reece36

Hi all,

My 98 Tacoma 3.4L developed a small leak near the water pump (weep hole I suppose). It was just small enough to cause dried coolant build up on my starter cable but not enough to drip onto the floor. It's not due for a timing belt for another 20K miles. I thought I'd be smart and add Stop Leak until the tiiming belt and waterpump were replaced. Wrong move!!! Days after, the truck started to overheat in heavy stop and go traffic. It never overheated before. I flushed the system out several times, replaced the thermostat, then the fan clutch. The system is totally bleeded of air. I changed the oil, and there is no sign of water, so that rules out the head gasket. I'm pretty sure the water pump needs to be replaced because after the engine warms up, I can't feel a surge at the inlet hose after squeezing it for a few seconds. Currently, I can drive all day without overheating, but after sitting in heavy stop and go traffic for an extended period, it will overheat pretty quickly, nearing the red zone on the gauge. Curiously, if I turn the heater on full blast for less than 10 seconds, the temperature will rapidly return to normal, without having to turn the heater back on? What do you guys think? If my waterpump is shot, how can I drive all day without overheating? Any expanations for why turning the heater on for only a few seconds returns the temperature back to normal? Also, if the water pump is belt driven, what will cause it to fail?

Thanks in advance.
reece36

TACOMANATOR

If your water pump was toast you would be overheating all the time. Maybe a clogged radiator? The heater core is nothing but a small radiator so it makes sense that it cools down with the heater on.

MTL_4runner

Does the clutch on your fan work?
Did you remove the fan shroud for any reason?

Sounds like the whole system works fine at speed, but not when sitting still.
The fan is a mechanical setup but if the clutch wasn't working you would get enough airflow to cool the motor.

photoleif

i had a funky problem in another vehicle with a thermostat that was going bad on me. it actuated, but not reliably, and i could cool off the system sometimes by turning on the heat. new one worked fine, plus the heater worked better afterward too.

MTL_4runner

I agree, I'd replace the thermostat on this vehicle anyway just in case.

roger

I agree with Jamie. Check to see if your fan is turning on when you stop. At speed, you can get enough airflow over the rad to cool the engine, but when you stop it becomes a problem.

reece36

I replaced the fan clutch with an OEM unit and it is functioning properly. The thermostat that I replaced was from Kragen. Maybe I'll try an OEM unit and see how it works. Any ideas why turning on the heater momentarily returns the temperature back to normal almost instantly? Once the temp returns to normal, I don't have to use the heater anymore. It stabilizes.

reece36

Blair

Sounds like air in the system. When you bump the heat, the air bubble travels to the heater core, which explains why the condition doesn't return. When you park the truck, the vacuum draws the bubble back into the system. I'd try 'burping' the rad.

MTL_4runner

Just go and get an OEM thermostat and flush the cooling system and refill properly.
That should fix the either of the above conditions and hopefully stop the intermittent overheating for you.

bamachem

yup, you've got a bubble.

don't drain and refill, that will waste all that red-gold in there. just burp the system and if you have to drain, then catch it and reuse it...

MTL_4runner

I didn't know the price of coolant was that high now.
.....guess I better get out more.

bamachem

toyota red is expensive - for coolant anyway...

reece36

Just an update. I replaced the thermostat with a OEM unit and flushed out the radiator again. Overheating still persisted on steep grades and high traffic. Finally I purchased a radiator from toyautoparts.com for about $160. Truck has not overheated since. Problem solved.

So once again...

Added stop leak to cure waterpump leak.
Leak gone, but now overheating.
Flushed system.
Replaced thermostat and cap.
Replaced fan clutch.
Still overheating.
Replaced thermostat again.
Still overheating.
Replaced raditator.

Problem solved!!!