Background – the truck (1985 F150 with a 4.9L rebuilt 40,000 miles ago and a 4sp with od) was parked from June 2009 until January 2012 when I started getting it road worthy again. In January 2012, while letting it idle, I noticed the radiator was leaking where it meets the inlet end tank. That turned out to be a bad inlet end tank gasket. I replaced the gasket, cleaned the end tank, cleaned the radiator fins and ran water through the radiator using my garden hose then reinstalled everything. The temperature gauge read “normal” all the while. In May 2012 I replaced engine coolant temp sender because I broke the previous one while changing the intake and exhaust gasket. The temperature gauge still read “normal” all the while, although the gauge now read squarely between “O” and “R” where it had previously read between “N” and “O.” I do not take the stock gauge as gospel; rather, I take it as a general guideline of approximately how hot the engine is normally running. The truck had no fan shroud when I got it and it still does not have one.

Current Problem – A previous owner bypassed the heater core. I’m told the heater core was bad and needed to be replaced, which it allegedly was. Meanwhile, the heater core hoses were replaced with a bypass hose. The heater bypass hose sprung a leak this weekend and puked coolant all over like blood in a Quentin Terentino movie. An adjustment and tightening of the bypass hose resolved that problem. I put some water in the overflow tank and some in the radiator then let the truck idle until it was warm to see if the leak persisted. After 20 completely dry minutes (meaning no leaks) I concluded all was well. The temp gauge read normal until hit a drive thru, at which point the temp gauge read between the “M” and the “A” in “Normal,” but it returned to normal as soon as I pulled away.

I will top off the coolant before I drive home. I am not seeing any other leaks, but it has only been a few miles. Could the heater core being bypassed and/or a lack of a fan shroud be contributing to the unusually high temp while idling?

 

Before the initial post I did some research and I read that an air bubble could cause issues, so after posting I went out, opened the radiator cap, topped it off (which didn't take much) then I started the truck and let it idle until it was good and warmed up. The temp gauge climbed up to the "M" at which point I tapped the throttle, the coolant bubbled over the top of the radiator some then dipped and the gauge fell back down to the "R" where it normally runs when it's 95 degrees outside as it is today. I topped it off some more then drove a few miles to Mom's and all was well. Leaving Mom's to drive the 5 miles home, I got about a mile away and while stopped at a stop light the gauge climbed up between "M" and "A" again. I tapped the throttle and the gauge fell back down to "R" again. So my current questions are:

- does bypassing the heater change or impact the efficacy of the cooling system?
- how does the fan shroud impact efficacy?
- just to be thorough, how does one check the fan clutch?

 

that and fan clutch

 

Heater core being bypassed has no affect on the cooling system.

The fan shroud has a big affect on cooling when the truck is not moving. It makes the fan pull the air through the radiator, instead of around the sides of the fan.

The fan clutch also has a large affect on cooling when sitting. When it's hot as you say(if we can believe the gauge, I don't usually) and when you tap the throttle, you should hear quite a roar from underneath the hood. If not, it's probably not locking up as it should. If you see dirt around the clutch, the fluid has probably leaked out. You can also grab it and shake the fan and see how much play it has in the clutch. Any at all, and it's no good.

 

x2 on what Franklin said.

If you tap the throttle and the temp goes down, there's probably an air bubble somewhere in the system, as the increased flow pulls some of it out. I've had cars take a week or two of driving to finally get all the air out.

If you sit in traffic or do any amount of idling, you should really get a shroud on it. With a properly functioning cooling system, you should be able to start the engine and let it idle all day long without it overheating. Like my truck, the temp will climb to 195-200 and sit there no matter how long it's idling (I'll use it for light at times and don't want the battery draining).

I would say, just keep filling the overflow, not the radiator. As the system heats up, it will push out any air in it and as it cools, it will suck in coolant from the tank. You may also want to overfill the overflow a little just to be sure there's enough coolant for when it cools. Several cycles of this should be enough to expel all the air.

 

I would look at the fan clutch first, and put a shroud on it. that would be the best time, when the fans not in the way

 

Thanks guys. Tomorrow I will check the fan for movement. I did overfill the overflow tank and I have a couple of gallons on water behind the bench just in case. I will also start looking into a fan shroud. On that note, I have a manual tranny 4.9L without ac. According to LMC there are different shrouds for ac versus non ac. Does it really matter which one i get? I ask because I would like to find a good used one out of a wrecking yard if possible and save money.

 

A/C trucks usually have the "extra cooling" radiator and is wider than the non-a/c trucks, unless it was ordered with extra cooling with no a/c. There's two sets of threaded holes in the core support (drivers side), so if you are using the inside holes, it will be standard cooling, if you are using the outer set, it's the extra cooling radiator.

 

I checked the fan for movement by grabbing the top of one fan blade wiggling it forward and backward. It had quite a bit of play in it, so I presume it needs a new fan clutch. Is that correct?

 

Sure sound like it. Is the play coning from where the clutch shaft goes into the clutch? That's pretty typical on older clutches when they wear out.

 

Sorry to sound stupid, but I'm not sure. This is my first time with a fan clutch.

 

Assuming all the bolts and water pump are tight and you have play in the clutch, it's bad.

Doesn't sound stupid at all, that's why we're here.

 

The pulley is usually steel and painted black. The clutch is usually cast aluminum and is usually silver. That might help you determine what has play in it. If the black pulley is wiggling around, you have loose bolts or a worn out waterpump. If the black pulley sits still, and the silver part out front has the play in it, then that's the clutch and it's shot.

 

P.S. Get ready, you might have the fan clutch assembly that has very large threads, and it threads on the waterpump shaft with left hand threads. These can be fun to get off sometimes, and you also may need a special wrench(large) to get it off.

 

The nut is reverse thread. Keep all belts on until you have loosened it. A mechanic friend showed me a trick one time... With a long chisel and hammer, strike the edge of the flat of the nut and it will help loosen the nut.

Oops... I just reread Franklin2's post and saw that he mentioned left hand threads.