Coolant Reservoir Bubbles / Near Overheat

3

3rdGen2002

New member
Looking for some advice or experience on a potential overheat issue. Over the weekend I towed a small boat (~2500lbs) along with my family to the boat ramp. After getting the boat in the water and parking the truck I heard bubbling/ saw steam coming from under the hood. Popped it and saw my coolant reservoir tank was pressurized and bubbling. Popped the lid to the reservoir and lost about a quarter of the contents in that rookie move. The bubbling from the rad into the reservoir kept going for another minute or two and then stopped. The engine did not overheat (needle was higher than normal, but not in the danger zone).

I let the truck cool off and all has been well since then, including a drive home in 2wd and no A/C. My drive to and from work (~20 miles) went fine today. Radiator is still full. No coolant loss from the reservoir since then, fan comes on fine, temps are in range.

I'm hoping this is just a case where it was a hot summer day, I was towing a load, and had the A/C on which caused high temps but I've never had this happen before (that I know of). Perhaps I've just been spoiled by the reliability of the 4Runner before this and never encountered a simple overheat, but somewhere in the back of my mind I'm thinking there is a chance the head gasket could be the air-sucking culprit. New radiator, water pump and hoses 20,000 miles ago and thermostat 50,000 miles ago. 225,000 total.

Any input is very welcome! My novice search of the forum didn't come up with much.
 
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It's possible your overflow was just filled with water, and very hot coolant was going in making it bubble. Seen plenty of overflows with water only. The temp gauge doesn't start to move until about 225*, well past the boiling point of water.

It COULD also be that on the steep slope, you essentially burped your radiator of residual air that might have been in the system. Hard to say though.

New OEM radiator cap won't hurt though. It's part of a "Premium" maintenance package from Toyota.
 
I also vote for the clutch fan. Antifreeze at the proper concentration doesn't boil until at least 260 degrees.

Shutting off your engine caused heat soak.


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one way to reduce coolant temp is to turn on your front and rear heaters to dissipate some of the heat.

also, don't switch off the engine when overheating. park in a safe place, open the heaters, and keep the engine idling. if you can safely open the hood, do so.
 
Big shout out to hopeless diamond and Tim for the advice to check my radiator cap. Just took it off to inspect and found it broken. See pic attached. My only question is, what could have happened to the spring? Hope it's not rattling around in there...
 

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3rdGen2002 said:
Big shout out to hopeless diamond and Tim for the advice to check my radiator cap. Just took it off to inspect and found it broken. See pic attached. My only question is, what could have happened to the spring? Hope it's not rattling around in there...
Click to expand...

The spring and a plastic cap are inside your radiator. You could pull the radiator, turn it upside down and shake it around to get them out.
 
I guess they would have to be right... Sounds like I have a new weekend job coming up. Assume worst case is they bind up the water pump in the meantime?

Thanks again for the help!
 
Glad it was just the radiator cap but for future reference, once you see that needle move past the normal middle spot, you are already overheating. These engines do not handle being overheated well, it often ends bad.

You may want to consider monitoring your coolant temps more accurately with a scan gauge or ultra gauge. You can also set alarms and check codes with them (money well spent).

If you want something a little cheaper you can get a bluetooth obd2 reader and the torque app.

Good luck
 
I have made it a habit of buying a new radiator cap every time I replace a radiator for myself or someone else. They aren't very expensive but play a very important role.
 
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