truck is a 85 f150 with the 4.9. just put in an 89 motor made it carbed and got the clifford on. question is the truck is running to hot. the gauge is just below the H level as soon as it runs for about 5 to 8 mins. THought the sending unit was messed up. put a new sensor in. same problem. the water pump is new and i got the one for a 89. thermostat and housing are new but they are for a 85 since the head on it is made for an 85 pre emission. new hoses all the way around. coolant is new. My only question is could i have the heater hoses backwards. when i reassembled everything i didnt mark which hose went on which tube on the heater core. Does that really matter. I need to get this fixed. i may change out the t stat agian tomorrow and try that. Any info would be great. also nothing is leaking and there are no air pockets in the system. I have a funnel that bleeds the air

 

Have you tried a cooler thermostat? There are some that open at lower temperatures than others. I put a brand new 180 degree thermostat in my 4.9 and it overheated, so I switched to a thermostat that opens at 160 instead, that fixed the problem. they usually have the temp rating stamped on them.

 

The stock thermostat is a 195 I believe. Some even put in 210s to help with economy, so I don't think the thermostat is the first place to look. It looks like something else isn't doing it's job.

As for the heater core, it doesn't matter which goes where. It just a loop through the heater core and goes back into the system and really shouldn't have anything to do with engine cooling at all.

Is your radiator plugged? You never said anything about replacing that. You may just need a good, solid flush of the radiator to clean it out.

Also be completely sure there is no air in the cooling system.

If not, it's quite possible that your voltage regulator is simply bad. It's on the back of the dash and can make gauges read incorrectly. However, if this is bad, the other gauges should fluctuate accordingly. For example, your fuel gauge will read higher when your temp gauge is higher, and lower when your temp gauge is lower.

 

I would put a bucket under the rad. and drain it, then run the hose through it to see how it flows.

Also, is the big side of the thermostat facing the engine? I recently rebuilt an engine, and had the same problem. It turned out that the new thermostat was bad. It was also a 180 degree.

 

To add to what AbandonedBronco said... the voltage regulator being discussed is the Instrument Cluster Voltage Regulator [not the alternator voltage regulator]. If the ICVR is bad, all gauges except the ammeter will be affected.

 

before you tear anything apart, are you useing serp belt, or v belt. serp waterpump runs backwards, no good with v belt system, and vice versa.make sure to get the vapor lock out. take your cap of the radiator, top it off, start the truck and let it sit there idleing. turn on the heater to hot. air bubbles will start to come up where the cap goes, and will do this for quite a while. don't rush it. keep adding fluid as the level drops. eventually it will not bubble anymore, then top off the overflow, and put on your cap. if you see a lot of bubbles, and the antifreeze wants to spew out when you first start it, and you are sure that the waterpump is correct, you have a bad head gasket

 

Dusty about what you said with the water pump. the motor was for a 89 and had a serp belt system on it. i put the v belt on but used a water pump for an 89. so i got an 89 serp belt water pump on a v belt system, causing it to run backwards. So you think that is it then. i just have to get a water pump for an 85 with a v belt and i will be okay. How did you know it spins different

 

both look the same until you look at the impeller, you can see the difference then. I've done this twice. once on my 82 I6 [had a spare water pump] once on my 5.0 mustang[parts guy was an idiot] both times as soon as I started them. they imeditaly overheated, and blew out all thier water.