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Date:         Sat, 29 Jun 2002 01:19:29 EDT
Reply-To:     FrankGRUN@AOL.COM
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Frank Grunthaner <FrankGRUN@AOL.COM>
Subject:      Re: Aux Oil Cooler install...results Aircooled vanagon
Comments: To: wilden1@juno.com
Content-Type: text/plain; charset="US-ASCII"

Stan,

I'll try to answer some of the questions below. I'll precede my comments with $$! In a message dated 6/28/02 12:31:41 PM, wilden1@juno.com writes:

<< OK Frank now that we've got you on the soap box, I've got a few statements and then questions about this RX7 cooler I've been raving about. #1) Are you using the 148 degree (f) thermostat that comes in it.?

$$ Yep, just fine by me! In my experience, 148 is the beginning of the bypass close and at 160 F it is fully closed. So I refer to it as a 160 F bypass thermostat.

#2) The little plunger pushes the thermostat to position one cooling at 148 degrees (I boiled mine and it works) and directs oil through stage one in the cooler, the other oil surplus bypasses, True?

$$ Well, close. The Mazda cooler has an entry chamber and an exit chamber which are coupled two ways. There is a bypass valve between the two chambers that is activated by temperature and pressure. The chambers are also connected to the crossflow radiator channels. So at all times, there are two parallel pathways for oil to flow - across the bypass and down the radiator circuit. The radiator channels are not just open tubes - they have a corrugated spring sheet inside to generate turbulence as the oil flows down the tubes. This increases the efficiency of thermal exchange when the oil is hot but really adds flow resistance at high viscosity. So, when cold, the bypass is fully open, 2 to 5% of the oil flows across the radiator and the remainder goes through the bypass port. As the oil temp exceeds 148-150 F, the bypass valve enters into the bypass port cutting down the effective diameter and therefore the flow. Now the bypass flow resistance increases, the viscosity is lower and perhaps 25% of the oil makes its way through the cooler radiator section. When the bypass valve is fully extended, the port is really occluded and as much as 90% of the flow is through the radiator cooling circuit. The spring and plate now help seal the bypass port. But if the oil pressure goes too high on the inlet side, the bypass port will be forced open again. I've stressed the end points, but the flow partition between the cooler and bypass circuit is a continuously varying function. Blither!

#3) The RX7 Engine generates a full 60 psi at rpms over 2000 so it pushed the thermostat plunger to position two and actuates stage two of the cooler (but the spring causes the plunger to vacillate on my Westy that just puts out 48 Psi at 2400 rpms) giving me needle bump on the gauge. Normal ?

$$ I never got around to measuring the oil pressure relief spring opening point. But throughout much of its operating range, the RX-7 exceeds 75 psi. This pressure relief is for safety reasons - not to overpressurize the cooling coil circuit and to pass oil in case the cooling circuit is blocked. It is not clear to me that the pressure relief valve has been actuated on my system which goes to 90 psi cold. I don't agree with your view of the operation here. But, I am doing this all off the top of the head, so won't be the first time I'm wrong. Nonetheless I get damn good cooling at 35 psi.

#4) Stans going full bore now at 70 mph, 3300 rpms and ginning out 60+ psi and the third stage and full capacity of the cooler is active, True?

$$ I would say that if Stan is processing Aluminum at 70 mph and his oil temperature is above 160 F, he is using the full capacity of the oil cooler.

#5) Does the cooler still bypass some oil when the temperature is +160 degrees (f) and the oil pressure is up in the 60 Psi range ?

$$ Oil cooler always bypasses a small amount of oil at extreme temperatures . The closure between chambers is not a hard valve.

The reason I ask these questions is that removed the thermostat and I tried a bolt between the inlet and outlet chamber and didn't get any better results than with the thermostat. I can only assume that the bypass ports were still open. Since this wasn't a junk cooler I didn't jury rig any slip in tubes or plugging devices to seal them off. Got a way to make it full bore cooling all the time?

$$ Been there, done that. I put together a Viton O-ring seal and bolt so I could measure the pressure drop across the cooler as a function of temperature. In my current system, I have thermal probes at the entrance and exit of the cooler. I also have mounted pressure taps as well on occasion. With the temperature probes, it is very easy to see when the cooler turns on. The temperature difference first begins at about 150 F, is up to 10 degrees by 155 and up to 35 degrees by 165. The pressure measurements were confusing, being related to both temperature and viscosity. More about pressure drops later.

Its 98 here in Dallas and I know it won't hurt to have 100% capacity

$$ Yeah, then Corpus (HOE) must be 108!

useable soon. >>

Frank Grunthaner


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