1976 FJ40 2F Cooling System: Pressure Build With No Water Circulation?

[Ackcruisers]

I have seen a Thermostat installed upside down before ..............

installed by a TOYOTA Dealership here near DC ,

the truck was then towed to my Dealer ship where i was " Expected "

to wave a wand and know why in detail in under 420 seconds ...........


after a hour or 2 i pulled the top hose to verify the presence of a thermostat , and saw the bottom sticking up ?




a quick flip and a azzload of black FIPG later , she ran at proper operation

temp ...........

i also discovered , a 88c thermostat was installed by what ever knuckle head parts guy looked up the 90916-030 # # ...........

it should of had the lower temp one 82c

but the famed dealership service manager told me to :

" GET THAT THING OUT OF HERE NOW ! "


sad really ........

The OEM thermostat was replaced as my first step to mitigate the pressure observed. The images below are the old thermostat and housing. You’ll note, the thermostat really can fit in one direction as if flipped would bottom out in lower housing making the top not fit.

I ran the chemical test twice and the results came back as shown. If it turned yellow for gas engines, it would test positive for exhaust gasses entering cooling system. In both tests they came back blue. With the cap off, there was no pressure on the hoses. After twenty minutes+ the temp gauge inside truck shows 1/4 reading. This was with heat full blast.

 

[ToyotaMatt]

was that the exact thermost you just removed that was installed during the

symptoms ?

 

[Ackcruisers]

When the symptoms started, that thermostat was in the truck. I removed it along with the housing and replaced with OEM parts as shown. Plus new housing.

 

[Ackcruisers]

Here are some additional observations and questions:

1. With the chemical test performed, there were zero bubbles at the radiator fill neck. The engine, radiator and upper hose were all hot.
2. With the cap off, no pressure was observed with any of the hoses including top radiator, lower radiator and heater core.
3. The temp gauge maintained the reading of 1/4.

Questions:

A) If there were exhaust gasses in the cooling system, would there have been bubbles appearing at the radiator fill neck opening?

B) Is there a way to test the water pump for circulation? Or, would the engine over heat if circulation was inhibited?

This cooling system is very basic and wondering why the pressure and observed heat at radiator, hoses and thermostat housing is so significant while only at idle on a 70 degree day under zero load?

What am I missing?

 

[Cromagnon]

The only pressure regulating device is the radiator cap. A new one could be defective. I believe if there is an exhaust or compressed gas (from the cylinders) leak into the cooling system you would have detected it with the chemical detection system and seen some bubbles or gas coming out of the filler neck. With the pressure you are experiencing I would also believe that there would be some leakage of coolant into the lubricating oil or the exhaust system once you turn the engine off.

 

[Cromagnon]

It looks like loaner tools are available to accomplish testing of the cap and cooling system at Autozone, if there is one near you. If not, try your local parts house.

 

[Ackcruisers]

The only pressure regulating device is the radiator cap. A new one could be defective. I believe if there is an exhaust or compressed gas (from the cylinders) leak into the cooling system you would have detected it with the chemical detection system and seen some bubbles or gas coming out of the filler neck. With the pressure you are experiencing I would also believe that there would be some leakage of coolant into the lubricating oil or the exhaust system once you turn the engine off.

Good point. Yes. Last night prior to chemical test, after running engine for 10 minutes with a light load, I heard a slight sizzle sound (similar to a water droplet on frying pan). Only heard it a few times after engine shut down. It appeared it was coming from the carb on intake manifold. Again only a couple of times.

 

[Ackcruisers]

It looks like loaner tools are available to accomplish testing of the cap and cooling system at Autozone, if there is one near you. If not, try your local parts house.

Thanks for the suggestion. I’m getting radiator cooling system pressure tester now. The radiator cap was replaced with OEM 0.9 13 PSI cap when installing new thermostat and housing but new parts do fail.

 

[Solace in Solitude]

All your thermostat discussion reminded me that @SuperBuickGuy told me a few years ago that he always drills a small hole (1/8” IIRC) in the flange of his new thermostats, to prevent an “air-lock” or whatever he called it.

I’ve since read someone else’s post that said the same thing.

So, this trick would negate the need for burping a cooling system.

 

[Ackcruisers]

All your thermostat discussion reminded me that @SuperBuickGuy told me a few years ago that he always drills a small hole (1/8” IIRC) in the flange of his new thermostats, to prevent an “air-lock” or whatever he called it.

I’ve since read someone else’s post that said the same thing.

So, this trick would negate the need for burping a cooling system.

That‘s an interesting idea. The hole would permit the air to escape without thermostat open. If I need to dismantle mine, I’ll consider adding one. After pressure test yesterday, I discovered small leak in upper radiator hose. I‘m replacing hose today and will use spill free funnel to refill and burp. From there I will pressure test again and then use infrared temp gauge to see operating temp.

 

[Cromagnon]

If your radiator cap tests good I would believe the pressure that you are feeling on the radiator hoses is normal. The cap will release any excess coolant system pressure to atmosphere, through the overflow container.

 

[Ackcruisers]

Fixed radiator hose and ran another pressure test. Set pressure test at 13 PSI as shown and it held until I released the pressure (elapsed time of 40 minutes). No leaks anywhere.

I also filled radiator using Lisle Spill Free funnel. No bubbles observed after running for 30 minutes.

Using an infrared temp laser after 20 minutes, the following temps were observed:

Valve Cover: 143 - 153 degrees
Upper portion of radiator: 127 - 134 degrees, near cap 120 degrees
Thermostat top: 133 degrees
Water pump top portion: 147 degrees
Water pump lower portion: 127 degrees
Upper radiator hose: 147 degrees
Carb: 116 degrees

Heater core hose near outlet at top of engine: 166 degrees

Heater control hose before valve (128 degrees) after valve (108 degrees). Hose that goes to water pump (exit flow from heater core) - 130 degrees.

Intake Manifold: 277 degrees
Exhaust Manifold: 375 degrees
Exhaust flange: 377 degrees

Cylinder head near spark plug:
#1 - 158 degre
#2 - 162
#3 - 155
#4 - 158
#5 - 153
#6 - 144

Observations/Conclusions:

- The 13PSI pressure pumped into radiator for test was the same pressure felt on upper hose that lead me down this path. As @Cromagnon pointed out, this must be normal.

- Since the temp reading on Heater core hose before the heater control valve was 128 degrees then dropped to 108 degrees after the valve followed by reading of 130 degrees on the exit flow to pump, I believe the flow is restricted in some way in this loop.

 

[Cromagnon]

Very thorough diagnostics. The heater valve and core are going to be restrictive by nature and because of the thermal conductivity of the valve and the cooling effect of the heater core I would expect a temp drop. But not a 20 degree delta. If this was from the inlet of the heater to the outlet it would be plausible.

On the other hand I think you can conclude through empirical testing that your water pump is moving coolant and that your cooling system is healthy.

 

[Cromagnon]

Oh yea forgot one thing... THAT is a sweet engine bay!!!

 

[Ackcruisers]

Very thorough diagnostics. The heater valve and core are going to be restrictive by nature and because of the thermal conductivity of the valve and the cooling effect of the heater core I would expect a temp drop. But not a 20 degree delta. If this was from the inlet of the heater to the outlet it would be plausible.

On the other hand I think you can conclude through empirical testing that your water pump is moving coolant and that your cooling system is healthy.

Thanks for all your assistance/input, much appreciated. The diagnostic tool at AutoZone was high quality. Better than I would have been willing to pay as my cost per use would not justify investment. What a great service.

Yes, the data proves the coolant is moving through the system. I ended up removing the heater control valve hose again ( red arrow) to confirm flow. There was plenty of fluid flowing from top of engine block to HCV. What does not make sense is why the temp was higher once the fluid traveled through the heater core and then out to water pump. (Blue arrow). I’m going to get another temp reading tomorrow to try and duplicate the findings.

After 7 months of working on the truck I drove it today. Ran great and no overheating or pressure (outside normal range). My next task is to remove distributor, rotate it and put it back in.

 

[markyhemma]

The Vintage Air hoses are routed from the top of block next to temp sender and to lower radiator hose junction as shown.
View attachment 2306873
View attachment 2306874

That’s a really pretty engine compartment!