jlee916

Everytime i drive for about an hour and 15 minutes, my s5 fc would over heat. My coolant reservoir tank would over flow and pushes the coolant out the tiny tube by the plastic white cap. When I top off coolants after a flush, i always fill the reservoir to the full line and made sure my radiator is topped off all the way.

I thought my radiator might be the problem so I swapped it out with a known working one from my parts car last week. Same results after an hour-ish drive on the freeway from the bay area to Sacramento. The only time I take it for these drives with these results are during night time when there's no traffic like 10pm ish.

often times, my thermostat gauge would rise and drop to fine. I understand stock gauge is not accurate, but when I see my coolant tank pushing coolant out and steaming, I'm sure it's accurate this time.

RCCAZ 1

iTrader: (10)

Have you checked your pressure cap? Get a new one and test it prior to install to ensure it holds pressure. Get a tester, pump it up to the indicated crack pressure (13 psi), and ensure that it hold the indicated psi. If it drops off quickly, i.e., loses 1-2 psi in 5-10 minutes, test another cap until you find one that holds pressure. I went to NAPA last year and tested 3-5 caps off their shelf until I found one that worked properly, so just buying a NEW one is no guarantee.

Do NOT buy the ones with the red lever relief handle on top. Those can often be suspect. The rising, then falling again of your temp gauge could indicate air in your coolant system. Make sure you have all of the air out of your system. Get a large yellow Lisle funnel and run the car with the funnel installed and your heater cranked wide open several times to ensure the air is out of your engine and heater core.

If the cap is good and this behavior continues, it's likely coolant seal failure, but check the pressure cap first.

misterstyx69

iTrader: (142)

3 things.
Cap.
thermostat.(OEM thermo Only)
plastic belly tray.

2-N-D-pink

iTrader: (27)

Sounds like a blown engine to me.

Fill engine/rad with water/coolant...do not put the cap back on, pull Egi fuse from engine bay (as if you were to un flood the car) with the fuse off, have some one turn the engine as if they were to start the car. IF the **** spits out of the radiator chances are your coolant seals are done and engine compression is going into coolant passeges. Pushing the coolant out to reservoir then out of the reservoir once filled.

I think the gauge hooks up to the sensor on the rear intermidiate housing. With air in the system, it can make the gauge act up. Or, you can have a bad thermostat not opening and closing as it should.

Also, DO NOT buy a thermostat from the local auto parts store. They are broken. OEM only!

re-rx7

iTrader: (3)

So after an hr his car overheats but he will be able to check for a blown engine by cranking it cold? LOL

re-rx7

iTrader: (3)

So much this. Especially the 3rd one. It would make sense that its graduallt getting hotter from not enough air flow.

clokker

iTrader: (2)

It might "make sense" but that doesn't really mean anything, this has a whiff of truthiness about it.
Just to be a contrarian, I've never seen a difference with/without the undertray, which I think acts more as a rock guard than an airflow panel.

The single biggest improvement in cooling I ever saw came after installing the Volvo front lip (I'd imagine the benefit would accrue to any front airdam/lip). Both fuel consumption and cooling improved and the benefits have remained for over a year now.

@jlee:
How fresh are your cooling system components?
Stuff like thermostat, pressure cap, coolant, belts/hoses and pump?

re-rx7

iTrader: (3)

Well thats funny. I saw 10 degree celcius reduction in temps just from the tray? A whiff of truth. Does air not take the path of least resistance? YOu need to research more.

clokker

iTrader: (2)

I'll get right on that, Rose.

re-rx7

iTrader: (3)

indeed.

clokker

iTrader: (2)

Just out of curiosity, having run with and without the bellypan and noted no significant difference, what "research" should I perform next to better conform to canon?

re-rx7

iTrader: (3)

I suggest you look at the logical reasoning for having a undertray. Airflow follows the path of least resistance. HAve you ever seen a a Vmount without ducting? By your logic there wouldnt be any need since ducting doesnt do anything. With out ducting minimal air will be forced through the radiator/intercooler. Taking the path of least resistance the air will instead try and go under or above the radiator/Ic. Ever seen a race car without ducting all the way up to the rad?

Undertrays are a valuable piece of the pie. Where do you live? If you live in a place that is cooler you may not notice the changes it makes. I live in Texas where the heat is severe and you better believe in 100 degree 80% humidity weather an undertray makes a difference.

jlee916

Thanks for the replies guys.

I need to do a full tune up on these items since these cars are old, and also because I bought it off another guy who didn't know anything about rx7. He told me it was a gtu-s, but I knew that was a lie because it had power everything. Either he was trying to scam me or he was just non-educated about rx7, but nonetheless I got it for a cheap price as a running car with some extra parts. I also picked it up because I needed something to get to work and home at the time.

So far I replaced the radiator with a working one from my parts car. Also replaced the plastic coolant reservoir with another stock one from my parts car. I don't have an under tray on this car, but I did pull one off my parts car a few months ago. Still have it and if that's what plastic belly tray is then I'll bolt it up. Only problem is that it's back in Sacramento, an hour and 30mins-ish away from me.

I'll definitely buy an OEM thermostat and OEM radiator cap along with new belts. My A/C works, but it's not cold after a few minutes. I assume it just needs freon. The overheat problem doesn't bother me much, but it's something I've been putting off and pretending it'll be okay. Up until now, I want to get it settled.

Not sure if this is also a problem, but I noticed if I go up big hills the temp gauge rises too.

re-rx7

iTrader: (3)

]

Knowing that you have AC now, def put the underbelly on.

jlee916

I don't use my AC though. I just turned it on a few weeks ago to see if it does work. That's how I found out it's not cold. I'll still put the belly tray on.

clokker

iTrader: (2)

Unlike you, I haven't employed any "logic", simply reported experientially obtained data.
Given that data, I might use logic to conclude that the FC undertray makes a better rockguard than ducting device, but would not go on to say that ducting in general is not useful.

Airflow management is hardly an intuitive affair and frequently, that which looks "right" is not.

re-rx7

iTrader: (3)

Let it go man. Like I said I backed up my data with numbers logged off my power fc in 95+ degree heat. You probally live somewhere where its cool year around. Bring it down here where it actually gets hot and you will see a difference. You went around everything i posted. Good job. HArdly an intuitive affair. Bwhahaha

re-rx7

iTrader: (3)

The Ac condenser will be one more thing between the air coming in and it getting to the Rad. Air is escaping underneath the car. The undertray provides a barrier from the air escaping and forces it through the rad.

jlee916

cool thanks! definitely going to go back and get my parts this weekend. and yes, clokker lives in denver, so it's kinda cool all year long. last time i was there in may 2012 and september 2012, it was kinda hot as well though. here in the bay area, weather isn't too bad because we're next to the pacific ocean. but up in sacramento, it gets pretty hot which is part of the valley. today was about 106 degrees there i believe.

clokker

iTrader: (2)

Oh, I think not. Good for you.
I gather temp data with my eyes and a VDO gauge in whatever temp happens to be around.
Fond of assumptions, aren't we.
In fact, I live in Denver where it frequently rises above 90°.
Now that we've got that out of the way, explain to me why ducting would be less effective at lower ambient temp. If the FC pan is working, wouldn't the effect be present- perhaps to a lesser degree- at 75° also?
That would require I enter Texas, which I'm loathe to do.

You actually haven't put forth anything more than I- we've both logged data and we've both tried running with and without the bellypan but we got opposite results.
I haven't questioned your veracity, this discrepancy between two very tiny data sets is not uncommon or even unexpected.
What I would question is the willingness to extrapolate your singular experience into a hard and fast rule.

With any luck the op puts on the plastic, the problem goes away and we all carry on doing whatever we do.
But what of your logic and certainty about airflow if it doesn't?

Even if lack of pan is not the primary cause of overheating, you've basically said it will significantly mitigate the symptoms anyway, because the logic of airflow says it must.
We'll see.

welfare

you'd be surprised at how many people are driving around right now, at this very minute, with bad rad caps.
some interesting facts about the effects of pressure and cooling systems; for every psi of pressure placed on the cooling system, there is a 3*f rise in the boiling point of that coolant. that's a 39*f difference between a cap that holds pressure, and one that bleeds it off. staggering!
and likewise, the opposite is true for vacuum. if you place enough vacuum on a system, you could boil the coolant at ambient temp! so just think about that when the cooling system exhales but cannot inhale.
as mentioned,TEST. don't just replace and assume it's all good. i had this very same symptom yesterday (not to say it's the exact same cause). overheated. overflow tank filling right up after highway drive. tested the cap this morning. sure enough, wouldn't hold pressure. went to the junkyard with my tester. 6 or 7 caps later i finally found one that vented at 13psi and maintained it's pressure. 5$ and i'm back in business.
so TEST the cap. first and foremost. it's put under an extreme amount of stress!

2-N-D-pink

iTrader: (27)

Yup. Why not? It happend to me....I drove one of my s4's with a blown engine just like that. Id go to work and before I get there itll over heat...15 min drive. But when taking a long trip (with out stopping) it wouldnt over heat.

I already explained how with blown coolant seals compression will leak into the cooling system. Crank it cold or hot itll still do it. So removing fuel and spark and cranking it will show you blown coolant seals.

Or leave the fuel and spark fuse on...run it cold with out a cap and check for bubbles. Only takes a few mins...if not seconds.

Rob XX 7

iTrader: (8)

You say you fill it to the line, when its cold you mean the "min" or cold Line right? ( i forget which one the fc bottle has )

Driftology

+1 on the belly pan. My vert ran much warmer when I forgot to put it back on. I got worried i was gonna over heat. Only made a difference at speed. I'm in Cali btw.

Dak

Overheating a rotary is not something to be taken lightly( or any car for that matter). It doesn't take many times before the coolant seals could be toast.

As others have said get a new/known working radiator cap. I have seen bad ones that would let the system push coolant out to the overflow but would never draw it back into the radiator as it cooled as it should. After multiple times of this you don't have enough coolant in the system anymore and overheating occurs.

To clokker and re-rx7 do you both have the same radiator? I think this could make a difference if re-rx7 has a stocker lets say and clokker has a Godspeed. The added cooling capacity of the Godspeed may make having less airflow through it a non issue in the driving he does. This is pure speculation. I could take my belly pan off since I have the Godspeed one and temps are hovering in the low to mid 90's in TN but I am to lazy or have too much other stuff to do to bother.