Heat swings
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Senior Member
Joined: May 2000
Posts: 1,317
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From: Virginia Beach, VA
Heat swings
Just looking for input on potential causes. I am getting temp swings, but within the normal range.
I used to get a much smaller swing when under heavy load at lower speeds. Recently I had a radiator tank leak, and had it repaired. After putting it back in I noticed the larger swing. Made sure it had "burbed" all the air out and it wasn't making the water pump cavitate. I backflushed the system when I put the new rad in, and nothing wrong. The old antifreeze looked good, and I have no reason to belive there are any clogged passages in the rad or the engine.
Being it was cheap quick and good preventative maintenance anyway I went ahead and stuck a new thermostat in. No apparent change.
I haven't actually tested the temp sender yet, but the move is smooth and the gauge appears to be working. I plan on testing both that and the fan clutch today if I have time, just looking for other possiblities while I'm at it. I also planned on checking for codes in case the EGR was acting up, or anything else that might affect the temp. The water pump has no play, is making no noise, and not weeping. During the back flush it seemed to be pumping fine.
It appears that the engine isn't producing excessive heat, but that the cooling system is simply responding slow to load and heat changes. I had initially ruled out the fan clutch suspecting the stat was sticking and since my oil cooler makes it hard to cover the front end to block flow.
I am still concerned as I didn't think the fan clutch responded so quickly to temp changes, but maybe that thing responds quicker than I thought.
Like I said, it's never going out of normal range, but seems to be waving more rather than it's usual more stable state.
I've been considering electrics but want to get this figured out before I do, even if it means buying parts that will soon be replaced. Any further thoughts appreciated.
I used to get a much smaller swing when under heavy load at lower speeds. Recently I had a radiator tank leak, and had it repaired. After putting it back in I noticed the larger swing. Made sure it had "burbed" all the air out and it wasn't making the water pump cavitate. I backflushed the system when I put the new rad in, and nothing wrong. The old antifreeze looked good, and I have no reason to belive there are any clogged passages in the rad or the engine.
Being it was cheap quick and good preventative maintenance anyway I went ahead and stuck a new thermostat in. No apparent change.
I haven't actually tested the temp sender yet, but the move is smooth and the gauge appears to be working. I plan on testing both that and the fan clutch today if I have time, just looking for other possiblities while I'm at it. I also planned on checking for codes in case the EGR was acting up, or anything else that might affect the temp. The water pump has no play, is making no noise, and not weeping. During the back flush it seemed to be pumping fine.
It appears that the engine isn't producing excessive heat, but that the cooling system is simply responding slow to load and heat changes. I had initially ruled out the fan clutch suspecting the stat was sticking and since my oil cooler makes it hard to cover the front end to block flow.
I am still concerned as I didn't think the fan clutch responded so quickly to temp changes, but maybe that thing responds quicker than I thought.Like I said, it's never going out of normal range, but seems to be waving more rather than it's usual more stable state.
I've been considering electrics but want to get this figured out before I do, even if it means buying parts that will soon be replaced. Any further thoughts appreciated.
Thread Starter
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Senior Member
Joined: May 2000
Posts: 1,317
Likes: 0
From: Virginia Beach, VA
The fan clutch was WAY BEYOND gone. The first couple of days I never had a chance to really check it other than to give it a spin to check for resistance.
I finally caught the truck fully cooled down and checked it, it was completely free wheeling. As a note it did have normal resistance if you turned the fan. After taking it out I found that the resistance was normal for about 12-15 turns, then would slack off a little bit. After a few more turns... maybe 20-25 total it may has well have just been a bearing with no resistance at all.
I'll post more later when I have time, as this has opened my eyes to just how good the factory cooling system is.
F150 freak,
If you need any help checking your clutch let us know, it's a very easy procudure. I'm short on time or I would post it now.... maybe later just in case you need it....
I finally caught the truck fully cooled down and checked it, it was completely free wheeling. As a note it did have normal resistance if you turned the fan. After taking it out I found that the resistance was normal for about 12-15 turns, then would slack off a little bit. After a few more turns... maybe 20-25 total it may has well have just been a bearing with no resistance at all.
I'll post more later when I have time, as this has opened my eyes to just how good the factory cooling system is.
F150 freak,
If you need any help checking your clutch let us know, it's a very easy procudure. I'm short on time or I would post it now.... maybe later just in case you need it....
Senior Member
Joined: Nov 2002
Posts: 439
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From: Somewhere Down South
Mine started that crap at about 200,000 miles, I looked for weeks and was told to install a flush kit, bout $8. Man you wouldn't believe the #%$# that came outta my cooling system. Never saw another temp swing til the water pump quit at 250,000.
You should seriously try the flush if you haven't already.
You should seriously try the flush if you haven't already.
Thread Starter
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Senior Member
Joined: May 2000
Posts: 1,317
Likes: 0
From: Virginia Beach, VA
ccnseven,
I did do the flush, and I agree those kits are money well spent. My system was still quite clean considering the truck is approaching 100K miles. I wish I could find the connector from my old flush kit.... years ago they didn't have the "backflow preventer" in them. I had a kit put thought I had used the proper T fitting on my old truck. After buying a new T and clamps at AutoZone I found that I had the one I needed with the kit anyway. Oh well, at least I know I have all the sizes so I can put one on the wifes car.
As it turned out the fan clutch was completely gone, and my truck had more or less been operating without a fan during that time frame.
Lessons learned.....
1. The factory cooling system is WAY more efficient than I had thought. Even with my underdrive pulleys the system was keeping the truck within the "normal" range even with the fan clutch not working.
2. When I did the 'stat all the local parts places listed a 197 degree stat as the stock temp. When I pulled the old one out it was a 192. My truck has the tranny cooler and from what I can find the "super cooling package". It could be that this package included a slightly cooler stat.
3. The factory fan clutch is a BIG unit. I didn't have time to play games so I picked up the Hayden extreme duty unit they had in stock, and it was smaller than the factory unit.
4. You CAN replace the fan clutch without removing the shroud. I always wondered why a 7 bladed fan had unequal spacing between the blades, but now I think I know why.
5. At the advice of the radiator guy, I am replacing the stock pressure cap with a 7 lb unit. He says that the newer hotter running vehicles tend to eat seals quicker, and that the stock cap is way to much. Doing the math I found that with the stocker on the boil over point would be about 259 degrees. This is the natural boiling point of 212, plus roughly 8 for a 50/50 mixture of anit-freeze/coolant, plus 3 degrees per pound of pressure, and the stocker is 13 lbs. Going to the 7 lb cap brings it down to the 241 range.
My seal went right around the input side. From their experience the hot water at shutoff sits on that side of that tank. Lowering the cap pressure allows some to blow off if you shut the truck off hot which also helps move the hot spot into the rad some, and away from the tank.
The other logic is that 260 is just too hot.... better to boil over and be forced to shut down rather than risk forcing engine damage by letting the temp get way up.
These guys had a lot of experience with stock, custom and race stuff, so I took their advice.
6. After seeing it first hand, I am quite sure a single electric mounted in place of the stock fan would cool these trucks quite well. Once again I asked and was told that most electrics even with a shroud allow hot spots in the rad due to the "flat" shroud not pulling air evenly. I made a call to a buddy and he took some readings off his radiator... hot spots. I am convinced that a large shroud and single large fan is the way to go now.
Rant mode off!
I am having a problem getting the last little "burp" out of the system for some reason. Under high revs I can hear a slight "gurgle" of water hitting the heater core, so apparently I still have a pocket of air in there somewhere.
Other than that, the temp is slightly higher due to the stat but I will leave it in. Rock solid with the new stat and fan clutch in place, and the swing I had is now back to the very small move it used to be.
OOps.. rant mode back on!
Just an observation. The flow from a stock fan brought the underhood temps WAY down at idle. Common logic would suggest that electrics would allow the IAT and MAF to get heat soaked much quicker for anyone running an open element with electrics. On my truck I swiss cheesed the stock box but kept the factory cool air tube. Even at idle it does pull some air. I left it off during the work/troubleshooting, and got a very slight ping under full throttle. With the tube back on, no ping. Cool air is the ticket and I am now pondering a higher flowing sealed system that isolates the intake from the engine compartment even more if possible.
Rant mode back off... really!
I did do the flush, and I agree those kits are money well spent. My system was still quite clean considering the truck is approaching 100K miles. I wish I could find the connector from my old flush kit.... years ago they didn't have the "backflow preventer" in them. I had a kit put thought I had used the proper T fitting on my old truck. After buying a new T and clamps at AutoZone I found that I had the one I needed with the kit anyway. Oh well, at least I know I have all the sizes so I can put one on the wifes car.
As it turned out the fan clutch was completely gone, and my truck had more or less been operating without a fan during that time frame.
Lessons learned.....
1. The factory cooling system is WAY more efficient than I had thought. Even with my underdrive pulleys the system was keeping the truck within the "normal" range even with the fan clutch not working.
2. When I did the 'stat all the local parts places listed a 197 degree stat as the stock temp. When I pulled the old one out it was a 192. My truck has the tranny cooler and from what I can find the "super cooling package". It could be that this package included a slightly cooler stat.
3. The factory fan clutch is a BIG unit. I didn't have time to play games so I picked up the Hayden extreme duty unit they had in stock, and it was smaller than the factory unit.
4. You CAN replace the fan clutch without removing the shroud. I always wondered why a 7 bladed fan had unequal spacing between the blades, but now I think I know why.
5. At the advice of the radiator guy, I am replacing the stock pressure cap with a 7 lb unit. He says that the newer hotter running vehicles tend to eat seals quicker, and that the stock cap is way to much. Doing the math I found that with the stocker on the boil over point would be about 259 degrees. This is the natural boiling point of 212, plus roughly 8 for a 50/50 mixture of anit-freeze/coolant, plus 3 degrees per pound of pressure, and the stocker is 13 lbs. Going to the 7 lb cap brings it down to the 241 range.
My seal went right around the input side. From their experience the hot water at shutoff sits on that side of that tank. Lowering the cap pressure allows some to blow off if you shut the truck off hot which also helps move the hot spot into the rad some, and away from the tank.
The other logic is that 260 is just too hot.... better to boil over and be forced to shut down rather than risk forcing engine damage by letting the temp get way up.
These guys had a lot of experience with stock, custom and race stuff, so I took their advice.
6. After seeing it first hand, I am quite sure a single electric mounted in place of the stock fan would cool these trucks quite well. Once again I asked and was told that most electrics even with a shroud allow hot spots in the rad due to the "flat" shroud not pulling air evenly. I made a call to a buddy and he took some readings off his radiator... hot spots. I am convinced that a large shroud and single large fan is the way to go now.
Rant mode off!
I am having a problem getting the last little "burp" out of the system for some reason. Under high revs I can hear a slight "gurgle" of water hitting the heater core, so apparently I still have a pocket of air in there somewhere.
Other than that, the temp is slightly higher due to the stat but I will leave it in. Rock solid with the new stat and fan clutch in place, and the swing I had is now back to the very small move it used to be.
OOps.. rant mode back on!
Just an observation. The flow from a stock fan brought the underhood temps WAY down at idle. Common logic would suggest that electrics would allow the IAT and MAF to get heat soaked much quicker for anyone running an open element with electrics. On my truck I swiss cheesed the stock box but kept the factory cool air tube. Even at idle it does pull some air. I left it off during the work/troubleshooting, and got a very slight ping under full throttle. With the tube back on, no ping. Cool air is the ticket and I am now pondering a higher flowing sealed system that isolates the intake from the engine compartment even more if possible.
Rant mode back off... really!