Hello again,
Were talking about a '84 F350 Diesel that the air gets no hotter than luke warm. The upper and lower hoses seem to be moving water through the block so I think the themostat is working, the radiator is full of anti-freeze so thats not the problem. I am going to change the radiatior cap and see if that helps. Any other opinions would be welcomed.
Thanks,
Steve
Doc3544(No Email Addresses In Posts!)

 

There is a valve located usually on one of the heater hoses. Make sure the valve is funtioning properly. There will ba a cable attached to a lever or arm on the valve. Have someone operate the cold to hot control inside your truck cab while you watch to see if the arm is moving. Other that that, I'm lost unless your thermostat isn't working properly.

 

Your heater core could be blocked and/or the fins could be corroded off reducing the surface area to heat the incoming air. If you see the valve (mentioned in the previous post) moving and the hose gets hot, you have a bad heater core.

 

Does the engine temp register warm on the temp gauge?
Take the thermostat out and make sure it is closing all the way. If it is, put it in a pan of water and bring the water to a boil with a candy thermometer in it so you can see at what temp it opens. It is probably either not closing all the way, is opening too soon or is the wrong thermostat (180 instead of 195 or whatever it takes). If it is indeed functioning properly then there is something wrong with your heater core.

 

My '91 IDI has the same problem. The heater gets barely warm enough to warm up the interior after maybe 20 minutes on the freeway. I've gone through the entire cooling system, thermostat, heater controls, etc. I know of two other early 90's IDIs with the same problem. I have resisted the temptation to install a higher temp thermostat so I don't compromise my summer cooling. I read somewhere that some Ford diesels are chronically cold-blooded and I should just live with it, which I'm not quite ready to accept; I hope somebody has a better idea....

 

Diesel engines have a large capacity cooling system which necessitates a high temp thermostat to get the heater going (don't worry about over heating -- it ain't going to happen unless you've got something else wrong. This is why they use the exhaust back pressure device on the Power Strokes -- its solitary purpose is to get the heater going as fast as possible.
I used to run these 6.9 and 7.3 IDI engines on our dyno so hard that the exhaust manifolds and pipes would turn red all the way to the floor. When I was done running it, I'd leave it idle and as it sat there idling, I could watch the water outlet temprature readout and see the thermostat close.

 

So you think a hotter themostat will be ok in the summer? I hate to be changing them every season....its not so bad in a gas engine but with this truck is going to be a pain in the butt just to get to the damn thing. Oh well I am in process of swaping motors in another project this weekend I will change the thermostat somtime this next week and let you know how it turns out.
Thanks for the advice,
Steve :7

 

Yes, the only time I would change thermostats is when it goes bad. I don't remember whether we used a 195 or a 197 on that engine. Have NAPA or Ford look it up for you.
In fact, I don't see any reason to change them in your gassers, especially if they are fuel injected. Use what the manufacturer recommends. Get 'em hot and keep 'em that way, they'll run more effeciently if they are run within the parameters of the design.
The idea of changing to a cooler thermostat for summer use was born in the days when alcohol was used for antifreeze. Water boils at 212 degrees at sea level. A 50/50 ethelyne glychol antifreeze mix raises that to 220 and the pressure in the system raises it 3 degrees for every pound of pressure you've got, so if you're using a 17 lb. radiator cap your coolant won't boil until it reaches 271 degrees (at sea level).

 

 

Twin peaks.........could be a broken, jammed blend door too in the heater plenum.

CAUTION:
The specified/required thermostat does not contain an internal bypass, since the bypass is located in the cylinder block. Whenever the thermostat is replaced, it is mandatory that only Motorcraft E5TZ-8575-C or Navistar 1807974C94 thermostat be installed.

CAUTION:
Do not attempt to repair any thermostat. It should be replaced if it is not operating properly.

Check the new thermostat before installing it for correct opening temperature. Before suspending in boiling water, with a flashlight check where the rubber and the flat metal flange meet for bad seal. Tstat should start to opening barely at 180-192f, fully open 200-212f, allow to cool and check for rubber seal again.

Removal: Disconnect batteries, drain 4+ gals A/F, remove: as required, fan belt, alternator set aside, alt bracket, remove filter support from fuel filter then e/block. Disconnect upper rad hose at rad, remove tstat bolts and housing. Clean both faces, depression and holes in block, ensure check ball in goosekneck is clean, free and rattles "do not remove".
Installation is reverse proceedure, I do not use sealant on gaskets and faces. REMEMBER the tstat pellet(copper end) goes into the block. I do use a "very small amount" of sealant on the edge of the tstat face when installing into the recess, now go for coffee, allow sealant to setup, this has saved me from tstat slippage when the gasket and goosekneck are installed. Replace all items in reverse order......

Manifold bolt torque......... 20ftlbs


Legendary.......

Oil in the antifreeze is usually oil cooler orings leaking, however coolant in the oil could be one of several things, worst....cavitation, best water pump was changed and no sealant was installed on the 2 upper and 2 lower bolt threads and heads as is required. Make your own post if you want to continue this.......ok