Rotary got hot!

C

C. Ludwig

New member
Ok. Before I even open the hood and look at it (yeah, I'm afraid!
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) let me test the waters here. Just drove a double weekend and during the race on Sunday the water temp shot to around 240-250*. Ambient temp was only 70* and I've run the car just as hard in 85* air with no problems. Temp has always been in the 210* area. Was racing hard for the lead and never looked at a gauge until I fell back a bit after 5 or 6 laps. At that point I decided to ease off and cool the motor. It dropped back to 210* before I ran the last 3 laps pretty hard to hold 2nd. Where do I start looking? Thanks!

Chris

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Chris Ludwig
08 ITS RX7 CenDiv
 
What are you running in place of the thermostat, as a restrictor? Try using a 1/2 inch hole in a block plate, for more restriction, and a longer time for the liquid staying in the radiator. Distilled water only, right?

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Corey L. Clough
ITS RX7 Soon-To-Be
[email protected]
 
I assume your set-up has worked well before, right, so something changed during the race, right? I'm far less an expert than others that frequent this board, but here is where I'd start:
* Are you using the double belt/pulley on the water pump? If not, the single belt can loosed or slip, and then if you're not running with the fan in place the water pump won't turn...
* Some blockage somewhere in the cooling.
* Lower radiator hose collapse (need the hose with wire coil inside.
* Bad Radiator Cap (sorry but I had top ask)
* Something causing cavitation of water at higher speeds (oil in water?)
* Bad water pump
*Or is it an oil cooling problem (failed pump, restriction, etc.)

Let us know what you find out.
 
Chris, the first place you need to look is the radiator. I have 2 7's, 1 was getting hot(in the 240-250 range), the other was running about 200-210. I swapped radiators and the heating problem went away. I hope that there is no heating damage to the motor, 250 is a bit hot for the rotary.

Dennis
 
Looks like it's going to be a water jacket o-ring. Time for a quick lesson in rotary rebuilding.

Thanks for the tips. Everything is new and in spec. Got the dual belts, new pump, distilled water with wetter. According to the guys on RX7 Forums if you remove the pressure cap when the motor is cold, then start it and it pukes coolant out it is probably an o-ring. Makes sense to me. Sounds like something that would be an all or nothing, "just happened" type of failure too.

Chris

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Chris Ludwig
08 ITS RX7 CenDiv
 
I'd be real careful about trusting what the concensus at RX7forums. There's several guys there that I listen to 100%, but most guys are just repeating what others have said.

However, they may be right here. Although I'd be curious about the answers to rlekun's questions before I'd go with that diagnosis.



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I can say that, without opening the hood, I'm pretty certain all the things rlekun's suggestions are covered. With the exception of a blockage. Hard telling what might of worked loose from the junkyard motor. All the other parts are new. I'm gonna have the system pressure tested and that should tell me for certain if one of the o-rings is blown.

Thanks for the suggestions guys!
smile.gif


Chris

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Chris Ludwig
08 ITS RX7 CenDiv
 
Aside from running on someones bumper for a number of laps,poor air flow through the radiator,etc! the guys at ISC are saying that oil temps seem to drive water temps. Thier Fluidyne oil coolers are lowering both oil and water temps with coolant cooling the oil. I think that multi viscosity oils (not made for racing)contribute to even higher oil temps when oil temps rise above 200 degrees. Try a 30-40 wt. synthetic (Redline) racing oil for better lubrication and lower oil temps.
Hope all is well with the 13B!
BB
 
Thanks for the tip. I've had concerns about the oil temps since we broke the car out this spring. They've been around 220-240* very consistently and stayed there while the water got hot this time. I have a second stock cooler mounted but not yet plumbed and am hoping for the cooler temps all around like you're saying. Also plan on switching to a straight weight oil but I have a stash of Mobil 1 to use up first.

I was wondering at first if the temps were the product of running on the leaders bumper for several laps. Once I backed off his tail (OK...he pulled away
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) the temp slowly went back down to 210*. But as soon as I picked the pace up it went back to 240ish.

Chris
 
Chris,
Are you using a thermostat,restictor, gutted stat? Plugged the bypass in the water pump housing?
Belt tension? I believe V belts distort at high RPMs,and with so little belt contact with the water pump pulley, I've wondered if the belts start slipping.
Check out the REDLINE site!
BB
 
Have a restrictor in the pump. Not sure what the size is off hand. And the bypass is plugged. Got the double pulleys on it and the belts aren't "loose", though I don't have them gorilla tight either.

I'm still anticipating an o-ring problem. Will keep you all informed.

Chris



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Chris Ludwig
08 ITS RX7 CenDiv
 
OK. Just did the pressure test. Because my system is kind of a hodge-podge of an early water pump with the pressure cap on the neck and a later radiator with a pressure cap on it's neck I have two caps. The one on the pump is a factory cap rated at about 16lbs. Using that one and plugging the other the system held 15.5lbs for what seemed like as long as I wanted to leave it hooked up. The other cap is rated at 20lbs and likewise the system held 20lbs using that cap for quite a legnth of time.

Soooooooo...

Can I assume that there are no leaks and that the o-rings are OK? Sounds like it to me. Seems the integrity of the system is good.

The pump looks fine and the weep holes are open. So I'm pretty much at a loss. The only thing I can figure is that the situation I was in was really the first time I've rode hard on someone's bumper for several consecutive laps. Maybe the lack of airflow got me in trouble. Certainly didn't help matters. At any rate, I'm gonna plumb the second oil cooler to help lower the oil temps. That will only help the water temps and hopefully keep the problem from showing up again. Man, that sounds overly optimistic!
smile.gif


On a side note. I noticed there is a volume difference between the 86-88 pump and the 89-92. I'm assuming the later pump is better. I have the assembly for the later pump but ruined the housing (don't ask!
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). Is it worth the effort to locate another housing in regard to improved cooling?

Thanks again!

Chris

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Chris Ludwig
08 ITS RX7 CenDiv
 
Chris, I would presume that the volume difference you state is for cooling the motor running at normal road speeds. Most race car applications (street motors)require slowing down the water flow so that the water can do it's cooling job.

Going back to the longwinded chats that were had when you had shown some pictures of your car there was much conversation about air flow through radiators. If I remember correctly. Not that I now it all but did you out engineer yourself in the area of the radiator during you fabricating ? Please don't throw any harpoons
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, just trying present another thought.

David
 
Thar she blows....!!!!
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Just kidding. Hell, maybe. I'm gonna make some changes. Find the newer housing. Mazda Comp says gut a thermostat for a restrictor (gonna try that). Get the second oil cooler going. Stay off the leaders bumper and see what happens. Shouldn't be too hard to stay off anyone's bumper at the next race (M-O) as I've never been there. Ahhhh well. I'm wanting one of those low HP Speedsource motors everyone is talking about in the other thread anyway!!!
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Chris

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Chris Ludwig
08 ITS RX7 CenDiv
 
Don't forget the simple gauge test...put your temperature sender into a pot of boiling water and verify that it reads 212° F on the temp gauge.

Tak
 
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