4age cooling system

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4age cooling system

Postby oldae82 » Fri Nov 03, 2017 4:41 am

Short history: I did a rebuild on my 4age in an '87 ae82. Installed a new water pump in the process. No overheating problems in break in period. At about 1000 miles, engines overheated drastically, and although I wasn't watching the gauge constantly, I think very quickly. Warped the head. Pulled the head, had it planed, reassembled it, installed a spare radiator, ran it through warm up and cool down cycles in the yard. Got heat from the heater, all hoses hot, cooling fan cycling. Ran the car up and down the road, all Ok, and then a sudden overheat, head gasket blown, white smoke etc. Pulled the cylinder head from the original engine with who knows how many miles on it, because now I've thrown way too much money into this thing. Reassembled it with a three layer steel head gasket, went through all the coolant bleeding procedures, as above, and have been running it some, maybe a 150 miles since the new gasket. I ran it a few days ago, about 10 miles, some of it to redline, no sign of overheating, got home and checked under the hood, because now I'm paranoid about it. Bottom radiator hose was cool, top hose hot, t-stat housing hot. Let it idle for 5-10 minutes, lower hose got hot, cooling fan cycled. Air temp about 50 F. This does not seem normal. It's been suggested that perhaps the impeller on the new water pump is loose on its shaft, and not impelling at higher rpm, but aside from that, a lot of head scratching.

What's the path of the coolant in the system? How does the bypass under the intake work? I read the thread about the bad temp sender connection, but my problem seems outside of that discussion. Any suggestions, short of pulling the water pump, which I'm not eager to do.

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Re: 4age cooling system

Postby Mehmaddict » Fri Nov 03, 2017 8:55 am

I had the same problem, My problem is air blocked in heater system. When you install the new water pump,
MAybe there is some air in your heater system, it will affect your water flowing.

I tried this.
Park somewhere a vehicle with the front upright. Turn heater to hot position. Dont start the car wait for the radiator cool, Then put some water with funnel. Start the car, Give some rev, and squeeze the hoses you will see bubbles. squeeze it when to water flows up and down. Put new water to radiator.

I dont know you know this or try this, But my 20V overheated quickly, and fans always working, WE try this, solved,

Good luck!
Never Gets Old //

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Re: 4age cooling system

Postby jondee86 » Sat Nov 04, 2017 1:49 am

I searched the interweb for a pic of the AE82 cooling system and couldn't find
one... so I made you one :) Don't know if it is 100% accurate for your car, but it
should be close enough for discussion purposes...


As you can see the thermostat is positioned so that when the engine is cold, the
return line from the radiator is blocked. In this situation water just circulates thru
the engine to promote faster warmup. But to make sure that the engine does not
overheat, the bypass pipe lets a small quantity of water flow from the head outlet
to the wax capsule side of the thermostat. Thus, when the engine reaches near
operating temperature, the thermostat will start to open and allow water to circulate
thru the radiator.

If you start a cold engine with the radiator cap off, to begin with there is no flow
in the top of the tank and the water remains cold. But when the thermostat begins
to open you will see flow in the top of the radiator and the top hose and header tank
will begine to warm up. This is normal.

When the car is being driven at normal traffic speeds, there is a lot of airflow thru
the radiator. While the top hose will get quite hot, the bottom hose can remain
quite cool and the electric fan will not be running. When you pull into your yard
and leave the car idling, the airflow thru the radiator becomes zero. The bottom
part of the radiator now gets hot, the lower hose gets hot, and the electric fan will
start to run. This is also normal.

So providing you have all the necessary pipes and hoses hooked up (if you don't have
a heater you need to install a loop of hose in place of the heater core) and the engine
is prone to sudden overheating, you need to start looking for anything that could
cause random blocking of the cooling system. One thing to check is the radiator hoses
to make sure that they don't get sucked flat when hot and floppy. Remember the g/f
you had in college, well that new water pump can suck pretty good too :-D Give the
engine a rev next time you come home from a drive and observe the hoses.

Cheers... jondee86
The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore, all progress
depends on the unreasonable man.

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Re: 4age cooling system

Postby oldae82 » Sat Nov 04, 2017 3:28 pm

Thank you both for the input. I put the car on an uphill slope and put a funnel in the radiator filler neck. I ran the engine to operating temp. I think I saw bubbles as it started circulating. I know by the time the fan had cycled a couple of times there were no bubbles.

Regarding circulation. If I understand correctly, when the engine is cold the water pump is pumping water through the block and also into the radiator. Because the t-stat is not open, the pump is pushing against the closed side of the t-stat, and no, or very little water is flowing through the radiator, and the bypass relieves the pressure. The main flow is through the block to the open side of the t-stat, and back through the block. When the t-stat does open flow through the radiator is permitted and flow through the bypass is diminished. I don't think I've got that quite right, but enough to see the path.

I did run it down the road after the uphill bleeding process, and checked the hoses afterwards. The bottom one was cool. It didn't collapse when I revved the engine, but that may not be definitive because it didn't have the full draw of the t-stat being open. I'll check it again when the lower hose is hot.

Again, my thanks to both of you.


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