Why does my 5.0 love to run at 210F??

[Evil Joe]

This is an overheating problem I've had for some time. My car just LOVES to run at 205-210 F. So far, I've done the following:

1.) New (very large) 2-core radiator
2.) New 16 psi radiator cap
3.) New Stewart high-flow water pump
4.) New high-flow 180 degree thermostat
5.) New water temperature sending unit
6.) Timing set at 10-11 degrees (new timing chain, too)
7.) Flushed system many times
8.) Coolant: 80% water / 20% prestone
9.) "Burped" system by running car with front end 10" off ground
10.) Bypassed heater core (due to omnipresent leak)

In addition, I don't see any bubbles in the radiator fluid when I rev the engine up with the radiator cap off. I've also checked the compression on the cylinders and they are all good. So, I don't think its a head gasket problem.

I think the only thing left is the guage. But, using a multimeter, I checked the resistance from the temp sending unit as a function of engine temperature and it seems to correlate with the guage. So, I kinda don't think the guage is the problem.

I've noticed that after making all these changes, it pauses around 180F for maybe 10 minutes, then starts to climb to 205-210F and stays there.


I am completely out of ideas. Can someone please, PLEASE help me?


It's an 89 5.0 AOD with 135k miles, all stock except for off-road H-pipe (smog equip still intact), 3.55 gears, and air silencer removed.

[fiveOguy20]

try getting a cooler thermostat, like 160 degrees that might help some.

[PKRWUD]

Do NOT get a cooler t-stat.

FWIW, that's the temp range your engine was designed to run at, but the 180 t-stat should have brought it down 10 degrees. What kind of fan are you using? Is the shroud in good shape? If it's got a fan clutch, what kind of shape is it in?

Fixing the heater core would help, but shouldn't be necessary to bring the temp down. Also, factory gauges suck, if that's what you're using. You really sould confirm the temp with a quality gauge before getting too concerned.

Take care,
~Chris

[Mach 1]

Originally posted by Evil Joe
9.) "Burped" system by running car with front end 10" off ground

Im not familiar with raising the car off the ground to burp it? Is anyone else? All you have to do it run it with the cap off and make sure all the air gets out of the system, and its full. No need to jack the car up?

BTW, if the temp being a little high is gonna drive you nuts, try an aluminum radiator. They work very well. You shouldnt have any problem selling your new 2 core copper/brass, stang parts are easy to unload.

[VeNuM]

Originally posted by Mach 1
Im not familiar with raising the car off the ground to burp it? Is anyone else? All you have to do it run it with the cap off and make sure all the air gets out of the system, and its full. No need to jack the car up?

BTW, if the temp being a little high is gonna drive you nuts, try an aluminum radiator. They work very well. You shouldnt have any problem selling your new 2 core copper/brass, stang parts are easy to unload.

I'm not familiar with this either, I've always just run it with the cap off. When I got my aluminum radiator I noticed a HUGE difference over the stocker. ~Brian

[BilLster]

Well it doesnt say where you live but I always run about %50 antifreeze and %50 water and a bottle of wetter water.(in another post Chris sayes not to run more than 20% coolant I am going to ask him about this because I've always been told coolant also raises the boiling point so maybe this isnt good advice but try wetter watter)

To me I wouldnt say you were running hot . your normal tstat would be 192 so even with a 180 it doesnt open till 180 so its not designed to keep the engine running at 180 just to restrict water flow untill 180.

it also says you have a hi flow water pump we had a problem with a cascar with a hiflow pump that turned out that the flow was to fast for the water (100 water in rad) to absorb heat from the block , we switched back to a stock style pump and it cooled down. I dont think this is your problem cause 205-215 isnt really hot at all.

I would try a better gauge or even see if you can borrow a thermal gauge to test temp. I would add some more coolant to see if it helps with heat transfer.

[GhettoPop]

i have a stock 90 GT w/ 115k miles. At about 110k, i put in a new 3 core rad, stewart water pump, high flow (3 holes) 180 stat, replaced an original cracked fan and replaced the original fan clutch.

the car ran too cold, switched to the standard 190 stat and all problems solved. car runs a little cooler than with the old, original parts.

watter wetter is great, so is orange Havoline Antifreeze which I believe has a watter wetter type additive already in it. I would check out your fan clutch or possible the water pump is defective.

[PKRWUD]

Originally posted by BilLster
Well it doesnt say where you live but I always run about %50 antifreeze and %50 water and a bottle of wetter water.(in another post Chris sayes not to run more than 20% coolant I am going to ask him about this because I've always been told coolant also raises the boiling point so maybe this isnt good advice but try wetter watter)

This is a very common misunderstanding!

A 50/50 mix in the radiator is WAY too much coolant! Especially in warm climates. You will rarely ever require more than 30% coolant/anti-freeze, and even then, only if you live within the Arctic Circle. 20% would be more practical. Coolant serves five purposes, none of which keeps the engine cooler. It:
1) Acts as a lubricant for the water pump.
2) Helps protect the hoses from the inside (BTW, save your used coolant for wiping down your tires! It will restore the "new tire" look, rather than the "glazed donut" look you get with aftermarket tire dressings).
3) Helps reduce the electrolysis that naturally occurs in cooling systems that deteriorates metal.
4) Lowers the freezing point of the cooling system mixture
5) Raises the boiling point of the cooling system mixture.
This last one is the most deceptive. A cooling system in proper working order is a sealed system. That means that no outside air can get in, and as the temp rises, the system becomes pressurized. Pressure, combined with no added air, will keep the system from boiling under normal circumstances. By raising the boiling point, coolant actually raises the cooling mixture temp. The info on the sides of the coolant containers brag about being able to reach 260 degrees before boiling over, but guess what: DAMAGE CAN OCCUR AT OR BELOW 260 DEGREES!!! You want it to boil over before it gets that hot! That way you will stop driving, and let the system cool down. Coolant also retains heat, which makes it harder for the cooling system to dissipate the heat, like it's supposed to. Here in California, I never use more than 10% coolant, even when I go to the snow in the mountains. I worked for Bill Elliott in 1998, and was shocked to discover that those cars, with their 900 horsepower engines that drove for 500 miles straight, averaging 7000+ rpms, ran with 100% water in the cooling system. The only thing they use coolant for in NASCAR is to measure the cc's of the combustion chambers in their heads. Because they don't use coolant, they have to use a higher pressure rated radiator cap (28 - 30 psi), but since everything is new, it can easily handle that much pressure. Don't believe the hype: coolant actually makes your engine run hotter!

Here, this says it best...

From the Red Line Oil website:

THERMAL PROPERTIES
Water has amazingly superior heat transfer properties compared to virtually any other liquid cooling medium - far superior to glycol-based coolants. Water has almost 2.5 times greater thermal conductivity compared to glycol coolants. Mixtures of glycol and water have nearly proportional improvement due to the addition of water. Most heat is transferred in a cooling system by convection from hot metal to a cooler liquid as in the engine block or from a hot liquid to cooler metal surfaces, as in the radiator. The convection coefficient of liquids in a tube is a complicated relationship between the thermal conductivity, viscosity of the liquid, and the tube diameter which determines the amount of turbulent flow. Since 50/50 glycol solution has about 4 times the viscosity and only 70% of the thermal conductivity of water, the thermal convection coefficient for a 50/50 glycol solution is approximately 50% of the coefficient for water. Water in the cooling system is capable of transferring twice as much heat out of the same system as compared to a 50/50 glycol coolant and water solution. In order for a 50/50 glycol mixture to reject as much heat as water (amount of heat rejected is independent of the coolant), the temperature differentials at the heat transfer surface must be twice as great, which means higher cylinder head temperatures.

COOLANT EFFECTS ON PERFORMANCE
Under moderate load conditions, each percent glycol raises cylinder head temperatures by 1°F. 50% glycol raises head temperatures by 45°F. This increase in temperature will raise the octane required for trace knock levels by typically 3.5 octane numbers. A car equipped with a knock sensor will retard the timing to compensate for the increase in octane requirement by approximately 5°, which will reduce the maximum brake torque by about 2.1%. Racing vehicles not equipped with knock sensors can advance timing for increased torque.

For maximum temperature reductions use the most water and the least antifreeze possible to prevent freezing in your climate.

Take care,
~Chris

[twilightcall]

Chris thanks for the Great info. Very informative. I live in Southern TN. Would 20% coolant work even in the winter time down here. It can get down to 0 deg. but rarely does. It mostly gets down to 20-30's. Just wondering if I would need to add more coolant for the winter? Thanks.

[Evil Joe]

Thanks for all the responses...let me give you answer your questions an give you an update.

1.) My shroud and fan are in good shape. The fan clutch is the original, but it seems fine. There are no leaks and slight resistance is felt when I manually turn it. I was under the impression that a fan clutch only rarely contributes to overheating problems and when they do happen, they generally occur at low speeds.

2.) The "burping" procedure I posted always seemed a bit bogus to me as well, but I did it anyways. (I read it somewhere...) I think the idea is to make the radiator the highest point in the engine (to encourage bubbles to leave), but even when I lift the car, the tube that connects the thermostat to the radiator still is still king of the hill. Regardless, I usually squish that tube to help purge any air bubbles.

3.) I live in Los Angeles - so heat is definitely a concern. For the reasons listed by Chris, I always try to run as much water as possible. I leave a little coolant in there for lubrication. I've tried water wetter and it doesn't seem to make any difference. :-(


Anyways, here's an update:

I tested the guage using 10 ohm and 75 ohm resistors. It works fine. I also hooked up another guage (from another 5.0) to the car and it reads within 3-5 degrees of my instrument cluster. I also took some resistance measurements across the temperature sending unit:

210 F = 30 ohms
200 F = 35 ohms

Can someone please check what numbers they get at like 180 F and 195 F?

Thanks,
Joe

[Mach 1]

Originally posted by twilightcall
Chris thanks for the Great info. Very informative. I live in Southern TN. Would 20% coolant work even in the winter time down here. It can get down to 0 deg. but rarely does. It mostly gets down to 20-30's. Just wondering if I would need to add more coolant for the winter? Thanks.

You can buy a tester tube that you suck up some of your mixture and it tells you what temperature you are protected to. Any auto parts store or wally world has them too..it has balls that float and coresponds to mixture level and temp. of freezing.

[Hozer 88GTConv]

Since you have done everything else, I would swap the fan clutch out. A bad clutch is hard to diagnose sometimes just by feel.

Anyway, it's cheap and quick.

[PKRWUD]

Originally posted by twilightcall
Chris thanks for the Great info. Very informative. I live in Southern TN. Would 20% coolant work even in the winter time down here. It can get down to 0 deg. but rarely does. It mostly gets down to 20-30's. Just wondering if I would need to add more coolant for the winter? Thanks.

I'd go with 20% coolant until the time of year when the weather stays at freezing for more than an hour at a time, and then drain off half a gallon from the drain, and add a half gallon of coolant.

Take care,
~Chris

[PKRWUD]

I agree with replacing the fan clutch.

Take care,
~Chris