Coolant circulation (1 Viewer)

[Not a Tumor]

I've got an overheating problem that has given me fits for the last two weeks.
I have an 86 FJ60 2f engine.
It overheats.
I have changed the thermostat after boiling it to make sure it works as it should. It's a 180F
I've replaced all hoses.
I've put in a new 4 core radiator and have checked with a garden hose and found no blockage.
It has a new heater core.
It does NOT blow smoke of any color.
I've done everything I can to make sure the system is free of air.
The water pump does NOT leak and the weep hole is clean and clear.
When it overheats, both heater core hoses get hot. The oil cooler hoses get hot. The top radiator hose gets hot.
Here's the part I can't figure out. The lower hose and lower parts of the radiator stay cold.
The lower hose will eventually get hot "ABOVE" the "T" where the heater core hose connects, but below that, the lower hose stays stone cold, even when my gauge reads 230 or above.
It's as if the radiator is blocked, but it isn't, I've checked.
I pulled the water pump off today and it looks really clean inside and the bearing is good.
I have checked with a garden hose to make sure that water circulates around the block and head, but that is sort of redundant because the head and block and oil cooler and heater core are the only parts of my system that do seem to circulate coolant.
I'm in the process of ordering a new water pump just because I've replaced everything else.
Any ideas??

 

[OSS]

When the engine is up to normal operating temp after driving it, everything is too hot to touch. So "hot" is normal.When the engine is started from cold and warms up, the thermostat eventually will crack open a little bit and hot coolant will begin to trickle into the upper radiator hose while the rest of it gets bypassed and recirculated back into the engine again (to keep it hot) .

When the thermostat just opens and begins to let hot coolant flow into the upper radiator hose, that upper hose will immediately begin to feel really hot and soon will be too hot to touch.

But the flow of coolant is still slow and the radiator is still filled with several gallons of stone cold coolant, so when you feel the lower radiator hose after starting (but not after driving hard for quite a while) the lower hose will feel cold because the coolant is flowing slowly through a cold radiator.

Same thing happens when the ambient air temperature is cool. If the air is cool, the new radiator can cool the coolant inside it so far down when at idle that the lower radiator hose will barely feel warm.

Since you've replaced every cooling component in the cruiser except the fan clutch- replace that just to take it out of the equation. They don't cost much. Water pumps only limit flow if they're clogged with jelled coolant gobs. Since yours is clean, it's not the problem.

I'd verify what the temperature really is with another temperature gauge or instrument to make sure the overheating "problem" isn't just a faulty gauge.

When the engine is up to normal operating temperature, the front of the radiator directly in front of the upper radiator hose should be a few degrees above the opening temperature of your thermostat when aiming a infrared temperature gun at it. 230° would be way too high and even 210°F should only be hit after driving the engine fast (up a hill).

As an anecdote, my 2F, which had been super reliable for 25 years began to run inexplicably hot. It wasn't until I removed the cylinder head that I discovered that many of the small cooling holes in the head gasket had gummed up with jellified coolant gum balls, blocking coolant flow to the head. After seeing that, it was obvious why the engine was running hot. After replacing the head gasket and radiator (for good luck) the engine temperature ran super steady at the correct temperature from then on.

 

[ff347]

I know a ton of variables apply to all these temperature questions, my advice is get one of these to really know what temperatures you are looking at.

Steiger Performance - Inline radiator hose temperature sensor adapter

www.steigerperformance.com

I was dealing with a temperature issue and chased all kinds of problems, it and a mechanical gauge will give you solid readings vs the stock gauge. I put a aluminum radiator, water pump, fan clutch, etc and amazed at how much the real temp can move on these engines.

 

[Not a Tumor]

I know a ton of variables apply to all these temperature questions, my advice is get one of these to really know what temperatures you are looking at.

Steiger Performance - Inline radiator hose temperature sensor adapter

www.steigerperformance.com

I was dealing with a temperature issue and chased all kinds of problems, it and a mechanical gauge will give you solid readings vs the stock gauge. I put a aluminum radiator, water pump, fan clutch, etc and amazed at how much the real temp can move on these engines.

That actually makes a lot of sense. It would definitely give me a more definitive picture of what's going on temp wise.

 

[Chad717]

I know a ton of variables apply to all these temperature questions, my advice is get one of these to really know what temperatures you are looking at.

Steiger Performance - Inline radiator hose temperature sensor adapter

www.steigerperformance.com

I was dealing with a temperature issue and chased all kinds of problems, it and a mechanical gauge will give you solid readings vs the stock gauge. I put a aluminum radiator, water pump, fan clutch, etc and amazed at how much the real temp can move on these engines.

You put this in the top radiator hose? I've got a mechanical gauge and I was just gonna put it in the spot on the back of the head as a stock replacement, but now I think it might be nice to have some redundancy.

 

[ff347]

Yes, it goes in the top hose. The stock gauge on my truck is "fairly" accurate, but this does offer a real view. (The second your thermostat opens for example)

 

[ff347]

In action.

 

[NeverGiveUpYota]

@ff347 would you mind adding a bit more info regarding the parts including wiring into the cab? I’m interested in doing this as well once I begin reassembly. Much appreciated!

 

[ff347]

@ff347 would you mind adding a bit more info regarding the parts including wiring into the cab? I’m interested in doing this as well once I begin reassembly. Much appreciated!

It has been years since I did this, I think everything you need comes from the link I posted. I got a mechanical gauge at Napa with an extra long probe wire, stab probe through firewall.

Mounted perfectly and done.
Two favorite gauges.

 

[OSS]

there's no good way to mount a mechanical temperature probe in the back of the engine. It's too big. The best spot for that large sensor is in the top radiator hose as shown. That way you can keep both sensors and gauges.

 

[NeverGiveUpYota]

It has been years since I did this, I think everything you need comes from the link I posted. I got a mechanical gauge at Napa with an extra long probe wire, stab probe through firewall. View attachment 2050812Mounted perfectly and done.
Two favorite gauges.

Thanks! That’s the same place I had a mechanical oil gauge on my first truck. I loved that one too. Such a sense of security.

 

[cruiserpilot]

I think OSS might be on to something. Straight engines seem to have a propensity for head gasket issues over time. I think because the rear 1-2 cylinders get hotter, depending on 4 or 6 cylinder I would consider a head gasket here. Seems excessive, but the kind of blockage he indicates is a good warning system to you. Personally, I would heed that.

 

[ff347]

@OSS

Do you think changing the radiator fluid more frequently would stop the "jellified coolant gumballs"?
What do you think the cause of those little treats would be?

 

[OSS]

Jellified coolant is usually caused by adding orange Dex-Cool coolant to the cooling system after a coolant drain & fill instead of the green gycol based coolant. Google "death cool".

If green glycol coolant has always been used with 100% certainty even by the previous owner of the vehicle and changed every 5 years or so, coolant sludge is not likely to form.

At some point in the past my cooling system did get filled with orange dex-cool coolant and it eventually wrecked my head gasket.

 

[Not a Tumor]

update. my coolant sensor was bad. I guess the whole thing through me because the top hose would be to hot to hold on to for very long, and the lower would be literally stone dead cold.
To be honest, the water pump, thermostat housing and bolts were all silicone'd in and all the hoses needed to be replaced anyway. So I'm going to look at it from the perspective that if I hadn't suspected a larger problem from the neglected appearance of the parts, those things could have failed me in the woods if not replaced. So in the long run, I've learned something and replaced things that needed to be replaced anyway. I'm still waiting for a new water pump gasket, and sensor and hoping that will be the end of it. Thank you for everybody's advice.

 

[hjdca]

Also, put in a Aisin FCT-049 fan clutch. This is the best one for our LCs. This will keep it cool by locking up the fan at the right time.

 

[Gretsch]

Also, put in a Aisin FCT-049 fan clutch. This is the best one for our LCs. This will keep it cool by locking up the fan at the right time.

X2 here. I replaced all my cooling parts and hoses even though they prolly did not need it. Seems the thing that keeps my truck the coolest is that fan clutch. I did not realize at the time how bad my old one was until I got the new one on there. It is nice to be able to hear it come on now and watch the temps drop as soon as it does. My belts are new enough still that they are stretching and I have to periodically re-tension them, the water pump belt especially. I can tell when it needs to be done from the temp gauge and the sound of the fan. Truck runs slightly warmer overall. Check the belt tension and sure enough it is loose. I tighten it up and temps go back to normal. Fan clutch for sure. HTH.