1990 F150, 5.0L V-8: Temp guage indicating well past normal. Got home ok as the temp didn't get fully over to HOT and the engine sounded ok with no steam or leaks noticed. The temp guage actually went down close to normal if at highway speed but immediately went back up after slowing down or stopping. After letting the engine cool down, noticed the overflow tank was nearly full but the radiator was about half full or slightly less. No leaks in the system were evident. All hoses have been replaced within the last five years or so. Removed the thermostat and checked it in a pan of hot water and it seemed to open when the water started to boil. Let the pan cool down a bit and heated back up to boiling and the thermostat again seemed to open ok. I plan to replace the thermostat just because and see what happens. Wondering what else could be a cause for this to happen? Thanks!

 

does your truck have a fan clutch and if so is there any evidence of leaking silicone fluid from it? If so that's possibly your problem. I don't like that the thermostat doesn't open until boiling, either, it shoudl open about 195F not 212F. I just had this exact same experience yesterday with my 300 straight six, replaced the fan clutch this AM. Had to buy a special wrench and a pulley holder as well as the fan clutch is threaded onto the water pump shaft not held on with four bolts as is standard.

Also check the overflow hose from the rad filler neck to the coolant recovery bottle; mine was originally just pushed on at the filler neck and held on with an Oetiker clamp at the bottle; the clamp was rusted away so it was leaking at both ends. what that meant was that the coolant would overflow but when the system cooled and tried to suck it back in it'd suck air. Had to get some little stainless mini clamps to get it all working right again. (the hoses were also swapped at the filler neck when I bought the truck, but I don't know if that was from the factory or a previous mechanic not paying attention. I think I posted about that here when I first bought the truck. Other than replacing the fan clutch this AM everything's been all good since I fixed those initial problems.)

good luck

nate

 

Hey Nate,
Thanks! I did replace the thermostat today and when I went to fill the radiator I noticed a steady drip coming from a hole in the bottom of the water pump housing??? I thought "that's not a good sign" but decided to give it a try anyway. So I fired 'er up and left the cap off until the engine reached operating temp. Had to add some more fluid a few times until it seemed full. Total, I added about close to a gallon of fluid. Put the cap back on tight. The leak seemed to quit and took it for a short ride. The temp needle stayed down low in the normal range. So far no leaks. Kind of a mystery yet? This truck does have a fan clutch but seems to be working ok. Still don't know what the leak in the fan housing was all about yet?? Any thoughts? Thanks!
PGDH

 

that leak from the weep hole is your warning that your water pump seals have failed, go ahead and replace the water pump before the bearings go. Whether or not to replace the fan clutch is up to you, but you'll have to remove it to replace the water pump obviously so you'll still need the tools if you DIY. You may be able to rent them from your FLAPS if you're really on a budget. Or if you're near me and it has a 40mm nut I just bought them this AM

good luck

nate

 

its been a while since I did mine, but theres a little slot at the bottom of the waterpump, the weep hole, which will start to leak once the pump is going out. If the leak is comming from there, it wouldnt be a bad idea to spend $30 on a new pump and replace it. It will only take half a day. Start soaking the bolts down because they are known to break I guess. Also, when you go to the store, pick up blue RTV and threadlocker.

 

Hey thanks for the info guys! It's not really what I wanted to hear but it's something I sort of expected about the water pump. I try to be a DIY'er so will give it a try. At least this is happening before the weather turns nasty; which could be really nasty in the Great North Woods of MN!

pgdh

 

I hear you on that, although the snow makes it pretty easy to see if its oil or coolant. last winter I had a leak between the timing chain cover and block where the coolant inlet is. Good thing I had a heated garage to go into!

Doing the waterpump isnt that difficult or stressfull. You'll have to take off the power steering and a/c(as in, just throwing it aside, not disconnecting the hoses) clutch fan and fan shroud. Otherwise its basically taking bolts out and putting them back in. unlike doing the heads where you have to worry about coolant getting into the oil!.

Try cleaning off the bolts. I used a wire brush on a dremel(or drill) to clean the sludge off the threads for a more accurate tourqe reading, and for the thread sealer to hold. Also, clean the gasket surface on the block(really the timing chain cover) with the wire wheel or scotchbrite pad.

With the old gasket or peice of cardboard, keep the bolts in the same place for installation.

Coat the gasket with RTV on both sides. Doesnt have to be a big bead, just enough to seal it.

 

Hey thanks again! You've given me some confidence about doing the job. Your tips on doing it are greatly appreciated! I plan to check around tomorrow to get a price on a new water pump and I suppose I might as well do the fan clutch as well..... I'll have to check if the new gasket comes with the pump or separate. I'll let you know how it turns out! I'm hoping to keep this old truck running as long as I can, it's been pretty good to me over the years........
pgdh

 

If it makes you feel any better, I drove my truck to work today because I was too lazy to transfer all the crap in it into my car, and it read between "N" and "O" of "NORMAL" at all times (still hot, still stop and go traffic,) new fan clutch fixed it right up. I'd still go ahead and replace your water pump in your case. I don't know how hard it is on a 5.0 but on the old 300 the fan clutch was a piece of cake (once I got the right tools) and the water pump, if I'd needed it, I probably could have done in another hour at most working slow. Only regret I had was not having a bead blaster handy to derust/repaint the fan blades (yeah, I'm weird like that. I like everything I work on to look shiny and new) Pick up some new hose clamps too, you never know if you're going to have to cut one of the old ones off. Generally a new/reman water pump should come with all the gaskets you need to replace it, but it doesn't hurt to check before you leave the store.

good luck

nate

 

Update: Picked up a new pump and gasket today, thirty six bucks. Got home and got started about 12:30 pm or so. Had a few distractions during the pm so didn't get finished. Everything came off pretty good except for the old pump gasket.... It was stuck on really good! Took about an hour to get it all scraped off. Used some "goo gone" and it seemed to help some but still had to scrape and scrub to get down to bare metal. Shouldn't take too long to finish up tomorrow, I hope... The fan clutch is still tight and smooth working and still seems to be ok so will take a chance on that and just ckeck it more often. Will give another update tomorrow night... Thanks again! It's great to have a place like this to go to and get such great support!

pgdh

 

I know you already bought the pump, but let me give some advice anyway. Buy a motorcraft pump. The cheap aftermarket pumps from Autozone will last a year or two before they go out. Sure, you get a lifetime warranty, but what for? So you can spend four hours every other year replacing a part that lasted 20 originally?

 

I was wondering why the CarQuest pump was so cheap?? They didn't even tell me about any warranty?? At least I know I can do the job now so if it goes two years I'll consider the Motorcraft one. Thanks! Anyway, I finished up today and it went back together well, filled'er back up and let it warm up good with the heater on hot with the fan on high and the cap loose. The level dropped a bit and added enough to top it off. Took about 9 or 10 qts. I suppose I should have done a system flush with the old pump but I didn't think of it in time..... CRS!?## I took it for a short spin and the temp guage barely made it past "no" I was happy! Wonder what's going to go bad next?? About a month ago I had to replace the ignition module. First time I ever got stranded on the highway with this truck. Had to call for a tow. Luckily I had towing coverage with my insurance company.

Thanks again for all the tips and suggestions!

pgdh

 

In general Carquest seems to be a decent parts chain, up there with NAPA and definitely higher on the food chain than Pep Boys, AutoZone, et. al. - just my experiences. Don't lose any sleep over it.

nate