Another shot in the dark, but what about a bad radiator cap not allowing pressure to build?

 

What engine are we dealing with here? The 351m/400 takes a special t-stat versus the standard thermostat of Windsors, FE's and 429/460s

Josh

 

Should still get hot. The purpose of the pressure cap is to allow the system to get hotter than "normal" and not boil because fluid under pressure has a higher boiling point. Since yours isn't getting hot enough to boil the fluid as it is, that's not your problem.

 

X2 on what engine you are dealing with.

 

Sorry, 360 engine.

Check on the rad cap...

 

For one, you need a 192-195 t-stat.

#2, driving 15 minutes with 30 minutes of idling isn't very much, especially in sub 40 temps.

#3 you cannot rely on the factory gauge, it does a better job of telling the outside weather temp than it does engine temps.

#4 you mention the bottom hose "not getting warm" well it shouldn't really, it feeds the engine coolant that has been cooled from the radiator and fan. The upper hose should get fairly warm, too hot to touch, but the bottom you should be able to grab no matter what.

Josh

 

I have a 195 t-stat.

I think a 15min idle, then a 10 mile (15min) drive with multiple stops, and several spirited accelerations, then another 15min idle should be enough for the engine to reach operating temp. The needle barely moved. The heat from the heater core increases relative to the water temperature needle's position. I had a 7.3 powerstroke truck that would warm up to operating temp after the same routine.

I agree, the factory gauge probably isn't very accurate, but it is in fact working. I've ordered another water temp sender to make sure.

The upper hose does get warm, although I can hold on to it without hurting myself, so I still think the water temp isn't what it should be.

What does the bypass hose do? I'm reading looking at the water pump, and there's a "bypass hose" listed in the shop manual.

-MK

 

The factory gauge may not be terribly accurate but coupled with the fact that he can't get any hot air out of his heater it's a good clue that it really is running cold.

For what it's worth it was ~30 degrees today when I went to get pizza. The pizza place, according to Google is 4.2 miles away for a total of 12 minutes driving time. I got in the truck and started it. I let it warm up for less than 10 seconds before I started driving. By the time I got to the pizza place I did have heat. I shut the truck off while I went inside. I was inside for less than 5 minutes and came back out to start the truck back. While it had been sitting turned off the coolant in the top of the engine had continued to draw heat out of the heads but not circulate so the temp gauge was all the way up to around the M. Of course when I got some air moving over the radiator and coolant circulating it dropped significantly but I still managed to get decent heat out of the heater for the 4.2 miles back home.

Now unless my 302 just somehow puts out way more heat than his 360, it seems to me like him letting it warm up before driving, and then driving should have been plenty to get decent heat. Just my $0.02 though based on my own experiences.

 

Does this truck have A/C? There is a valve that controls the coolant into the heater core.

When re-installing the new core, was the foam surround in good condition?

Is this truck/ engine new to you? The head gasket(s) could have been installed backwards completely bypassing the block and heads.

Josh

 

The truck is new to me. The previous owner owned truck for 4 years, drove it minimally. Had the radiator, hoses, t-stat and housing replaced. Reported that the truck didn't have working heat. The intake and heads appear to never have been off this engine. It looks 40 years old with the appropriate amount of gunk around the intake and heads. Original manifolds too. If the heads have ever been off, it's been a matter of decades.

It was an original a/c truck, but all of the a/c equipment including condenser, compressor and lines have been removed. When this was done, they also removed the blend door to the left of the heater core. When I pulled the heater box off, I blocked off the outside air vent on the right of the heater box in order to get more heat from the heater core. The blower motor was inoperable when I bought the truck, but I wired it up through a relay and switch for now, and it works just fine and forces air through the vents.

The truck had the heater water valve. I left the vacuum lines hooked up, but replaced it with a ball valve so I knew water was getting to the heater core. The foam surround was in good shape when I reinstalled it to the new core.

-MK

 

It doesn't take long for gunk to build up.

Easy way to tell head gasket orientation is to look for the gasket "tab" at the FRONT of the block where the cylinder head meets the block. The tab should be visible on BOTH sides at the front and you should not see any tab at the REAR.

Josh

 

I might see the tabs, but I'm not really sure what they should look like. Can't see the back of the engine. I did some research about FE head gasket, and found a few people reporting overheating because of backwards head gaskets, but none not heating up. Also someone said that fel-pro gaskets don't have tabs.

Sure hope that isn't it...

 

Fel-Pros have the tabs.

Two things with backwards head gaskets...

1) The temp gauge will read low, but the BACK of the engine is running hot.

2) Hardly any coolant wll flow thru the heater hoses, therefore, no heat thru the core.

It's too dark and cold to take pictures tonight, and I have been trying to find pics on the Net of the FE head gasket orientation, but cannot find any.

Without the gunk you should see a good portion of the head gasket on the deck surface. The cylinder head is "relieved" at the corner so you can SEE the gasket tab.

Josh

 

I think I see what you're talking about, and I see both tabs at the corners.

 

Just wondering if Nathan's idea was ever tried, I think it will rules a few things out im sure. A good test for t-stats is put it in a pot of boiling water and measure when, or if it opens. Also, maybe dumb Q but make sure it is seated correctly and not upsidedown. Good luck!