/tube on your driveway or garage floor after a ride, this happens to some if they do not have a second overflow tank, all turbo's have two tanks and hence adding one might help.

Last edited by IaM-Ray

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