View Full Version : Cobra's gettin hot

03-15-2007, 12:14 PM
Hello all,
Just bought a 98 Cobra which I took some great advice from people on this website, thank you very much. Anyway I got a great deal on the car (should I buy it forum) because it had a few problems with the motor. One of the problems is the car gets hot and blows no heat. I noticed when it's hot, the fan is not working. Of course the car came with no owners manual so without going out and buying a tech manual or something, I'm lost as to which relay controls the fan. Are there any experienced Cobra owners have any advise for me?

03-16-2007, 06:42 AM
I am not sure which relay or fuse may be the culprit for the fan not working (should be in power distribution box).

However, if there is not heat from the heater, the car gets soaking hot, fan does not come on, this would make me think that
1. water pump is not moving coolant (this would make noise so I doupt it)
2. Thermostat is missing or not functional.
3. there is no coolant in the cooling system.
4. coolant is low and there is alot of air in the system.

If the temperature sending uint that controls the fan is not immersed in coolant, it will read lower temperatures and not turn on the fan circuit.
You may need to bleed the cooling system to get any air out.

If the cooling system is purged of air and in good shape. Check the wire connections to the temperature sending units. (there should be two, one for the temp guage, and the other for the PCM ) Bad connections will result in low temperature readings which will prevent the fan from turning on. Also the heater core may have a temperature sensitive actuator (I doupt it, this is why I suggested checking fluid levels ). Heater has a pneumatic actuator controlled by engine vacuum, either the actuator is bad or the vacuum line is damaged or unconnected.

03-16-2007, 07:14 AM
First make sure you have plenty of coolent and no air in the system. On the 96-98 Cobras you MUST burp the cooling system to prevent air lock and over heating. The black crossover tube (center top of the engine in front of the altenator) has a plug that uses a 3/8s drive to open. You need to open there and add coolent/water till it is completely full then close, start the engine let it come to temp, shutdown, cool off and repeat. After the second time you should have the air out of the system.

After you make sure the air is out and you have plenty of coolent then Ausie has the right list to check.:thumbsup:

03-19-2007, 01:48 PM
Thanks for all the advice everyone, it was a big help!! I replaced the thermostat, then realized the fan was not coming on. Once I fixed the fan, I thought I was good to go. I let the car idle in my driveway for about 45 minutes, and the temp was right in the middle. I started driving it, and took it on the freeway and then the temp started to climb all the way to the L in normal on the temp gauge. I was pretty upset and parked it for the night. I think I might have a blown head gasket, or maybe a bum waterpump. I don't have any anti freeze in the oil, or no white smoke out the exhaust, but something is up. I think a pretty good sign is to start the car and run it until the thermostat opens up and then see if I can take the radiator cap off. If it boils over like a volcano, I'm getting pressure from somewhere, probably the head. Anyway, I just wanted to say thanks.

03-19-2007, 07:38 PM
If you have a blown head gasket, look for air bubbles in the radiator or water in the oil.

03-19-2007, 09:45 PM
One thing that I did not see anybody mention yet is the possibility that your radiator could be to blame. I had an '85 GT that acted a lot like what you have described. I eliminated most of the cooling system components as the culprit either through testing or replacement. The fan was working (old school clutch fan), the thermostat was replaced (and later even temporarily removed), there was no air in the system, the water pump was OK (water pumps are very rarely to blame anyhow), head gaskets were not blown. My car would also seem to do fine at idle until I drove it. It turned out that several of the bottom most rows of my radiator were plugged up. I took the radiator to a shop to be cleaned out and the cooling problems went away. This is just one more thing you might want to consider. Hope you find the problem.


I forgot - the one differnce was that my car did have adequate output from the heater. But, if the radiator could be plugged, it is not impossible that the heater core could be too.

03-20-2007, 07:30 AM
I would agree with George on that.... Once deposits take over in the radiator, the cooling efficiency drops considerably. Deposits with an aluminum block are not as sever as they tend to be with a cast iron block. Mostly Calcium deposits and some other stuff. Iron blocks tend to load the radiator with rust. Also the channels in the heads will also form deposits which will block off the cooling passages. One of the issues is the cooling system itself. Once you get trapped air into the system it will not function properly. Air typically gets trapped in the block. As mentioned by Hazman, purging the cooling system is very important to removing the air out of the heads and cooling system. The bleed port on the crossover tube is the key to removing air from the cooling system.

Boilovers could be a result of exhaust gasses in the cooling system which would be obvious there is a head gasket issue. If you were burning coolant in the cylinders, the spark plug would come out either rusty or very clean with little or no deposits on them. However, coolant may not be getting into the cylinder at all. In other words, exhaust gasses and or fuel from compression would enter the cooling system if the head gaskets have a weak spot. You could probalby have a leak down or compression test performed to determine if it is a head gasket issue. Foam or bubbles in the coolant :thumbsup: especially at the bottom of the resivior cap is an indication of a possible severe problem.

If you do get boilovers, it could be a result of loss of pressure from the cap or a leak.

I would agree with George that water pumps do not fail as common but once they do you would know it since they tend to make noise or spew coolant out through the weep hole that is on the pump (or begin to leak at the pump gasket). I would at least inspect the water pump for signs of leakage.

The worse thing that one could do is to use one of the chemicals (block repair or radiator sealer) to fix a cooling issue since that will cause more damage than the leak itself.

If it turns out to be a head gasket, take advantage of that and have the heads cleaned and checked (valve guides, springs, seats, etc....)

03-20-2007, 09:57 AM
Thanks alot everyone. I really appreciate everyone's help. I guess I should mention that after putting the termostat in, now I have heat. Really, the only problem now is the overheating. Last night I drove it around a while and brought it up to temperature and took the radiator cap off and had no coolant come out of the bottle. I then drove it around some more, the temp stayed in the middle, then I took the cap off again and had a lot of coolant come out of the bottle, so I parked it. I think I'll take the advice and have the radiator checked. That's something I can do this weekend maybe. Again, thanks for all the advice.

03-21-2007, 07:13 AM
The way it sounds as if you still have trapped air in the cooling system. Once you remove coolant from the system (replacing thermostat) you have to purge the cooling system of trapped air. There should be a bleed port on the cross over tube (round with a 1/4 inch square notch in it). A quarter inch drive with an extention is all you need to remove it (do not use the end of the socket wrench directly since it is of harder steel and has that slip lock ball in it that would cause the square to round out easily). Once you have the bleed port open, this is where you add coolant (use a small funnel). If the coolant level (when cold) in the expansion tank (what you refer to as the bottle) is low, just remove the cap and fill from the bleed port only. When the level in the bottle is beginning to overflow, put the cap back on. Squeeze the main radiator hose slowly a few times since this will help push out some air. Continue to fill at the bleed port until it you can no longer add coolant. Also if you have to mix coolant with water best to use distilled bottled water and not tap water. Close up the bleed port but do not make it tight (just snug). Set the heater to full hot, fan speed will not matter, and turn on the heat (set to floor or vent) to actuate the vacuum solenoid to get heat. Start the car and allow to warm up to operating temperature (watch the temp guage and see where it gets too) Once the fan cycles on which is when the thermostat opens, you can either wait for the fan to turn off or just shut off the engine. Let it cool down for an hour or two. Release any pressure in the expansion tank by opening the cap on the expansion tank (bottle). If the cooling system is cool enough, open up the bleed port again and add more coolant there. Close the cap when the expansion tank begins to overflow. Squeeze the main hoses again. Add coolant if needed and then close up the bleed port just tight enough but do not over torque it. restart the engine with the heater on, Run the engine through one fan cycle and shut down. Let the engine cool down and check the coolant level on the expanstion tank (bottle). Add coolant to the expansion tank if the level is low.

The trick is to get the air out of the heads and block. The expansion tank or plastic bottle with the bubbled black top often refered to as the resivior, is designed to have an air pocket at the top which is there to allow for expansion of the coolant at higher temperatures. If the coolant system is not purged of air properly, it will mimic symtoms of a head gasket failure, overheat and spew coolant from the expansion tank since the air and coolant residing in the block becomes super heated.

If purging the cooling system does not cure the issue, then it may be blockage in the radiator or else where. Also if you have an abundance of overflows spewing out from the cap that could be an sign of head gasket trauma. Note, after purging the cooling system, there may be a chance of one overflow occuring if the system has too much coolant in it. After the last heat cycle and cool down, if the level is a bit high in the expansion tank, I usually remove some coolant before driving it. Always recheck the level after a few road trips. If it drops add coolant to the expansion tank. If you notice a considerable loss of coolant but have no signs of a leak that would be another indicaiton of head gasket failure, either that, or the leak is in a location other than the obvious, freezeout plug, heater line leak, or one of the block coolant plugs is leaking (alternate means of draining the block of coolant but not sure where they are located).

04-04-2007, 03:27 PM
Thanks for all the support. I did everything and it still was getting hot, so I took it to my mechanic who put it on the computer and told me that the right side bank was trying to get a lot more fuel than the left side. This told him water is getting burned off in the cylinder walls which meant a blown head gasket. He quoted $1,700 to pull them off and replace the valves. Others have told me that this is a pretty good price, but it is still $1,700. I'm no mechanic for sure, but I've pulled heads off a few times, but nothing like this. Is this a "let the professional handle it" job, or something I can tackle?

04-04-2007, 06:08 PM
Personally, I would not be convinced that you have a head gasket problem without a leakdown test, or at the very least pulling the plugs to see if any of them show signs of coolant in the cylinder, especially since you mentioned that you are not seeing any white smoke and there is no evidence of coolant in the oil. Are you losing coolant? And, why did your mechanic say he would have to replace the valves? If the heads need pulled, I would do a valve job, but not necessarily replace the valves unless some are damaged. You could possibly have a bad head gasket, I would just want to be sure before spending the money.

Hope you get to the bottom of it.

04-05-2007, 08:12 AM
Personally, I would not be convinced that you have a head gasket problem without a leakdown test, or at the very least pulling the plugs to see if any of them show signs of coolant in the cylinder, especially since you mentioned that you are not seeing any white smoke and there is no evidence of coolant in the oil. Are you losing coolant? And, why did your mechanic say he would have to replace the valves? If the heads need pulled, I would do a valve job, but not necessarily replace the valves unless some are damaged. You could possibly have a bad head gasket, I would just want to be sure before spending the money.

Hope you get to the bottom of it.
I agree with this statement, even though computers are a big help in diagnosing problems, there's nothing like seeing it first hand. I would do exactly like above, check the plugs, do a leakdown, then you'll know where you stand. $1700 is not a bad price to pull the heads/replace the valves.

04-06-2007, 07:02 AM
From what I recall, there are two temperature sensors, one is only for the temp guage and the other is to monitor engine temperature. Both are tied into the cooling system as a means to measure the temperature of the engine coolant as a representation of engine temperature. The only components that regulate fuel delivery per bank are the O2 sensors. If one bank becomes slow and sluggish it will increase fuel ratio on that bank. My thoughts on this could point to one of the O2 sensors was replaced while the other was left intact. Keep in mind that coolant will damage an O2 sensor over time (as well as oil, etc...). The O2 sensors can be tested electronically through the ODBII port by performing an emmisions test or using a scan tool that has the ability to test the emmisions components. If the O2 sensors check out fine, there may be a header leak on one side or damage such as a crack or hole on one of the headers that could create the difference in fuel per bank if the O2 sensor is influenced by the defect in the header.
The head gaskets could be in good shape and if there is a coolant leak it may be a result of a cracked head casting or defect. If you did have a blown head gasket, you would find a few floaters in the coolant floating in the expansion tank. Could be oil droplets, or grey or black colored globs. You may not necessarily find coolant in the oil. Look at the underside of the oil fill cap for evidence of coolant in the oil since it will condensate on the bottom side of the cap. If you find it on the dip stick then you have a problem since water will displace oil and stay on the bottom of the oil pan.

A compression test will rule out head gasket or valve issues as well as a leak down test. If testing does not prove a problem with the engine, the issue is external (headers, O2 sensors, injectors, fuel rail issues). Running lean will increase temperatures as well as increase potential for detonation, rich conditions will eventually lead to the same hot motor if the fuel ratio is rich enough to remove the oil film on the cylinder wall.

Also note: if the engine is running really hot, some of the superheated coolant will displace the fluids in the cooling system which will make it appear there is a head gasket fault since you may get some boil overs or coolant escaping from the filler cap. Once you start boiling the coolant, the pressure will increase in the cooling system and blow off the cap. This could happen if there is trapped air in the cooling system.

Before you tear into head removal, at least test compression and or have a leak down test performed. That could save you $1700 in repair if it is not needed.