Radiator/ Heating Problems
11-26-2007, 02:47 AM
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Radiator/ Heating Problems
98 f150 v8 4.6L
Recently I've been getting fluctuating temperture readings from the temp gauge on the dash and my heat would go cold after the truck had been running for a while on the highway. The temp guage would go from normal temp to cold and then suddenly hot! and then back to normal temp. So I flushed the system with prestone super flush and changed the thermostat and replaced the radiator cap. I still have the same symptoms as before except now radiator fliud likes to spill/shoot out of the cap I just bought. I have tried the old cap and it does the same thing. It doesn't seem to shoot radiatior fluid out after it does it the first time when I refill it. Also, one other symptom I forgot to mention, even though the temp guage reads normal, the heat coming through into the cab turns to cool. It seems after i give it a little gas that it comes back on again. I'm thinking now that it's the water pump but I looked in the service manual and it says the water pump is good if there is no anifreeze coming out of some sort of spout either on top or bottom of it and it isn't. So what's happening here?
Recently I've been getting fluctuating temperture readings from the temp gauge on the dash and my heat would go cold after the truck had been running for a while on the highway. The temp guage would go from normal temp to cold and then suddenly hot! and then back to normal temp. So I flushed the system with prestone super flush and changed the thermostat and replaced the radiator cap. I still have the same symptoms as before except now radiator fliud likes to spill/shoot out of the cap I just bought. I have tried the old cap and it does the same thing. It doesn't seem to shoot radiatior fluid out after it does it the first time when I refill it. Also, one other symptom I forgot to mention, even though the temp guage reads normal, the heat coming through into the cab turns to cool. It seems after i give it a little gas that it comes back on again. I'm thinking now that it's the water pump but I looked in the service manual and it says the water pump is good if there is no anifreeze coming out of some sort of spout either on top or bottom of it and it isn't. So what's happening here?
11-26-2007, 07:54 AM
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One of the typical failures of the water pump involves the seal. There is a weep-hole on the pump which indicates a seal problem when coolant leaks out.
The things to consider checking:
Is the thermostat put in the correct way? The spring should be pointed in toward the engine. The previous thermostat could have just stopped working for its failure mode.
The spewing cap thing is a concern, but may be a result of other issues, especially since two different caps behave the same way.
The erratic heater operation and the wildly swinging temperature indications sounds a bit like there is air entrapped in the system.
I suppose it could be the water pump, but impeller failures are pretty rare.
The things to consider checking:
Is the thermostat put in the correct way? The spring should be pointed in toward the engine. The previous thermostat could have just stopped working for its failure mode.
The spewing cap thing is a concern, but may be a result of other issues, especially since two different caps behave the same way.
The erratic heater operation and the wildly swinging temperature indications sounds a bit like there is air entrapped in the system.
I suppose it could be the water pump, but impeller failures are pretty rare.
12-01-2007, 08:21 PM
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I checked the thermostat and it was in the correct way and while I was at it I put a new lower hose and upper hose on and also took the raditor and pressured washed it and got rid of all the dirt. When I had the raditor out I didn't notice antifreeze/leaks anywhere. The raditor looked pretty much like new. After accomplishing all that I took it out for a test drive and it did its thing again... warm up, cool down, over heat - except this time it didn't go back to normal again and the check engine light came on. so i pulled over and turned the truck off. about 5 secs later I turned it back on and it was back to normal temp but the engine light is still on. What do you think it could be? And if it is air entrapped in the system, how can it get in there in the first place?
Last edited by czecher01; 12-01-2007 at 09:28 PM. Reason: needed to add more
12-02-2007, 12:29 AM
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Is the truck really overheating, or is the sending unit/gauge acting up? When is the coolant spewing out the radiator filler neck? Does it do it if you take the cap off while the engine is hot?? (Heaven forbid. It should never be removed when hot). Does it do it from a cold start just before the t-stat opens? Does the engine knock when the gauge is showing hot?
There might be an air pocket in the system, or the sending unit/gauge may be bad. You need to find out if it is really overheating or not. The check engine light will come on if the sending unit is giving false info to the computer.
Good luck and let us know what you find out.
Dan Harriman 84 F150 lwb
Orange, Texas
There might be an air pocket in the system, or the sending unit/gauge may be bad. You need to find out if it is really overheating or not. The check engine light will come on if the sending unit is giving false info to the computer.
Good luck and let us know what you find out.
Dan Harriman 84 F150 lwb
Orange, Texas
12-02-2007, 08:34 AM
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The sending unit cannot be bad because after it warms up and then goes back to cool, the heat coming into the truck goes from warm to cool as well.
I thought about the sending unit to be bad but with the spewing going on... there's got to be something else going on.
It'll over flow if I take the cap off while it's hot. Not sure when the fluid spews out but my guess is when it over heats and returns to normal temp because that's when the air pocket is being pushed out.
When it's overheated and the engine light comes on it won't let me accelerate. Just kinda rumbles a little bit when I hit the gas.
Remember, it only spews after I refill the tank. Now it doesn't seem to need it anyways so the spewing seems to be minimal. After I've been driving around for about 30 minutes and I get out of the truck. I can smell the antifreeze. Not an overwhelming smell but I can smell it. If I look under the hood and it hasn't spewed, I don't notice any leaks. I've looked high and low and I just can't find anything. Any other suggestions?
I thought about the sending unit to be bad but with the spewing going on... there's got to be something else going on.
It'll over flow if I take the cap off while it's hot. Not sure when the fluid spews out but my guess is when it over heats and returns to normal temp because that's when the air pocket is being pushed out.
When it's overheated and the engine light comes on it won't let me accelerate. Just kinda rumbles a little bit when I hit the gas.
Remember, it only spews after I refill the tank. Now it doesn't seem to need it anyways so the spewing seems to be minimal. After I've been driving around for about 30 minutes and I get out of the truck. I can smell the antifreeze. Not an overwhelming smell but I can smell it. If I look under the hood and it hasn't spewed, I don't notice any leaks. I've looked high and low and I just can't find anything. Any other suggestions?
Last edited by czecher01; 12-02-2007 at 11:06 AM. Reason: Correct statement
12-02-2007, 06:58 PM
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Well I replaced the raditor with a new one. Still the same effect. Can I count on it being the water pump?
One thing concerning the thermostat. Is the o-ring suppose to go in 1st and then the thermostat or the other way around??
One thing concerning the thermostat. Is the o-ring suppose to go in 1st and then the thermostat or the other way around??
Last edited by czecher01; 12-02-2007 at 07:07 PM.
12-02-2007, 07:44 PM
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Well, that answered one thought I had - about the radiator being plugged internally.
It sounds like the water isn't circulating very well. There's either a flow obstruction (such as the prior suggestions of the thermostat or radiator), or the coolant-mover simply ain't moving coolant.
Not sure about the o-ring, but it may be something to consider that if it were installed wrong, it may have interfered with thermostat operation. I would take a WAG and say that the thermostat should go in first - like with the conventional gaskets - thermostat in, gasket over the top.
The warm, then cool, then overheat sequence still has me puzzled - if the pump weren't working, don't understand the intermediate 'cool' part.
Once the thermostat installation issue is resolved, and the overheating hasn't been solved, it may then be worthwhile to pull the pump to have a look. If one can't figure out what it is, then start eliminating the things it's not.
Ah, and BTW - air can get into the system whenever the system is drained. For example, the heater core hoses drain, but are still higher than the radiator fill neck. Any relative high spot, including the upper radiator hose, will hold air until coolant is pushed through and the air eventually is pushed out through the radiator cap.
Also, another thought, if you should have a head gasket leak, could be getting air into the system that way, if the stars align right. Your comment about smelling coolant has me wondering a bit.
Perhaps when you refill the radiator, allow it to warm up at idle speed until the thermostat opens. Any significant air quantities should be relieved, then the cap can be put on.
It sounds like the water isn't circulating very well. There's either a flow obstruction (such as the prior suggestions of the thermostat or radiator), or the coolant-mover simply ain't moving coolant.
Not sure about the o-ring, but it may be something to consider that if it were installed wrong, it may have interfered with thermostat operation. I would take a WAG and say that the thermostat should go in first - like with the conventional gaskets - thermostat in, gasket over the top.
The warm, then cool, then overheat sequence still has me puzzled - if the pump weren't working, don't understand the intermediate 'cool' part.
Once the thermostat installation issue is resolved, and the overheating hasn't been solved, it may then be worthwhile to pull the pump to have a look. If one can't figure out what it is, then start eliminating the things it's not.
Ah, and BTW - air can get into the system whenever the system is drained. For example, the heater core hoses drain, but are still higher than the radiator fill neck. Any relative high spot, including the upper radiator hose, will hold air until coolant is pushed through and the air eventually is pushed out through the radiator cap.
Also, another thought, if you should have a head gasket leak, could be getting air into the system that way, if the stars align right. Your comment about smelling coolant has me wondering a bit.
Perhaps when you refill the radiator, allow it to warm up at idle speed until the thermostat opens. Any significant air quantities should be relieved, then the cap can be put on.
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12-02-2007, 09:16 PM
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Just wanted to throw in with the exact same problem with my 97 4.6L and haven't been able to find an answer either. I can say I don't think the engine is really overheating, my gauge shoots up and drops really fast and when the fluid overflows, only when it is full, it is cool to the touch. Everything I have read is just like mine, I thought this info might help a little bit. Also, it goes thermostat then o-ring, I replaced mine as well and it didn't solve anything.
12-03-2007, 01:25 AM
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Thermostat then gasket is what I had the whole time. Just popped into my head today that maybe an issue.
Now that I really think about that anitfreeze smell after I've been driving for a while... I think it was just from spilling some myself or it could have been left over from the spewing.
I'll have to try unscrewing the cap and let the thermostat open and see what that does. I'm suspecting the water pump so I'll take that out and get a good look at it. Either way I think I'm going to replace it with a new one since I have it out. I'll have to wait till tomorrow to do that. Thanks everybody for your help so far! I'll keep you posted.