My 98 has been experiencing heating problems so I did the following.
Two new thermos, flushed several times, new water pump.
What I'm seeing now is my upper radiator hose is pumping up before the thermostat opens. Coolant is being forced out of the radiator cap until the engine warms up and than all seems to go back to normal once engine is fully warm. I do alot of short miles so I have to drive around for a while before all returns to normal. Engine oil is normal level and not changing. Truck runs great aside from this.
I'm thinking my headgasket leaking in to cooling system and pumping it up when it is cold but seals itself once it goes for a longer trip.
Does sound about right? Ideas/thoughts. TIA.

 

hmm doubtful... Do you see bubbles in the reservoir? sounds like a thermostat problem to me, but you said you have 2 new ones... hmm

 

Could be two bad theromstats.

Not to be a jerk just checking are you sure you are putting them in right side up?

Are you sure the serp belt is routed the proper way on the water pump?

Other than that it is prolly the head gasket though it is puzzling why it stops after she heats up??

 

You might have a partly blocked radiator. You should be able to run the truck with out a cap on the system. If coolant is flowing/spilling out of the cap a slow flowing rad would do this. as a check, If you blip the gas the coolant level should drop for a moment, if you get a "jet" of coolant thens its part blocked. Thermostats often get the blame but rarely fail, but you can test in hot water to make sure it opens.

 

I pulled a known working one from my 96 GT(same part number thermo) and bought another new one. Belt is routed correctly. I did see air bubbles once when I was filling up the degas tank but at the time thought it was air in the system. I guess trying to convince myself it is not something worse.....This has been going on for a few weeks now. It is puzzling why all returns to normal once warmed up.

 

uknig...That was a thought of mine as well. That was why I first did the flushes. Now just last week I pulled the radiator and bought some more zerex flush and soaked a full bottle of the stuff for hours in the radiator.After several rinses of water both hot and cold I was able to tell the full radiator was being used. First with cold. Then add hot water and feel the fins etc. Thanks for the advice but I'm pretty sure the radiator is flowing fine.

 

I am just taking a shot in the dark here. You said the upper rad hose swells up until hot. Have you watched the lower radiator hose to see if it is collapsing during this time? I have seen radiator hoses collapse when they get older and intermitenly stop coolant flow while the engine is running. Good luck

 

DYNO---my upper radiator hose is firm even before the thermo opens (cold)which is leading me to believe a headgasket faliure which is pumping into the cooling system. Or maybe even a cracked head some where on the exhaust side as I am not seeing any milky stuff on the dipstick. I guess I need to have my antifreeze analyzed for exhaust gases.

 

I think you may be right. The presence of hydrocarbons in the coolant would be a good/bad indicator. You should be able to see some hydrocarbons in the form of black spots, blotchs in the coolant reservoir. I am surprised though that you haven't mentioned any white sweet smelling smoke on initial startup thru the tail pipe. Depending on the severity of a head gasket leak it may not smoke very long so you have to have someone start it and you watch for smoke after the truck sat all night. The pressure in the cooling system will usually allow coolant to flow back into the suspect combustion chamber once the engine cools creating smoke on startup. I hope I am not leading you in the wrong direction but other than a partially blocked radiator which you already checked I can't think of anything else it could be. Someone already mentioned water pump direction and Tstat orientation. Good luck

 

What about a blocked heater core. Do you hear bubbling sounds from the passenger side even when you turn the engine off?

 

DYNO-I'll try sniffing the exhaust tomorrow before I leave for work in the morning. I have not noticed anything thou. My drive to work is about 2.5 miles so my exhaust isn't warmed up yet by the time I get there(still showing white out the pipe) and it has been pretty cold here lately. I just noticed this afternoon my lower rad hose was warm and upper was firm and cold. And coolant was seeping out the cap. This past weekend I took a longer trip (20 miles)while hauling wood on the way back and there was no white out the exhaust pipe.
tork-That may be a problem as well. But if it were clogged would that cause the symptoms i have?

 

I had a discussion today at work regarding your cooling problem. Every person I talked with said that your water pump is turning in the wrong direction. If you stand in front of your engine looking at it. The crank/damper is turning clockwise. The water pump should be turning counter clockwise. It is possible to route the belt the wrong way and have the water pump turn in the wrong direction. This may not be the problem but it would make sense that the flow would be reversed and you would be trying to push coolant past a closed t-stat. That would bulge your upper radiator hose until the T-stat opened. I know someone else here suggested the same thing but just in case check it out. Good luck

 

DYNO--How I wished you were right. But the pump is spinning counterclockwise..Just checked it out. However, I still have the old pump and when you spin it counterclockwise as if it were in the engine,the impellars 'L' is the part that is leading the direction of the turn. Just seems like it should be the other way but I am no fluild dynamics engineer.
Thanks for your advice..

 

Make SURE the part numbers match on your water pump. Been there before, just cause it bolts up doesn't mean anything! Double check your belt routing procedure with the sticker on the radiator cover. Not trying to make ya feels stupid, but crap happens. You never know what's going on. Before you take the truck to the shop, I would remove the t-stat completely and see if it still overheats.

 

chester-I compared the parts and looked at pictures from napa, cardone and advance and they all look like like the pump I replaced and the new one. I'm not having an overheating problem, the coolant is being pumped out the top of the cap if I keep it tight(building up pressure).. Then if I drive it long enough (20 miles) all seems to go back to normal(heat returns and coolant level in tank not to the top)..I will be driving around for a few days with the cap loose to keep it from pumping up and MAYBE get all the air out of the system. But air seems to be introduced in to the system everytime I start it up for the day... I have no problem changing the headgaskets myself I just don't wanna do it now, its tooo cold outside and my Mustang GT is taking up space in my garage where I would do my work. If I can get by till spring either the GT engine goes in the truck and a 4V(that I have not bought yet) engine goes in the GT. Or I just just do the PI head swap to the truck.Thanks to all for advice..
Gerald