RX7TR7

I have a bone stock 83 12A with a 5 speed. The radiator had always been a little shaky, though the fill hole you could see some calcium and rust. I installed an electric fan and the car never really ran above 190-200 degrees. The other day I forgot to turn the electric fan on and the car got up to 215-220 degrees. I turned the car off let it cool. I opened the radiator cap to refill what had boiled over and I noticed what looked like whit gravel sitting on top of a bunch of the vanes in the radiator. Im guessing that was calcium. I refilled it with water and took the car for a ride around town and it seemed fine. I drove it around town all weekend with it running right around 185 degrees. I started a new job on Tuesday which requires 20 miles on the highway. At 75 mph my car is at around 3500rpm and the temperature starts climbing and wont stop till it reaches about 210!!!! Now whats strange is anytime the car is stopped or driven slowly the temperature starts dropping and hovers around 180-190. Im used to old cars over heating in traffic not on the high way. So basically I drive to work speeding up in the fast lane and then hit the clutch and coast in the slow lane over and over to keep the temp down so I can get to work, it sucks!! And I dont like risking my car.

I repeatedly flushed the hell out of the block and radiator tonight and that did nothing for me, the thermostat is a 190 and is about 6 months old, so are the hoses, and radiator cap. Ive checked and I have no water in my oil or oil in my water, no white smoke out of the tail pipe, so I dont think I blew the coolant seals. Could it just be the over heat knocked crap loose and it plugged the radiator up?

LongDuck

My guess is, when you overheated it (and 220 isn't disasterously hot) it cooked off a bunch of the calcium that was stuck to stuff inside the engine water passages and possibly the waterpump and radiator. The only place this sediment had to go was out the waterpump to the top of the radiator. The 'white gravel' you see up there is calcium deposits that are now blocking some of the passages at the top and preventing coolant from flowing down through those tubes to be cooled. They could be blocking enough of the coolant passages to allow suction to form on the waterpump inlet side, which would also be bad. You may be able to notice this as the lower radiator hose crimping itself under suction from the waterpump when you rev it a bit at idle. Factory hoses have a spring installed inside to prevent this, but enough blockage will cause the hose to suck up onto itself like sucking on a drinking straw while your finger is covering the other end; when that happens, no coolant is moving at all.

A few things;
1) you mention adding 'water' - you need to add antifreeze safe for aluminum engines, as they not only lower the freezing point, but also raise the boiling point. Straight water will cause problems with internal engine corrosion and hard water will lead to calcium build-up. Use distilled water and antifreeze mixed 50/50.

2) The radiator is cooling at lower engine speeds because the suction side of your waterpump can get enough coolant flowing at low speeds, but not at high speeds. This indicates a blockage on the inlet side - as mentioned, probably due to sediment blocking the radiator tubes from the top.

3) Highway speeds bring lots of cool fresh air in the front, but if the radiator is blocked, it won't matter, and the engine will still overheat.

4) Your thermostat is probably just fine.

5) Your electric fan should be hooked up to a thermal switch mounted inside the TOP radiator hose, that way you won't forget to flip the switch. Overheating a rotary is a quick way to kill it, especially on an older engine with a lot of miles.

6) The stock fan clutch works fine, and is simpler than an e-fan if you get fed up with tinkering with it, and...

Because every list I give has 7 items...

7) Pull your radiator and take it to a radiator shop to have it 'rodded out' - they will unsolder the top tank and run a brass rod down every passage to clear the crap out, clean it, drain it, repaint it, and it will be good for another 100k miles as long as you took my advice above!

Good luck, and get it sorted out because continuing to drive it like this is spiking the temperature at times and running inconsistent and fluctuating temps - which can lead to expansion/contraction on various engine parts that aren't good for it.

RX7TR7

I was running antifreeze that is aluminum safe but 50/50 with tap water. Running straight water has just been the last couple days because I have been fighting with it, and draining and refilling it every day when I get home hoping to remove today's sediment.

On my 77 Trans AM and my 78 mustang when the radiator got crud filled I drained them and capped the radiator inlet and outlet off then filled it with straight CLR and let it soak for a day or two then flushed the hell out of it with water and then water and baking soda and put it back in the car. Usually it works pretty well but I've never had one as bad as this one so I'm not sure if it will work.

I found a 3 core aluminum replacement radiator online for $150 is it worth swapping over to it instead of trying to get mine rodded?

j9fd3s

iTrader: (3)

if it is ok in town but not on the freeway, that suggests that the radiator is plugged.

RX7TR7

Has anyone bought one of these http://www.amazon.com/dp/B00FG8KSOO/ref=dra_a_rv_mr_hn_it_P3081_200?tag=dradisplay-20&ascsubtag=5ac5a2cf427a697d9b4fce1f6a0c4e53_S

TimWilbers

iTrader: (1)

Internet product placement is a wonderful thing. But having the radiator cap on the bottom seems problematic.

I bought a replacement from Mazdatrix as I've had good results from them.

RX7TR7

I think its just upside down in The picture.

LongDuck

I think TimWilbers was just messing with you!

If I had to buy another radiator, I'd also be contacting Mazdatrix. Good luck, and I'm about 95% sure that will fix your problem to replace the radiator.