Wompa164

iTrader: (4)

So, I'm at ends with myself here.

After I got my front mounted intercooler, I started to notice higher than normal water temperatures during highway driving.

So before any harm could be done, I ordered a Fluidyne radiator to aile my problem. I also had the coolant flushed and thermostat replaced with a 180* model that was drilled.

But when I drive on the highway (75mph average) for long periods of time (from Dallas to College Station, about 3 hours), I see temperatures about 98*C the whole way (that's with the A/C off!!), and it's freaking me out - I don't want to loose my water seals.

My city driving temperatures are just fine. Cruising around town I will usually see around 80-85*. But the longer I drive (usually start getting a little more agressive with the revs), the temperature seems to start creeping up and stays around 90* until I sit for a little period of time.

This is important: On the highway, as my speeds increase, my temperatures increase. Cruising around 60, I will see temperatures of around 85*. At 70, I will average temperatures of around 93*C. At 80, it sits at just under 100*C, and I haven't dared go any faster, which really sucks! I want to drive fast, but I don't want to loose my engine!

Before anyone asks - YES, I am using the radiator underpan.


So, before I do anything extreme, I'm going to try some basic stuff. I'm going to replace my alternator/water pump belts, flush the coolant with water+water wetter (what %?) and change the thermostat to a normal, non-drilled Mazda OEM unit. Perhaps Marvelspeed got some air in the system when they filled it back up? If this is the case, could someone post a guide on how to flush your coolant?

https://www.rx7club.com/forum/showthread.php?t=352439

I'm also thinking about sealing up the hood scoop for my now non-existant intercooler. I think the pressure zones and airflow inside the engine bay might be getting screwed up by the air coming in, and somehow be drawing away some of the already little air the radiator is getting. This might explain the temperatures increasing as the speed does - more air coming in at greater speeds disrupts the radiator airflow more.

The other thing I was thinking about trying is cutting off the little bar across the front air dam opening on the bumper, below the intercooler. This might allow the underpan to 'scoop' more air through the front, and force it up into the radiator.

Other than the ideas I posted here, I'm at a loss.

Can anyone contribute some of their own personal experience with this, or offer anything? It would be greatly appreciated!

jon88se

What does the stock gauge read? Replace the radiator cap? Water pump making noise?

Aaron Cake

iTrader: (1)

Since you're running hot on the highway, it's not an airflow issue...Do as you said: replace the thermostat with a Mazda unit, and pull your water pump. Make sure the impeller blades are not corroded into nothingness.

Barwick

I vote thermostat... you *need* a proper thermostat to ensure the flow is regulated (running with no thermostat is actually *not* preferable to having a properly operating one. I think it's got something to do with the dwell time the water spends in the block, rather than just flying through it.

SureShot

Sureshot’s Overheating – check list
1) Replace the thermostat. Make sure it fits. The spring loaded disc under the stat valve must close the bypass port, or guess what?
2) Replace the radiator cap. Low pressure = steam bubbles = spit out coolant.
3) Look for leaks. (same symptoms as #2) Some can be very hard to find. You may have to pressure test it. A common failure spot is the 3/8” coolant line that runs from the top of the rear housing (under the intake runners) to the throttle body, to the BAC, to the water pump. Another one is the heater hose under the oil filter.
4) The fan clutch will slowly start slipping as it ages. The fan should pull really hard up to about 4k when the motor is hot. It should maintain about 4k as the motor revs higher. Sometimes you can get more life from it by bending outward the bi-metal strip on the front of the fan clutch. The cut-in for the series 4 fan clutch is gradual – it pulls some even when cold. The series 5 fan clutch is more on/off.
Banzaitoyota’s checklist
1.Are the Oil Cooler fins clear of debris and clean?
2.Does the Oil Cooler thermostat function properly?
3.Are the Radiator Fins clean of debris?
4.Is the Stock Bottom shroud still in place?
5.Are you running a Dual Belt Pulley on the Alt?
6.Did you install a NEW Water Pump when you installed the engine?
7.Is the bottom hose collapsing under load?
8.Did you have the Radiator and Oil Cooler cleaned and Flushed when installing the rebuild ( AS required by MOST REPUTABLE REBUILDERS)?
9. Have you verified water temps with a real gauge instead of the sock POS?
10. What ratio Coolant to Water are you running?
11. Are you running a new STOCK MAZDA OEM thermostat?
12. Mazda Rad Caps?
13. Stock Fan Shroud installed ( For those of you running stock Mechanical Fan)
14. Electric Fan users: Do you have a Shroud installed at all. Most installations only draw air directly across ~60% of the available core surface area.
15. are the stock deflectors installed around the relays forward of the Radiator Core Support?
16. If 15 is a no: Do you have an plate mounted across the support to direct air-flow?
17. Install a spring in the lower rad hose to keep it from collapsing at high RPM

Another longshot possibility:
My 87 was showing overheating symptoms. What finally fixed it? Would you believe the water pump housing? The aluminum casting behind the pump was eroded by the turbulence of the high revving pump and the previous owner using plain water for some time. The bypass valve seat under the thermostat had about a 4mm chamfer eroded away, and there was a 6mm hole eroded through the internal wall between the inlet and outlet side.
All this bypassing gives symptoms like a partially blocked radiator. I fabricated a repair with Bondo Marine Epoxy Putty Stick. It was still holding year later when I sold the car.

95R2-89TII Ground Zero

LOL, I take it you've had a bit of overheating issues?

West TX RX-7

Ok now listen here. I had the EXACT same problem as you are having the EXACT same way. I was running a 2900cfm electric perma cool fan with no shroud. What was happening is the fan was not comming on for long, it would come on and go off, come on and go off. Changed the Relay and it worked flawlessly. For a while, then it started getting hot again but this time it was staying on and I ended up finding out the fan had gotten water in it and the bearing was not letting it turn smoothly and therefore slower.

What to do first:

See how fast it's turning as it is now. Then jump across from the back of the alternator and see if it speeds up. If it had been comming on and off it could be the temp sensor or relay. If it does get faster you have a bad relay or connection.

If you have a factory fan and shroud I dunno what to tell you unless your underdriving the fan or maybe the clutch on the fan is not locking up completely.

I run about 80-90c most of the time. It'll still warm up to around 95-100c if I'm hauling ***** for a long period.

I bet when your going down the hwy and push in the clutch and get off the gas a few seconds then go back to normal driving it cools down as well. More time for the water to sit in the rad and get cooled off.

West TX RX-7

17. Install a spring in the lower rad hose to keep it from collapsing at high RPM


That is something I never thought of but makes since.