erasmus229
erasmus229 New Reader
9/4/09 1:01 p.m.

My 79' Rx-7 rally cars gets hot, damn hot, sitting in traffic or idling.( it will overheat in city driving with fan on!) I have an alum. radiator, street port. I run 20-50 oil. I have removed the thermostat but the temp seems to follow the oil temp. I've been thinking of mounting fans on the oil cooler or installing a mister for both the radiator and oil cooler. Would love to reinstall thermostat because it runs cold cruising on the highway (during transits the temp is low 160-170f) Any ideas?

GameboyRMH
GameboyRMH SuperDork
9/4/09 1:51 p.m.

Is your water pump working properly? You could switch to an electric one if it is...

Autolex
Autolex Reader
9/4/09 1:55 p.m.

sounds like it could be a flow problem, either a lack of water flow, or a lack of air flow... Does it have electric fans?

ronbros
ronbros New Reader
9/4/09 3:39 p.m.

most modern cars cant cool properly without a thermostat, unless you block the coolant bypass shut. a 160* is about the best you can get for mazda rotarys, usually they run better with some temp anyway. you may have cooked the coolant seals, 1st test is do you have to add water, often, 2nd fill system full when cool enough to touch, when you start engine do bubbles come up from inside, if yes! time to become a rotary engine mechanic, those early ones are quite simple, and you will have fun.

aussiesmg
aussiesmg Dork
9/4/09 4:16 p.m.

Ron is right, rotaries cannot take even a slight overheating, you have most likely damaged your engine

amg_rx7
amg_rx7 Reader
9/4/09 4:47 p.m.

Could be air in the system also or a bad fan setup. Are you running a shroud for the fan? Is the radiator ducted?

kreb
kreb Dork
9/4/09 6:11 p.m.

timing?

aussiesmg
aussiesmg Dork
9/4/09 6:18 p.m.

SA or FB RX7s do not get air locked pockets as a rule.

Check the fan is a good point, are you running the clutch fan or electric, if electric be aware they do not cool as well as a good clutch fan. The shroud on a RX7 radiator is very important.

P71
P71 SuperDork
9/4/09 8:36 p.m.

A few points, first aluminum radiators are not as efficient as copper. They weigh less and are cheaper, but they do not cool better. Second, a mechanical fan is pretty much required on any rotary, let alone one that is hopped up and rallied. Lastly, 20W50 is way too thick a viscosity for a rotary! Come down to 10W30!

My 12A has 235K+ miles and over 150 autocross runs in the last 20 months, plus 30+ 1/4 mile passes, and is driven nearly daily to boot. 10W30, mechanical fan, copper rad, beehive oil cooler. My Racing Beat header is wrapped, all of the nose/rad ducting is in place (and holes sealed up), and the A/C condenser (and all other A/C parts) are removed. 180* T-Stat, 50/50 coolant, and some RP Purple ICE.

In mid August we had 4 drivers autocrossing, so it ran in the dual driver line twice in a row, with everybody getting 5 runs, non-stop, in 95*+ weather. Never missed a beat or even got hot.

aussiesmg
aussiesmg Dork
9/4/09 8:45 p.m.

Just a note on P71 comment, he is correct about the copper but the real advantage of aluminum is over the brass solder used in a copper radiator, brass is a very poor heat conductor. That is the reason people use aluminum rads.

Weight is not an issue really as the fluids weigh far more than the rad.

BoxheadTim
BoxheadTim New Reader
9/5/09 1:10 a.m.

Definitely reinstall the thermostat, you're not doing most engines a favour by running them without.

If you're running an electric fan, make sure it has the necessary airflow capacity and if not, either run dual fans or fit the mechanical one back. Yes, you get slightly more power with the electric fans but not if you cook your engine at the same time. I'd slightly disagree with P71 regarding the need for a mechanical fan - the FD I owned a while ran fine with electrical fan, but it was designed for it and the fans provided enough air flow to effectively cool the engine.

And as P71 says, you're running oil that's way too thick - 10W40 or 10W30 is the way forward.

fastmiata
fastmiata New Reader
9/5/09 7:37 p.m.

At least install a "gutted" thermostat to control the water flow. Cavitation was one of the real issues on 12A. You might want to make sure that your water pump hasnt lost its impeller.

Feedyurhed
Feedyurhed Reader
9/6/09 6:48 a.m.
P71 wrote: Second, a mechanical fan is pretty much required on any rotary, let alone one that is hopped up and rallied. Lastly, 20W50 is way too thick a viscosity for a rotary! Come down to 10W30! My 12A has 235K+ miles and over 150 autocross runs in the last 20 months, plus 30+ 1/4 mile passes, and is driven nearly daily to boot. 10W30, mechanical fan, copper rad, beehive oil cooler. My Racing Beat header is wrapped, all of the nose/rad ducting is in place (and holes sealed up), and the A/C condenser (and all other A/C parts) are removed. 180* T-Stat, 50/50 coolant, and some RP Purple ICE.

Good advice.

YaNi
YaNi Reader
9/6/09 2:35 p.m.
P71 wrote: Lastly, 20W50 is way too thick a viscosity for a rotary! Come down to 10W30!

Mazda recommends 20W-50 above 15*F for the 13B engine.

bruceman
bruceman New Reader
9/6/09 5:09 p.m.

In reply to YaNi: This is what the Technical Data sayes for 1979: 15F~100F 20W-40, 15F~120F 20W-50, 0F~85F 10W-30, so run 20W-50 if ambient temperature is getting up to 120F

erasmus229
erasmus229 New Reader
9/8/09 10:57 a.m.

I'll reinstall t-stat and drop oil to 10-40 but racing beat is suggesting the 20-50 for 13b race apps. its a 13B 4-port. Engine is still good, no damage from heat, I've done that before. Electric fan but maybe I'll add a shroud. Any suggestions on Rp Purple Ice over Red LIne Water Wetter?

John Brown
John Brown SuperDork
9/8/09 11:48 a.m.

RLWW is better than PI.

Remember when you have a fan issue build a shroud that holds the fan away fron the radiator approximately 1" and make sure no air gets past the fan without going THROUGH the fan. any air gaps will be an easier road for the air than following the control flow. I have built a dozen electric fan setups as well as modifying OE units to non stock applications. remember to add a small weatherseal welt at the shroud contact point and make sure the CFM of the fan is large enough for the engine it is cooling.

Our Preferred Partners
1r7g2Sd31r6ll6OegYHAVTdIgxg0OYjL