JSmith0101

iTrader: (6)

Car:

84 GS original motor
Used SA radiator (good condition) no shroud (I know...)
Used fuel tank (good condition, no rust)

So I've been getting my 84 GS in good shape for the past few months, and today, it's done something sorta new. As I was cruising, about 50 mph, 5th gear, the coolant temp gauge went up, QUICKLY. It was pointing at the line before the H, you know, that one. So I turned around and coasted home, and the car was cooler then. After the car cooled down, I checked and tightened my belts, and went for another trip, no problems.

What could this be a result of.

Another thing, is when I'm cruising, the temp is usually half-way. I feel that is a little high. Is that common for SA rads? Could it be that my carb needs a good rebuild, and new floats, and to be tuned well?

ray green

iTrader: (14)

Check your chassis ground. It is wire screwed into the driver's side strut tower just below the fusible links (on the 84/85s). It gets dirty and/or corroded causing a faulty ground that affects your electrical gauges, especially the temp gauge, making it look like the car is over heating.

Here's a post on a similar problem I had:

https://www.rx7club.com/showthread.p...eadlights+make

JSmith0101

iTrader: (6)

Thanks, Ray. Would you happen to have any pictures of the offender? In the original thread, the pics are dead.

DivinDriver

iTrader: (15)

It's the silver hex bolt below the brown fusible link block, on the shock tower. Immediately below the brake line in this shot. On the stock connection, has a doubled wire lead to a crimped ring connector.

JSmith0101

iTrader: (6)

Yeah, I found it, it was just hiding in plain sight.

Cleaned it up really well. No good. Still hot, for reals.

I'm thinking it's more in the carb, since when the car idles, it cools down.

ray green

iTrader: (14)

Man I like that engine bay! What did you use for the gold paint?

Here's the photo of the chassis ground in my white 84 GSL, the one that was causing all the trouble:



And since I'm a big fan of clean engine bays too here's mine, the ground is just under that fuseable link box:

ray green

iTrader: (14)

Have you felt around your radiator? If there are cool spots or if the hoses are cool when the engine is overheating you may have a problem with coolant flow (old rad, bad thermostat, water pump maybe).

blackdeath647

iTrader: (2)

^^ is your coolant mixture good? i know sounds crazy but mine started doing that after i added a bit too much water on the mix, it will only show over heating every once in a while. so i flushed the system and added 50/50 mix into it and it worked fine again, i also retightened the hoses and made sure there were no leaks.

JSmith0101

iTrader: (6)

Coolant mixtures is 50/50 on the numbers and brand new. All the hoses are warm, also.

ray green

iTrader: (14)

Thermostat? If you've got good circulation and a reasonably good rad and fan, it will provide plenty of cooling when sitting at idle or revving in the driveway.

I was so puzzled by my electrical gremlin (and worried about over heating) that I installed a second mechanical temp gauge to be sure the engine wasn't overheating - it wasn't. Details at:

https://www.rx7club.com/1st-generation-specific-1979-1985-18/second-water-temp-sender-tip-installation-question-631760/

Your engine would have to be very screwed up (like ready to blow) to run hot enough to overcome a properly functioning cooling system.

JSmith0101

iTrader: (6)

I suppose the electrical temp gauge I have wouldn't work very well.

Brand new Mazda thermostat.

Unless the radiator is really bad... but from what I can tell, it maybe has 10% build up in it. My old rad was probably about 90%, and never ran this hot.

The fact I'm not using a shroud should be irrelevant at highway speeds.

It's just so weird that when I'm going faster it shows heating up, and when I slow down and stop it doesn't....

It's GOT to be electrical. As the voltage output increases, the heat does, too. I think I'll try a new ground or fifteen tonight.

JSmith0101

iTrader: (6)

Little update, I think that initial ground change helped a little. It took the car longer to show that it was "hot," but it still showed hot after a few minutes more. I also tried turning all electrical off, and then turning the car off and coasting, no change in the temp displayed.

Are there any companies that make thermocouple temp gauges?

JSmith0101

iTrader: (6)

Another odd thing I just remembered, when I'd really stomp on the gas, the temp would drop.

....What the heck?

1983GSP

air in the system, waterpump going out, lean on the carb settings, or timing advanced too much. check to see if the hoses are collapsing also. and GET A SHROUD!!!! the thermostat on the o.e. cooling fan has to heat up to engage the fan clutch. without the shroud the hot air coming from the radiator is not channeled across the front of the fan clutch. the fan will not engage, and your engine will overheat before enough hot air can engage it. and if and when it does engage, the air that is supposed to go through the radiator will be pulled around the sides and not through the middle like it is supposed to. just my $.02

JSmith0101

iTrader: (6)

At highway speeds, it doesn't matter.

djessence

I believe some would say check your timing and trailing ignition. just for ***** n giggles.

Also can you actually confirm the engine is overheating. Like using a infrared temp gun or hand (iffy). could it be you just have a faulty guage (i know its aftermarket)

DivinDriver

iTrader: (15)

Lower hose got the spring form inside it? If not, they can collapse from suction at higher RPMs, choking your colling system.

Thanks, Ray; I used gold spray enamel, and it was a mistake; turned all soapy-looking after a few months of engine heat. I'm slowly changing things out to a blue clearcoat that takes the heat better. But yeah, the gold looked bitchin for a while!

Kentetsu

If its overheating at cruising speeds, then there are only a few things that it could be. Slipping belt on the water pump, clogged radiator, faulty thermostat. I think that about sums it up.

Dr Rx

My vote is the water pump or thermostat.

JSmith0101

iTrader: (6)

Nope, the gauge is the original.

ray green

iTrader: (14)

The original temp gauge is electrical and as pointed out earlier, prone to ground problems. I would check your other grounds, in addition to the chassis ground that you have redone (but did you check it with a meter?)

Also you can guess about the engine temperature or you can know about the engine temperature. Given the essential reliance of our rotaries on cooling and the various possibilities for failure or error in our 20+ year old stock gauges, I would recommend for all rotary owners to have a second mechanical temp gauge installed.

It provides peace of mind when things are going well and a critical second opinion with the stock gauge gets squirrelly. Plus it just looks cool.













You can also mount your temp probe in the water pump housing.

bliffle

I bought an infra-red remote temp sensor at Harborfreight for $30 and located a problem quickly just by sensing temps around the cooling circuits under the hood.

Turned out my 'new' waterpump (6 months old) had failed because the mechanic over-tightened the alternator fanbelt and that caused the bronze bushing to wearout prematurely. The WP was leaking noticeably from the weephole in front under the bushing.

I installed a new WP and set the belt play properly (I think the FSM calls for 16mm play) and it's been OK ever since.

It turns out that many mechanics customarily over-tighten belts, thinking, I suppose, that if tight is good then overtight is even better. But it is not necessarily so.

JSmith0101

iTrader: (6)

Please note guys, it isn't over heating, just higher than I'd like. It read hot, just once, otherwise, it's comfortably located right in the middle, once it warms up. If I go... ~65-70 it cools off a little more.

I'm getting a mechanical temp gauge next week, because I like the business in town more than the one I would have to drive to. Supporting local economy FTW.

The belts are properly tensioned and the thermostat checks out.

ray green

iTrader: (14)

Maybe you have a bad fan clutch. Combined with not having the fan cowling you may have poor air delivery to the radiator surface. When you get up to speed this isn't such a problem because ram air is doing the job.

Anyway the mechanical gauge will tell you a lot. If it really is overheating, even just a little bit, this will be traced by the mechanical gauge, which will track your stock gauge exactly.

If your stock gauge is to blame (like mine was - bad ground) then your mechanical gauge will show that your engine temp is just fine. Time to go looking for grounds again. Might even be the stock gauge itself, but not likely, only replace the cluster as a last resort.

Good luck.

JSmith0101

iTrader: (6)

That's kind of where I'm leaning, that the shroud just helps to direct the air through the fan better.

Unfortunately, I need an SA shroud.