1976 FJ40 2F Cooling System: Pressure Build With No Water Circulation? (1 Viewer)

[Ackcruisers]

Started truck and drove 4 miles for a total of about 20 minutes. Noticed top radiator hose had a lot of pressure and the newly replaced radiator cap was functioning to allow the overflow into reservoir. The radiator was very hot as well as the new thermostat and housing. I let engine cool for few hours in garage. Pressure on top hose was gone and expansion tank was now near empty (functioning as it should).

The lower radiator hose feels like there is no coolant in it when squeezed, nor is there any fluid in the heater hoses that flow into my Vintage Air system.

Unfortunately, I believe the cooling system is blocked somewhere. The radiator is new as well as the water pump, thermostat and housing (top and bottom).

The engine was rebuilt and has less than 50 miles on it but it sat for past 7 months. Could there be rust, gunk and scaling in the engine causing blockage? If so, what is the best approach to remedy?

 

[Dizzy]

You can always drain the coolant, from the block and the radiator, into a clean container for inspection. The heater line loop might be restricted, you could check into that while the coolant is drained. I'd look for RTV or rust in the heater loop.

The system is supposed to be pressurized, as maintained by the radiator cap. Is your radiator new?

 

[Solace in Solitude]

Have you tried burping the cooling system?

An air blockage is as bad as a gunk blockage... and is more likely, on a recently refilled cooling system.

Search... there are many threads... here’s one... read up on burping —>Coolant bubble / burping question

 

[Ackcruisers]

You can always drain the coolant, from the block and the radiator, into a clean container for inspection. The heater line loop might be restricted, you could check into that while the coolant is drained. I'd look for RTV or rust in the heater loop.

The system is supposed to be pressurized, as maintained by the radiator cap. Is your radiator new?

Thanks. The radiator is a new 4 row type. I hope there is no RTV in the system but you never know. For my thermostat and housing install, I used a very small amount of gasket sealer. My heater line loop is for the vintage air unit. There is a hose that comes out the intake next to temp sensor and runs to a heater control valve and into the heater core. From there it goes out to T fitting below water pump.

 

[Ackcruisers]

Have you tried burping the cooling system?

An air blockage is as bad as a gunk blockage... and is more likely, on a recently refilled cooling system.

Search... there are many threads... here’s one... read up on burping —>Coolant bubble / burping question

Many thanks. Given that the engine was rebuilt with 50 miles, new water pump, heater, hoses, radiator, thermostat and housing - it is likely air is trapped causing my issue. I’m going to follow FSM to drain system to confirm and verify condition of coolant. While at it, will flush with distilled H20. Also, will remove heater loop from intake and flush heater core to verify condition.

There are a lot of opinions on the best approach to take for burping a 2F engine... I will continue to search to find the best approach/process and will post links here if found.

 

[Dizzy]

I ran one of those Gano (brand) filters on my heater line, and one on the upper radiator hose. The heater line trapped quite a bit of sediment, almost to the point of blockage, and I removed it because the fitting loosened up and I didn't want to risk it. The (clear) upper hose filter gave me an indication of coolant moving from the thermostat to the radiator, as I could see micro bubbles and smaller than the screen particles move, even more with the engine revved. It was virtually free of sediment, a bit prone to leak, and I removed it thinking that I didn't want the vulnerability of it leaking.

If the sender unit is telling you that you aren't overheating, then, you are probably okay.

On my other vehicle, an entire region of the block's water jacket had an obstruction. I pulled the drain plug, and there was nothing, not even wetness. I poked a wire into the cavity for a few minutes and finally got water to come out. I'm a big fan of annual coolant (and hydraulic fluid) changes on my vehicles. If nothing else, just for inspection.

 

[pb4ugo]

A hot radiator is an indication that water has been circulating. Was the upper rad hose hot when you squeezed it? The upper hose should get hot when the tstat opens.

 

[Ackcruisers]

A hot radiator is an indication that water has been circulating. Was the upper rad hose hot when you squeezed it? The upper hose should get hot when the tstat opens.

The upper radiator hose is hot and very pressurized. Just tested engine again after confirming no obstruction in heater core and lines going in and out. Fluid appears normal and pink (Toyota OEM 50/50 fluid). Is it normal for the upper radiator hose to have pressure vs. lower hose as the water pump is pumping flow up to radiator? Temp gauge is showing middle.

 

[73FJ40]

The pump is also sucking water from the radiator.

 

[pb4ugo]

When cold And the engine is running, You can put your hand on the upper hose. When you start to feel heat quickly in the hose, the t stat has opened. Then the rad get hot. While the water gets to operating temp, the cooling system builds pressure. Water will boil at a higher temp when under pressure. The rad cap is designed to hold pressure up to a certain point. Then the water gets cooled by going thru the rad and leaves going thru the lower hose, plus the pump is pulling it out of the rad. Basically, When the engine is cold coolant is recirculated in the engine till it get warm enuff to open the t stat and then water starts to flow thru the rad.

 

[Ackcruisers]

The only way that I'll be confident the system is functioning as it should is to do a full coolant flush and refill.

 

[numby]

This is also a near matching symptom of a blown head gasket. The system will pressurize as exhaust gasses are forced into the water jackets in the cylinder head and then straight to the top hose of the radiator. I just had this issue on a non-toyota straight six engine.

Six months (or a year) of sitting around with all that fresh coolant would not create a problem with scale/rust/slag/electrolysis/etc.

Your engine is new so this probably isn't your issue but I felt it best to mention. Pull the thermostat and check for correct opening temp just to be safe. You could also try running it for a few minutes without the t-stat to see if it exhibits the same behavior.

 

[Ackcruisers]

This is also a near matching symptom of a blown head gasket. The system will pressurize as exhaust gasses are forced into the water jackets in the cylinder head and then straight to the top hose of the radiator. I just had this issue on a non-toyota straight six engine.

Six months (or a year) of sitting around with all that fresh coolant would not create a problem with scale/rust/slag/electrolysis/etc.

Your engine is new so this probably isn't your issue but I felt it best to mention. Pull the thermostat and check for correct opening temp just to be safe. You could also try running it for a few minutes without the t-stat to see if it exhibits the same behavior.

Thanks for posting. It’s very very unlikely the head gasket is blown. Below are images of the newly installed gasket 50 miles ago plus image of motor assembled.

 

[Solace in Solitude]

I burp mine by climbing up (forward) a 30*+ incline, chock the rear tires, leave it in neutral with parking brake on, turn heater on, open hood, remove radiator cap and run it until bubbles quit coming out of the radiator fill...

Heater On will include the heater in the burp.

If you’re flushing the coolant, be sure to drain the block... small petcock halfway up block on drivers side, Between cylinder5 & 6... flushing will obviously necessitate another burp.

 

[Ackcruisers]

I burp mine by climbing up (forward) a 30*+ incline, chock the rear tires, leave it in neutral with parking brake on, turn heater on, open hood, remove radiator cap and run it until bubbles quit coming out of the radiator fill...

Heater On will include the heater in the burp.

If you’re flushing the coolant, be sure to drain the block... small petcock halfway up block on drivers side, Between cylinder5 & 6... flushing will obviously necessitate another burp.

Thanks for sharing your method. I started the process of draining coolant from the block via the block drain plug and as soon as I backed off the bolt, I captured enough fluid in clear plastic cup to closely inspect fluid quality without draining. The Toyota 50/50 antifreeze was clean and looked the same color as if it were new.

I decided to just jack up the front end and run the engine following your process. The top radiator hose was pressurized but so now was the lower radiator hose as well as the Vintage Air heater core hoses. Ran engine with cap off then fluid began to flow over top of radiator fill so put cap back on and the fluid was pushed into overflow reservoir. The temperature gauge now stayed between cold and half way. This is how my 1969 FJ40 temp gauge read many years ago.

I think the issue must have been air pocket related vs a clog in system. While the jury is still out, I’m leaning more towards air in system caused by removing the Vintage Air system and hoses. Air was introduced since I simply reconnected the two heater core hoses and then topped off radiator without burping.

 

[Dizzy]

I heard that if you take the radiator cap off and idle it, the exhaust of a blown head gasket will bubble up the radiator and you can visually see it as the engine runs, especially at rpm. No experience here, though. At 600 miles after the rebuild, the cylinder head bolts need to be checked for torque, according to repair / maintenance manual.

How are the Vintage Air System heater hoses routed? On the OEM heater core, there is a top hose to the the head, and a lower hose to the lower radiator hose, IIRC.

 

[Ackcruisers]

Thanks @Dizzy and everyone who has weighed in. I’m going to attempt to burp the system one more time. Next I’m going to buy a chemical tester to see if there are exhaust gasses inside the cooling system. There is just too much pressure on all the hoses for this to be normal. My next step is leakdown test. @numby suggestion to explore possibility of head gasket blown (or cracked block, warped cylinder etc) is an unfortunate possibility as I did not restore the motor myself.

 

[Ackcruisers]

I heard that if you take the radiator cap off and idle it, the exhaust of a blown head gasket will bubble up the radiator and you can visually see it as the engine runs, especially at rpm. No experience here, though. At 600 miles after the rebuild, the cylinder head bolts need to be checked for torque, according to repair / maintenance manual.

How are the Vintage Air System heater hoses routed? On the OEM heater core, there is a top hose to the the head, and a lower hose to the lower radiator hose, IIRC.

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

 

[ToyotaMatt]

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 ........

 

[WildernessRimFab]

A radiator funnel would be a good thing to try. Once you see them in action you will never go without.
Filling up the funnel adds additional pressure to the system which helps to burp it.
Also, coolant expands when hot so you can run the truck up to temp and let it cool back down with the funnel full.
There is a plug so you can remove the full funnel without spilling.
Lisle 24610 Spill-Free Funnel
Amazon product ASIN B00A6AS6LY