ray green

iTrader: (14)

Here's an interesting web site I found while trying to troubleshoot some odd cooling problems I've been having on my 84 GSL:

http://www.aaroncake.net/rx-7/tech1.htm

It's got a real nice section on cooling problems, especially about the relative merits of clutch and electronic fans, and some important information about using ATF as a "cure all".

Ray

Rx-7Doctor

iTrader: (13)

Ray, that's a great site for people just joining the forum and for those that have been with the forum that are still inexperienced in the basics of Automobile knowledge.

dj55b

iTrader: (2)

Just so you guys know ... Aarons is actualy one of the MODs on here ... so its not just a site that was created just like that. I know him personally too, he lives about 15 minutes away from me

ray green

iTrader: (14)

Ah such a small world. So here's my problem. I recently rebuilt my carb on my 84 GSL and discovered that the car has extra horsepower I wasn't aware of, since neither of my two previous GSLs, nor this one (before the carb rebuild), had as much kick.

As a result I've been getting into the habit of more rapid acceleration and rather prolonged periods of 80 mph+ during my 110 mile interstate commute. The gas mileage is down a bit to about 20 mpg from the usual 23-24, which is to be expected given the more spirited driving.

However sometimes (but not always) when out on the highway doing 70-85 mph, the temp guage starts to creep up past the temp insignia (it's usually just to the left of the insignia, about 1/3 on the guage) and holds reasonably steady just below that little dash at about 2/3 on the guage. It will sometimes stay at this high reading for the entire 1 hour drive. But it never completely overheats and there are no other symptoms, the car is running great.

When I drop back down to average driving speeds the temp guage comes back down to nearly normal after a few minutes, but never really holds steady at that rock solid 1/3 point it should be at.

The next time I drive the car after cooling off, it will be normal and I'll do the whole 110 mile round trip without an incident, even with the prolonged highway travel. Then the next day more "overheating", and so it has gone for the last several months (all reasonably cold ones here in NE GA - curiously I didn't have any problems during the summer months).

So I'm thinking it's the thermostat, which I changed out the first time the problem happened, which did not change the situation at all. I pulled the new thermostat out, tested it, the old one and several others I had lying around in hot water and they all opened fine according to specs. But thermostats are easy to purchase and install, so I going to pick up another one of these, together with a fresh rad cap, just to be sure.

The radiator is a relatiively new (1 year old) aftermarket (from radiators.com) that seems to be working normally, it heats evenly and it worked fine when installed in one of my other GSLs. There are no leaks in the system and no loss of fluid even over long time periods.

The fan clutch seems to work like it should, although I haven't strobbed it yet, but a bad fan clutch isn't consistent with the high speed overtemps anyway. Also I have rotated in two or three different fan clutches without any results.

The coolant is less than a year old and looks like new, the radiator cap is tight, doesn't leak and I've never seen it moving fluid to the overflow bottle, even when the temp guage is up high.

I haven't learned of any easy ways to test the water pump, but it doesn't leak and the upper radiator hose warms up within a minute of the thermostat opening when it gets up to operating temp. You can see the coolant moving when the rad cap is off and the thermostat is open. Also the car has relatively low mileage (117,000) and is in overall good shape, so since the water pump is usually the "item of last resort" I've pretty much ruled this out (mistake?)

And, as I said, about half the time the system works completely normally at all speeds.

So I'm reading the above mentioned web page and Mr. Aarons says something about water pump "cavitation" and the lights come on. Am I really pushing this car beyond it's designed operating range, causing water pump cavitation during prolonged 80-90mph driving? Do I really need to put a pair of underdrive pulleys on my water pump?

Any other ideas?

Thanks!

Ray

Kentetsu

Any chance that your water pump belt is slipping at high rpms?

Natey

iTrader: (19)

Maybe some water wetter would help.

83RxV6

another thing that could cause high temps is a catalitic converter going bad causing exaust gasses to not flow out of the pipes fast enough cutting one out and replacing it is not a bad idea at 117000 miles i have an 83 rx7 and just cut mine out but im in a non emissions legal state where i cut it out completley and put a straight pipe in its place this also produced about 1500 rpm extra per gear and an additional 15 miles an hour per gear just from the free flowing exaust not a bad move on my part at all but like i said we dont have emmission control where i live

ray green

iTrader: (14)

The belts are in great shape and tightly adjusted and I haven't seen any evidence of slipping or funny wear, so I don't think that's it, but then I haven't figured out how to get a peak under the hood at 80 mph (but they don't slip when revved in the driveway).

The cats aren't in there, I've got a bonez replacement pipe in place of the cats with the stock cat back connector pipe and muffler. And yes, getting those cats out and a free flow system in really works wonders.

And to make matters worse, I just got home from work after doing 55 miles out on the highway, most around 90 mph, and the temp gauge didn't budge past the normal operating temp for the whole trip. Same thing when I went in this morning, 55 miles at 80 mph (cops are a little more active in the morning) and it worked perfectly.

But on my way home from work on Friday afternoon it was running hot all the way home. That's when I figured I'd better try to figure out what the problem is.

I'll try the water wetter. In fact, I'll try anything.

Thanks guys!

Any more ideas?

Ray

Rogue_Wulff

Ray, still using the factory beehive oil cooler? I had similar symptoms with my '83 GS, until I went to a FC FMOC.
Remember, the beehive dumps the water returning from the oil cooler, into the lower hose, where it flows back into the engine. Basic design flaw of the beehive, using already heated water to "cool" the oil, then dumping the even more heated water into the engine inlet for a return pass thru.

ray green

iTrader: (14)

Good point, I know next to nothing about the oil cooling system but I was wondering if the problem might be there, since it does a good portion of the engine cooling. I haven't seen anyone talking about oil cooling problems in posts about cooling issues, but this one is weird enough that something like that might explain it.

I do have the factory beehive in there, is there any way to test this system (other than to verify there are no leaks, which I've done)?

Rogue_Wulff

Assuming there are no leaks, oil or water, and that you have sufficant oil pressure, only items I can think of to test are: Crud buildup on the beehive, and crud buildup inside the beehive.
The outside is easy, just looking at it will tell the story. Inside, well that will require a little more effort. Make sure there are no restrictions in the water hoses. The internal water passages can have crud build up in them, just like the rest of the engine.

speedturn

iTrader: (1)

Ray Green: I used to have belt slippage problems caused by the extra load of the mechanical fan. When I got rid of the mechanical fan and went to an electric fan, then all my belt slipping problems went away.

You do not need a mechanical fan to cool your car when running 80 mph, as long as all the ducting and air dam is in place for the radiator to direct the natural ram air flow where it needs to go. If the air is ducted correctly, then no fan is needed as long as the car is moving above 40 mph.

dayton

e-fan will also allow you to set the temp you want the car to operate at... i did the 81-82 radiater and oil cooler conversion on my 85 gsl w/ a black magic e-fan and i love it!!! i used to drive my car from ne atlanta to savannah all the time. i figured that if i wanted this motor to last, then i needed to take care of all the possible weak links... good luck and remember that heat kills!!! (i think i have 189k on my clock currently, and still bang gears every chance i get!!)

trochoid

iTrader: (6)

I can venture 2 guesses/possibilities from the info so far. The clutch fan disengagement may be intermittent. At operating temps and highway speeds, it should be freewheeling, if not, it can restrict air flow. Second item is the lower radiatior hose may be collapsing at higher rpms. Keep in mind the wp pulls coolant through the system, it does not push it. If the hose is collapsing, there are springs made to insert inside of the hose to prevent this. I have noticed the lower hose collapsing, free reving in the driveway.

misterstyx69

iTrader: (142)

Another suggestion is to get the OEM Cap and Thermostat..Some of the aftermarket Thermostats For some strange reason Don't Operate correctly or Give up..get a Madza Brand Thermostat.

jgrewe

iTrader: (1)

I've had to lower hose problems trochoid speaks of. It will collapse sometimes, sometimes it won't. Check that, if you can squeeze it by hand easy get one with a spring in it.

The stock waterpump cavitates about 6200rpm with stock pullies IIRC.

ray green

iTrader: (14)

I've got the OEM thermostats, the cap came with the radiator a year ago, but hey, they're cheap, I'll put some in. Gotta support the Mazda cause afterall.

Trochoid I was wondering about that wire coil in the lower hose, that certainly would account for the situation, but the car can be setting there in the driveway with the temp guage up and the hose looks fine, I think you only need those wires in American cars.

Problem with the fan clutch idea is, and I'd love to blame it on the fan clutch, is that it overheats at 90 mph, on a windy day, in Feb, during a cold snap. I shouldn't even be needing that dang fan.

Oh yeh, I've figured out that I can stick my finger in it (the fan) anytime I want to, except for a few minutes when it's cold. So it's certainly freewheeling and it does the job at low speeds and idling, so it sounds like it's doing all those strange things a fan clutch is supposed to do.

So would an E-fan solve all my problems?

Sounds like a myth, afterall the Mazda engineers were right about everything else. And don't E-fans suck a buch of voltage off the electrical system, then you've got those problems to deal with? Fan clutches must be around for a reason.

So I'll put in some water wetter, new OEM rad cap and thermostat and hope it works.

Thanks for the help guys, in case it doesn't, what should I do next?

Ray

dj55b

iTrader: (2)

I can't remember where i read this, but I know it was from a racer who stated basically the following:

The only time he uses his fan to cool his radiator is after the race he can just keep it on, but during driving, he would always shut it off, because if you need a fan to cool things down it means that things up front aren't being duct properly. He was also mentioning this because i think someone was asking about a bigger radiator and he said that he stock one was more than adequate is everything was done properly, and that adding a bigger one would result only on more weight of the unit itself, and more water to be used in there.

No a direct answer to your problem but something to think about when considering your speed as you mention. Ever stuck your hand outside the window at those speed while trying to have the palm of your hand face towards the car? I would say almost no fans pulls that much air.

ray green

iTrader: (14)

Agreed, I don't think it is the fan but your idea about ducting sure makes sense. But everything looks good up there, the fan shroud is nice and tight and the mud sheild/pan or whatever it's called is in place and in good shape.

It really seems like some kind of partial impedance in the water flow, that's why I was thinking cavitation might explain it, but as I suspected and jgrewe confirmed, the stock pump shouldn't cavitate until 6200 rpm, way past what I'm doing (4000 - 4200 rpm at around 85).

But what if the impeller on the water pump is getting a bit worn out so that it works fine most of the time, but sometimes, at high speed, it starts to cavitate? Still doesn't quite make sense, since you would think the better the pumping action, the more tendency to cavitate.

Next time it happens, I'm going to pull over and pop the hood and have a good look around.

I probably should get one of those lower hoses with the wire in it, like Trochoid suggested, but none of my four GSLs had one of these and I've never had any problem with a collapsing lower hoses before, including this car. The stock hose that's in it is practically new and there is no evidence of collapse (but then, who knows what is happening at 80 mph under the hood?). But it's on my list, if it continues to do this I'll get the wired hose.

Again, thanks for the help!

speedturn

iTrader: (1)

I definitely believe in genuine Mazda thermostats

t_g_farrell

iTrader: (1)

This is just a data point , but I recently replaced the original FMOC hoses on my 80 GS 12a with some new ones (SS ones from Madztrix) and my cooling appears to be much better than it used to be. My temp gauge used to behave a lot like yours and I had changed the tstat, hoses, coolant and it still ran at 1/2 or slightly more on the temp guage. I've yet to split apart the old hoses and see if they had swelled up enough to impede the flow significantly, but I'm thinking it may be the case. Perhaps its a similiar issue with your beehive. I remember reading on this forum that the old oil cooler hoses swell over time and can restrict the flow through the FMOC. Again, not sure if it even applies to the beehive.

mannyvidal

iTrader: (2)

has the idea of a bad temp gauge crosed your mind...

Kentetsu

assuming that your gauge is reading correctly, I'd say that you are definitely looking at a flow problem. You should be able to drive all day at 60+ without any type of fan system.

The only other thought I have is maybe your ignition is too far advanced.

And as far as that spring in the lower hose goes, you won't see it collapsing at idle. This will only happen at high rpms when the pump is pulling hard enough to collapse the hose. Make sense?

CrackHeadMel

iTrader: (2)

intreasting links

however where did he come up with the crazy amp draws the fans have? flexalite site says the black magic draws 13.9 amps

ray green

iTrader: (14)

Bingo, I found the problem.

The clue was that yesterday and today I did the 110 mile commute (220 miles total) and the temp guage held rock steady at the correct running temperature for the whole time, still cruising at 80-90 mph. This is after a week of nearly daily episodes of these high temp episodes out on the highway.

So I'm thinking this is nice and it might even be real, so what happend to this car while it was sitting in the driveway over the weekend?

Not much, on Sunday afternoon I went out to check all the systems - fan clutch worked normally, thermostat came on at the right temp, upper hose got hot and the rad warmed up evenly. Everything looked normal and I didn't "fix" anything.

But then I remembered that when I checked the radiator cap, which is only about a year old and looks new, I got a black smudge on my finger when I rubbed the black rubber seals. So I dressed them with vacuum grease, not so much to fix a leak I didn't think I had, but simply to condition and preserve the rubber seals.

So, to make a short story long, apparently what was happening was the minor oxidation on rubber seals was creating a microporous surface that was allowing air to seep past the seal under pressure, so that the coolant system couldn't fully pressurize the system. Dressing with the vacuum grease removed the pourous surface and renewed the seals so they hold under pressure.

Of couse without full pressure, the coolant couldn't get as hot as it needs to to operate at full efficiency and there might have even been local evaporation zones, creating vapor locks and interfering with coolant flow.

Not a big problem, not enough to cause complete over heating and boil over, but just enough to cause the coolant to run hot when the engine was putting out a lot of heat.

So once again the Mazda engineers have been proven right, their cooling system is completely adequate when properly maintained.

Moral of the story: Change or test your radiator cap whether it looks like it needs it or not. (I noticed the replacement I picked up on the way home has this written on the top).

(Trochoid, Doc and the rest of you rotar heads, I hope you are having a good laugh over this one).

Thanks for the help and some interesting ideas!

I'll get back to you if it turns out I'm completely wrong, again.

Ray