Overheating Problems -Almost Ready to Give Up

I have had overheating problems since I bought my '93 Miata a year ago despite replacing a water pump, a head and most of the hoses, some of them even twice. I have spent over $1,000 already. Still the car overheats. It has be so unreliable that I am unable to use it as a daily driver. I have missed most of the autocrosses in the last three months and I am considering putting the car up for sale on e-bay. I have never had so many problems with any kind of car before. My MGB wasn't even this bad. Do I just have a lemon or are these cars just prone to overheating?

Here is everything I can think of, maybe something here will give you an idea -

1. Dirty radiator (inside and/or outside)
2. License plate blocking the airflow (common with Miatas)
3. Cracked head / bad headgasket
4. Fans connected backwards
5. Bad thermostat
6. Bad waterpump
7. All anti-freeze / no water in a marginal system
8. Too small of a radiator for modifications/climate (common in this area)
9. Fan motors dirty, fans running slow
10. Fans not working at all due to bad relay/fuse.


Hope this helps

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Originally Posted by Walsted

Here is everything I can think of, maybe something here will give you an idea -

1. Dirty radiator (inside and/or outside)
2. License plate blocking the airflow (common with Miatas)
3. Cracked head / bad headgasket
4. Fans connected backwards
5. Bad thermostat
6. Bad waterpump
7. All anti-freeze / no water in a marginal system
8. Too small of a radiator for modifications/climate (common in this area)
9. Fan motors dirty, fans running slow
10. Fans not working at all due to bad relay/fuse.


Hope this helps

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If it were all antifreeze and no water that would be a problem?

I'd start by replacing the t-stat and flushing the coolant. If that doesn't work I'd replace the radiator (2008-1993=15 years=lots of scale and buildup in your stock radiator).

Give those a try and see how they do.

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Originally Posted by Snowdoggie

If it were all antifreeze and no water that would be a problem?

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Yes! A 50/50 mixture (distilled water/antifreeze) is much better. You can buy it pre-mixed that way as well.

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Originally Posted by Snowdoggie

If it were all antifreeze and no water that would be a problem?

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Antifreeze has a much lower specific heat than water. I forgot the exact numbers, but if I remember correctly, antifreeze is a bit more than half as effective as water.

Run as little antifreeze as possible. Water Wetter helps a little too.

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Originally Posted by sammm

Yes! A 50/50 mixture (distilled water/antifreeze) is much better. You can buy it pre-mixed that way as well.

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I saw the 50/50 mix last week at Walmart, almost same price. Buy 5-6 quarts (I dunno gallons) of distilled water and a thing of regular preston. I put in a quart of anti-freeze and 5 quarts of water recently (you can go less though).

Chris

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Originally Posted by sammm

Yes! A 50/50 mixture (distilled water/antifreeze) is much better. You can buy it pre-mixed that way as well.

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IMHO, 70/30 is best for this climate.

I also have been using "Liquid Cool" for over 20 years, on the advice of a dirt track racer.

I have seen dragging fans. Ones that run but don't pull enough air.

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Originally Posted by Miatamaniac92

...5-6 quarts (I dunno gallons) ...

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QUARTer of a gallon

or...

4 quarts = 1 gallon

As ken o states, try $10 dollar bottle of water wetter or my recent new purchase of Purple Ice for the spec.

Don't forget a plugged up heater core or a kinked hose will also cause overheating problems.

Have you checked that hidden hose that runs from under the airbox to under the exhaust manifold? If someone used a cheezy aftermarket hose there it may have kinked, restricting flow.

RJ

I'm with Rogue, I use 70% water and 30% antifreeze. I've helped fix 2 overheating miatas just by changing the ratio.

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Originally Posted by Sharpie

I'm with Rogue, I use 70% water and 30% antifreeze. I've helped fix 2 overheating miatas just by changing the ratio.

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Interesting, the Peak antifreeze table below recommends the exact opposite ratio (see bottom). :confused:

http://www.peakantifreeze.com/images...tion_chart.jpg

I had some overheating problems in my 1991 Ford Ranger, and the mechanic told me that I needed a new radiator (the PO never changed the coolant in 16 years). He also said I needed to clean out the rust in the engine. The mechanic told me to drain the coolant, fill up with water, and add 1/2 cup of Cascade dishwashing soap. He said to run it a while and then drain and refill with coolant. He said this works better than anything else he has tried. Anybody out there ever use Cascade for cleaning the engine/radiator?

[QUOTE=motorollow;151663]Interesting, the Peak antifreeze table recommends the exact opposite ratio. :confused:

Is hasn't been -34* in D/FW for quite awhile. ;)

Anti-freeze changes the boiling point, but so does pressure. As already stated, anti-freeze does not transfer the as effectively as water.

Chris

According to the chart, a 3:7 ratio (antifreeze to water) means you're protected down to 4 degrees Farenheit. The freezing point changes much more drastically than the boiling point. I suppose that's why they don't call it antiboil! ;)

Anyway, my questions are:

1. Does the lower amount of antifreeze to water make the heat transfer better (faster)?

2. Do you risk faster corrosion with less antifreeze?

3. What ratio would be good for prep for a track day?

I've usually done 50/50 as recommended but then again, I don't think manufacturers care about the longevity of my radiator and would love to sell me more product than I need.

does it overheat when stopped or moving?

Looking at past climatology, it looks like the lowest ever recorded temps around here are just under 0 degrees F, which a 35% coolant/65% water would cover according to the table above. For me, it isn't worth keeping over 30% coolant (to cover temps less than 4 degrees F) when that situation won't be encountered but a few times a decade.

Here's a link that explains a lot. (Everybody probably already knows this, but just in case, since the table doesn't specifically say so, pure water has a specific heat of 1, and specific heat is the measure of how much heat energy can be absorbed/transferred.)

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Originally Posted by mr brg

does it overheat when stopped or moving?

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When moving.

I replaced the water pump.
I replaced the head.
I replaced the upper radiator hose.
Twice.
The second time with an $60 silicon radiator hose from Moss Motors.
I replaced one of the heater hoses.
Nothing is leaking.
I replaced the thermostat.
I replaced the heat sensor on top of the thermostat.
Both fans are running.
I changed the wiring so that both fans are running at the same time all the time, bypassing the relay that turns one of the fans on when the thermostat hits a certain temperature.

Just now I drained the radiator again. Changed the antifreeze with the Prestone 50/50 mixture. Added one half bottle of Water Wetter.

Drove it around the neighborhood for about 20 minutes. It overheated again.

What's left?

Drain some out and add water. 50/50 not great for Texas.

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Originally Posted by Snowdoggie

I replaced the water pump.
I replaced the head.
I replaced the upper radiator hose.
Twice.
The second time with an $60 silicon radiator hose from Moss Motors.
I replaced one of the heater hoses.
Nothing is leaking.
I replaced the thermostat.
I replaced the heat sensor on top of the thermostat.
Both fans are running.
I changed the wiring so that both fans are running at the same time all the time, bypassing the relay that turns one of the fans on when the thermostat hits a certain temperature.

Just now I drained the radiator again. Changed the antifreeze with the Prestone 50/50 mixture. Added one half bottle of Water Wetter.

Drove it around the neighborhood for about 20 minutes. It overheated again.

What's left?

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Compression check to ensure that there isn't a head/headgasket problem. ( I see you replaced it, but that could still be the problem)

Fans are blowing in the correct direction, right? How does the inside of the radiator look?

Highly unlikely, but I worked on a miata that overheated over 65 mph.
After chasing it like you did, turned out to be timing belt off one tooth.
Ran like a champ but progressively got hotter over 65.

My current Miata doesn't like dirty air. ::Drive2::
If I close it up behind slower traffic it warms up. (Not to overheating)
Move over to clean air, back to normal.
It hates semi's (sorry Paul) ;)

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Originally Posted by Snowdoggie

What's left?

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The radiator.
http://www.miatamx5.com/coolantrerou...antrouting.jpg

make sure the t-state is opening all the way, you certainly have the tray behind the radiator, and maybe you want to try running it with just straight water to see if anything changes. 110* heat is hard on any car though.

I know that my NA tends to overheat when I have my Wabbit teeth in the grill (summertime)... it likes a lot of airflow.

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Originally Posted by POS Racing

The radiator.

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And the heater core. The coolant goes from the back of the head where the temp sensors are through the heater core and out to the back of the water pump to go to the radiator.

The temp sensors are on the back of the head next to the firewall and there are 2. One is for the temp gauge on the dash and the other is for the ECU to monitor engine coolant temps.

The thing you replaced on top of the thermostat is the switch to turn the fans on, it's not the temp sensor.

You can check if it's the heater core that's blocking the coolant flow by putting a U shaped hose in place of the 2 that go to the firewall. That will effectively bypass the heater core.

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Originally Posted by channelmaniac

And the heater core. The coolant goes from the back of the head where the temp sensors are through the heater core and out to the back of the water pump to go to the radiator.

The temp sensors are on the back of the head next to the firewall and there are 2. One is for the temp gauge on the dash and the other is for the ECU to monitor engine coolant temps.

The thing you replaced on top of the thermostat is the switch to turn the fans on, it's not the temp sensor.

You can check if it's the heater core that's blocking the coolant flow by putting a U shaped hose in place of the 2 that go to the firewall. That will effectively bypass the heater core.

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these is some debate over that because the heater returns hot water back to the mixing manifold, then into the motor. Some turbo cars run cooler with a valve in the heater return, if they have not changed water routing.


Mazda really screwed us with crappy cooling on these cars:
tiny mouth / heat exchanger opening
water goes out the wrong side of the head
hot water from the heater recirculates with cold water
radiator could be bigger

Would it be worth it to get one of those $500 aluminum radiators?

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Originally Posted by Snowdoggie

Would it be worth it to get one of those $500 aluminum radiators?

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no, the car should cool with the stock radiator. Check everything else first...if everything checks out, then replace the radiator with something better than stock. Hit up Gary for a koyo.

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Originally Posted by Snowdoggie

Would it be worth it to get one of those $500 aluminum radiators?

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How about a new $150 OEM radiator?

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Originally Posted by sammm

How about a new $150 OEM radiator?

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+1. Unless you spend a lot of time on the track in mid-summer, a $150 OEM replacement radiator will do you just fine.

Slightly more than $150:
http://www.miataturbo.net/forum/showthread.php?t=24517

http://www.turbochargers.com/gallery...90_1.sized.jpg

"To do this group buy, I need 5 people. MSRP on the radiator is $320. MAP (Minimum Advertised Pricing) is $240. If I can get 5 people to commit, I can offer the radiators at an additional 10% off, making the price $216.

Additionally, if I can get 10 people, I will do free ground shipping for everyone."

Chris

This place offers free shipping at a resonable price for anything over $50. Go for the two row radiator.
Linkie 1:
This is a local place off of Regal Row and Irving Blvd that has a TYC sign on the building. Unfortunately, they do not have the two row radiator listed.
Linkie 2: