Ok, working on a '99 with 3.0 and 5spd. Belongs to young brother in law that takes care of nothing .

Its been running hot. Before it came to me, the thermostat was replaced and a alot of bars leak added due to a pin hole in the filler tube of the rad. I pulled the radiator, weighed a ton and looked like it was full of red Georgia clay. I went ahead and replaced the radiator, water pump and upper hose. The lower hose is fairly new and passed a good visual inspection. I flushed the heater hoses and the block as best as possible. Got it back together and filled with 50/50. Cranked and ran to operating temp. Cold air only from heater. Bled air from thermo housing. Ran (didn't drive) again, ran great with plenty of heat from the heater. Took for a DRIVE last night. Made it about 2 miles. The gauge SPIKES, and I get cold air only from the heater. Then suddenly gauge drops to normal and heat comes on. Then it repeats over and over. Im thinking air pocket again or maybe the thermostat was put in backwards!?!?! Maybe a blown Head gasket?!?!!? No smoke or other signs of trouble. Im looking for other ideas to check? Please give me your thoughts.....

 

A few thoughts. I would try and see if it is an air bubble. I think if you park on as steep of a hill as possible and let it run. That can help get out an air bubble. It has something to do with the rad being higher than the tstat or something like that. I doubt it is the HG with what you said. Any coolant loss, milky substance on oil cap, exhaust? I don't know about the 3.0 but on my truck it would be tough to install the tstat backwards

 

Thanks for the response. No coolant loss other than that backflow that overflowed the reservoir. I've bled the air twice. Didn't seem to have any air the second time. I'll try the incline..... Oil is good. Oil cap looks good...... Not sure about the tstat, how it fits, up or down, etc..... It was changed just before I started working on it. I know the upeer hose gets real firm. To me it seems the tstat is bad or failing but Im open for more suggestions.

 

You prob should just replace the tstat since there is nothing else left. Imho I would only use a Motorcraft tstat. I went thru 2 others brands on my truck before I used a motorcraft and it solved the issue

 

Use any stock thermstat, but when you install it, you have to install it with the little "air burper" button on the top and the spring side towards the engine. The motorcraft brands are made in Germany and have a better "air burper"
The burper button is on the flat round disk.

 

the mororcraft has the built in burper and i guess you can jury-rig something different. I have used non motorcraft tstat and the gaskets where different and thuse allowed blowby. I only use motorcraft tstat now. You will have to decide what to use

 

i just had a tstat replaced and the indy used a stant ... the new kind. it's working, for now...

 

Thanks for the replys. Not to worry, I use only quality parts, motorcraft or otherwise.

OK so it looks like everyone agrees that the tstat is the likely culprit here. I guess im trying to give benefit of doubt to the installer that it was done correctly. He's a fine (shade tree) mechanic but was assisted by the young owner who has no pride in his ride. I haven't had a chance to check/replace the tstat. I'll give an update when I can. Meanwhile, if there are other suggestions please post them up ...

 

Just before winter started I was loosing coolant through my exhaust. I have been having a head gasket leak with light peanut butter colored gunk on my oil cap without any water noticed when I did complete oil changes. My radiator had to be replaced after trying 3 different cooling system "fixes"......Bards,K&W Block seal, and another metal containing solution.....none of which cured my coolant loss. I finally used a product called "Blue Devil", and it worked for a year and 3 months. At that time it cost $ 90.00/qt and I had to use 1/2 qt for my cooling capacity. If you have done any cooling system flush you know you have to remove your thermostst during the cleaning process.
Now to the moral of this post....I went to get a Slant brand thermostst....The cheapest one had the burper, but the Slant Super, which cost alot more, didn't have a burper at all. I asked the parts guy what the difference was and he didn't know. So I bought the Super. That night I dug through my old parts box and found one of my old Mototcraft. I tasted both in a pan of hot water and a thermometer on the stove. They both opened and closed, but the ole Motorcraft have a burper and the Slant Super didn't.
I installed the Slant Super and had the problems you described in you original post with an erratic movements of the temp gauge. I tried "PawPaw's" park on the incline trick.....ran the truck up to normal operating temp 3 times, and it didn't work. I finally put my Motorcraft thermostat w/burper in with the burper in the upper position. I haven't had a problem since.
Please note that I change my engine oil every 3,000 miles..castrol 10w40 and Mobil 1 filter mainly to keep an eye on my oil status and because the age of my engine.

 

+1 on mramels comment I was thinking the same thing about removing the tstat for the flush. To the OPer the only thing that you might have not done perfect is removing the tstat especially with the red clay comment

 

Ahhhh, Gotcha.... The tstat had been replaced just days before I started working on the truck. It had been cranked once with the new tstat so I thought "no way" that could be an issue. I never considered that the stop leak buildup could've been a factor for the tstat failure. Ok, I'll replace the tstat and check inside the housing for any buildup. I'll flush it again if necessary. I'll post back with success or failure update. Thanks agin for the assist.

 

What I think you've got (and please don't shoot the messenger) is a whole bunch of pieces of stop leak all through that block and heads now. Member that red georgia clay lookin stuff?

I have seen it form a solid brick in a radiator before, and if it can do it in there it may have done the same all up and through that motor.

That there is why I never add mud to my radiator - if there is a leak, I fix the leak. A shortcut in a can is sometimes the longest and most expensive way around

 

Oh trust me .... I agree 100%. I never use the stuff either. Its not my truck. I have a 97 Exped, 07 Exped an 09 Crown Vic. This is my bro-in-laws and he isnt very mechanical at all, lol. His step dad is the more mechanical person but he lives 4 hrs NE. So I offered to work on it and found a mud slide inside. From what I understand the rediator was flushed last summer and the stop leak was added around Christmas. So im hopeful that it isnt too clogged to flush properly. Im going to start over and drain everthing, flush it again, replace the tstat, and see what happens.

 

UPDATE:

Ok, I pulled the new tstat, flushed everthing again, installed another new tstat, replaced the 50/50, and took a ride. It obviously still had an air pocket because it was blowing nothing but cold air. I did a "quick stop" and I guess it shifted to coolant enough to open the tstat. Went on a 15 minute ride changing the HVAC from heat to max air and back seceral times with no issues. The temp gauge still flexs alot between "C" and half way to "H" (norm run temp). I guess all that stop leak gunked up the other tstat. Anyway, its back on the road. Thanks for the assist.

 

Glad you got it working. One thought if the gauge is flutating when you rev the engine. You might be low on coolant.