Hey guys. 2007 JDM with 32,000 miles. My car overheats at idle, only when the sun is up. Yeah. Weird. It's 90F over here and it doesn't matter what the ambient temp is, if the sun is hitting the car, the temp would keep on climbing. I monitor my temps using the Torque app. As soon as it gets close to 220F I turn on the heater and it goes down. Whenever I turned the AC back on, it would slowly creep up to 220ish. If I park under a shade, the temp would drop to say 208F. At night, it idles at 204F. Ive noticed that my AC isn’t cold when idling under the sun. It’s a lot cooler when I’m in the shade or at night.

This does not happen when I'm moving. 60mph on the highway, the car sits at around 203F. The AC is a lot cooler as well.

I've replaced the thermostat, flushed the coolant, properly bled the system for air and sealed around the radiator. No luck. Both fans are spinning.

Could it be that the fans are slowing due to age?

I must also add, last year the rubber grommet in the air box tray fell in and jammed a fan. Although the fan still spins, could it be spinning at a much slower rate?

Thanks a lot.

 

There is a chance that sun out = hot pavement = hot air down just off the pavement. This is what you are sucking in to cool the engine. That, combined with a few other things, pretty much keeps cool air away from the radiator. When you hit shade, you are over cooler ground, and get some cool air in.

I suggest reading through the congrats thread below. Specifically do the foam and fan on low mods, in that order, and see if things get better. I think you are in for something like $10 and an afternoon for both together.

 

You need to test that the fans are working correctly on all speeds. What method did you use to bleed the system? have you pressure tested the system?

 

Yes that is what I was thinking. The sun heats up the road/pavement. I've already sealed around the radiator. Fans on low is the only thing left. I didn't do it yet because the AC forces the fans on high. And my problem only happens at idle.

How do I test the fans? My fans come on low speed at 208F and high speed at 214F. I've heard them come on at those temps. Having the AC on forces them on high.

I bled the system by leaving the radiator cap off with the heater on. Revved it a few times. Coolant came out. When the level was stable, I shut the car off. The next morning the level had dropped a little so I topped it off to the Full mark.

I haven't pressure tested the system.

When the grommet fell in, it jammed the fan and my car overheated. The needle went to the 3/4 mark a few times. After I took out the grommet, it didn't overheat again and the fan worked fine.

If there's an internal coolant leak, can the car run slightly hot? I'm asking because the temps are good on the highway (mostly 200F in 93F ambient temps) and I'm not losing any coolant. It's always right at the F mark.

 

That is not the proper way to bleed it, follow the procedure for bleeding the system and testing the fans here:

M A Z D A

You have to think of it as a whole system.

 

Well it's been about one and a half months since I bled the system so I'm guessing all the air must have gone out by now, and the coolant level hasn't dropped.

Both fans spin and they come on at the correct temperatures. Both go on high at 214F. I have seen them spin.

I panic whenever I see 215F. I turn on the heater as soon as possible and then the temp would slowly drop. If I don't turn on the heater, the temp would keep on climbing.

Weirdly, this ONLY happens under the sun. I can idle all day in the shade at 93F ambient temp, and the car would not overheat (temps around 208F). At night, it's around 203F).

Because one fan got jammed from the rubber grommet, could it be spinning slowly?

 

I do not like how how the factory set points let things get. and, if you did not have a way to read temp, you would not even know it was that high. If you have done the foam around the radiator, you can now be pretty sure that when the fans run, they are helping. Go to the congrats thread below and look at the fans on low mod. It involves attaching a wire to one of the legs of a relay fuse to turn it on. You can use a little wire, since it is controlling the relay, not carrying the power.

You can test them by putting a jumper across the larger connectors under the relay. Both fans should come on low when you do this.

You should notice a dramatic drop in temps, at least 10 degrees. If not, time to start looking for a screwed up thermostat or a plugged radiator.

 

But since the AC forces the fans on high, and I'm running the AC on all the time, isn't it sort of pointless? I know it will help, but the fans are on high when this happens.

The thermostat was replaced 2 months ago.

If the radiator is plugged, wouldn't it overheat all the time? Even at speed?

 

Not necessarily.
If it's old or had weak coolant in it, it could have enough rust in it to partially block it, causing it to not flow enough to cool it when it's hot, but allow enough to flow when it's not really hot.
If you have not replaced the radiator recently, and you've exhausted the other possibilities, try a new radiator.

 

Threads like these make my head hurt.

 

But the temp starts to drop as soon as I start to move. This only happens when I'm idling. No matter how high the temp is (I've measured up to 220F), the temp drops as I start to move. Doing 25mph will bring it down to 206F or so.

I know right! I'm so confused. The only explanation is, when the fan got jammed, it weakened the motor, causing it to spin slowly. OR, both my fan motors are spinning slowly due to age. Is that even possible?

 

Yes, you seem to be having trouble understanding that while moving this increases airflow through the radiator which aids in cooling.
I suggest you buy a NEW radiator, and I'd be willing to bet your overheating troubles will be over.

 

But if I'm overheating ONLY at idle, isn't it more likely that the culprit is the fans?

I know that when I'm moving the radiator is getting more air :P

The car came with FL-22 coolant, never changed until 2 months ago. From what I've heard, the coolant is good for 10 years. My cars a 2007 with 32,000 miles. Can my radiator really have a block?

The scientific thing to do is, compare my temps at 30mph with a car that has a good cooling system at the same speed and same ambient temps. What's your ambient temp BigCajun? Could you share your moving temps please?

When I'm on the highway at 60mph, temps drop to around 197F. This is why I sorta ruled out the radiator

 

You could test the fans - just pull the relays out one at a time and jumper the two biggest terminals with some stout wire.

One of my fans was dead for quite a while.

 

The fans work fine. They both turn on at the factory temps, both high and low. I've even individually connected the fans directly to the battery to see if they run, and they do.

One thing I noticed was, the fan on the right side of the car (passenger side for you US folks ) is a lot quieter than the fan on the left side. Is the fan on the left side more powerful than the other? I checked the part numbers on the two motors and they are different. Meaning not the same fan.

 

Check your Radiator CAP.

 

AC on does not turn the fan on high instantly, it only happens when you are already on low speed.

Yes it will. I seen it couple of times.



and leave the cap off is NOT the proper way to bled the system, the easiest way is nose up, add coolant to full, after car warm up rev to 2500-3000 for a min, then rev it to 4500-5000 for another min, fan should be on high speed, let the throttle off , leave it until fan turns off, car off for couple hours, open cap to check coolant level, if not full add it to full. repeat the whole thing until it's done.

 

Yeah that's how they come on. They go from low to high. AC off, the fans will run on low speed until 214F, and then switch to high speed (loud as hell lol).

My point is, the fans come on at the correct temps. The only question is, did the grommet jamming the fan damage the motor permanently, causing it to spin slower than normal.


So since I overheated when the grommet jammed the fan, you think I might have an internal coolant leak? The guage moved to the 3/4 mark But this happened about a year ago and 600 miles later, the car is fine. Starts fine hot and cold and I'm not losing coolant.


I didn't know I had to leave the cap on. Everyone said I should let it idle with the cap off.

Since 2 months have passed, all the air must have got out of the system now, right?

The radiator cap seems to be fine. No cracks. The tabs on the reservoir are still intact. It doesn't seem to be leaking from the cap.

So what you're saying is, with the cap and the internal coolant leak story, if there's a leak in the system, wherever it is, the car can run hot? Because the system is losing pressure?

 

you can check it by checking the power draw


all small leak engine starts fine hot/cold, it's just the matter of time until the leak becomes ... massive. I seen tiny little leaks that's so little that you have to pressure test it for 2 days until u see a bit drop in coolant.




when you don't, you overheat it easily.

you never know

overtime the spring on the cap loses it's force and will release water sooner than it should (less pressure), this is the reason why you should replace the cap every 2-3 yrs. its a cheap insurance that cost like 10 bux.

you never know until it's tested.


you also mentioned your thermostat is replaced 2 months ago, did u align the jig pin correctly ? if u don't, you will ALWAYS have air stuck in the system.

 

Re-Cap..

We think the problem is that the car runs hot at idle, not on highway.

We think that soft foam has been installed around radiator and any openings through the mount, to keep hot air from blowing back around the radiator.

We think the system has been fairly well burped, but the thermostat install may need to be checked.

We think you have done a visual inspection to ensure that is nothing up against the radiator or condenser.

We think the thermostat was installed after the problem manifested itself, and the thermostat is not the problem (correct one, correct temp).

We think that at idle, temps slowly rise until they hit the scary point.

We think that there is no issue at highway speed.

If the car were in my driveway, I would check the foam and jumper the fans on low, then run the car and see what happens. The hood needs to be down for this to replicate back pressure running on the road. If it runs hot, but a big box fan in front of the car and blow air in. If this helps, you still have an air flow problem. Spraying a hose through the grill is an interested test at this point. I am not sure what it means if it works, but it would be good to know. Let me know if it does.

If I could control temps this way, with the AC off, I would leave the fans on low, get a temp controller, or get the ECU set points changed. The problem is likely air flow.

If it did not work, I would start trying to figure out why I am not getting enough hot water through the radiator to cool the engine. That can be a plugged radiator, a plugged water line, crap in the thermostat, a bad thermostat or the water pump is not working like it should at low speed.

My next step would be to raise the RPM to about 1500, and see if the problem gets worse or goes away. This is next because it is an easy test. And, if it cures it, there is likely either something hosed in your water pump or there is a blockage that the water pump cannot overcome at low speed.

If things go well, great. If you still have an issue, I am going to be less useful and the old hands here will be the ones to take note of.

 

Very interesting! I never thought of this. Thanks! But from what I've heard, the way to check the fans is by spinning them by hand. If its harder to spin, then there's something wrong. How would that relate to checking the power draw? If the fans are not spinning smoothly (something to do with the bearings or whatever) wouldn't the power draw be the same and just spinning slowly?


Do our fans REALLY slow down over time or is it just a myth? If so, is checking the power draw the only way to tell?


So a small leak gets big over time?

My car overheated back in May 2014. I monitor my coolant level every week. I even take a photograph of the coolant bottle every week lol. To this day, I haven't lost coolant. It always stays at the Full mark. The color of the coolant hasn't changed either. I'm guessing after a year, if I do have a leak, I would've lost a noticeable amount of coolant, yes?


Thanks. I'll keep that in mind


But I'm not seeing a temp difference between pre and post coolant flush. The car was untouched. Had original FL-22 coolant from the factory.


Alright! Would any radiator cap work? I'm not loosing any water though.


Cant argue with that. Next thing on the list is a coolant system pressure test


I got it done by a shop. I'm sure he put it in correctly because I see no temperature difference pre and post thermostat install (coolant was flushed at the same time). The system was untouched so I'm pretty sure it didn't have air in the system before I replaced the thermostat.

Yes to all The thermostat is genuine from Mazda. Properly installed because there's no temp difference before and after the new thermostat.


Foam is in place I don't think getting the fans to come on early will prevent it the temp rise. When the temps start to climb, the fans are already on high because I'm having the AC on.

I do not have access to a box fan. How much would one cost?

I'll try throwing water at the radiator. It should help lower my temps! :D

Yes, it's most likely airflow. I will try that

When I replaced the thermostat, I found some weird looking stuff inside the thermostat housing. My mechanic said it's rust? We tried to scrape it off. Didn't work much. I'll post a pic of it.


Interesting way to test it out 04Green I will try that and report back!

Hopefully it will Even if it won't, you'll still be one of the honorable members who helped me with this from the start

Thank you so much 04Green and nycgps. You guys are awesome!! We're finally getting somewhere!

 

This is the crap I found inside the thermostat housing. Couldn't scrape it off No idea what this stuff is. It felt rough. Like it was part of the housing.

 

Just found this pic. Some of it was on the old thermostat as well. Felt sorta like dirt. No idea what it exactly is

Sorry for the huge pics lol

 

It's corrosion and it is common on cars with no coolant system maintenance. Like I said, it is a system, addressing one part of a faulty system is pointless. Replace everything and start fresh.

 

One thought for testing is to have the AC off, and just deal with one thing at a time... There is data in how it behaves with fans on low and fans on high. The AC puts a heck of a load on the cooling system. Try working with just the engine to cool. AC off, fans on low.