Guys,

I have been having an issue with my 2002 4Runner with about 64,000 miles overheating. This first happened over a year ago and at that time I suspected the thermostat and replaced it and the fluid. That seemed to do the trick for about a year until it happened again about 4 months ago. I went ahead and replaced the thermostat again, but now I am back where I started. I am not sure if the issue is the water pump (I don't hear it making any noise) or maybe the clutch fan? I was thinking of just going ahead and covering all my bases and replacing the clutch fan, water pump, hoses, and t-stat this weekend. I am curious to know what you guys think and also IF I replace the waterpump will I have to remove the timing belt? Thanks for the help!!

Do you do a lot of off-roading and especially any mudding? If so an additional thing to do would be to run a lot of water through the fins of the radiator. I have seen some that look pretty clean but after running a hose to them for a good bit all sorts of dirt and stuff got cleaned out of the fins.

As far as the other issues I am sorry to hear about your problems. I do not know about having to remove timing belt to replace water pump and dont have my service manual handy.

No, I do not do any off roading in this vehicle.

It can only be one of three things: your thermostat (already eliminated as the cause), your water pump (unlikely as it worked fine for a year after flushing and you didn't say anything about it making noise or leaking which are both symptoms of a failed water pump) and your radiator getting clogged (which seems the most likely cause to me).

Radiators should be flushed every other year because the fluid becomes acidic which leads to galvonic reactions which cause clogging of the passages. If this is the first time you flushed your radiator, that is a likely cause. Some radiators can be cleaned out (by unsoldering the side tanks and "rodding" them out - which just means they take a thin rod and push out the stuff clogging the passages). Many modern radiators are disposable (due to the use of plastics) and can only be replaced. I do not yet know what type of radiator your 4Runner has. Like hardened plaque on your teeth, this stuff can not be removed by flushing - it must be physically removed by pushing with a rod.

If you are a frugal DIYer and have more time than money, you can remove the radiator and run hose water through it to see what kind of flow you get. It should not back up at all. If it does, take it to a radiator shop to see if they can rod it out. I'm sure your radiator shop can test it for you too.

Ray

Thank you for the reply. I never really thought about that being the issue. If I remember correctly the radiator is a black plastic unit. This gives me something to think about at least. I guess it's possible it could be clogged or not flowing like it should causing the block to get hot and then the fluid boil/evaporate out. Is that the thinking?

It is the unit right in front of the fan. It has a fill cap on the top and many fins through which air flows to cool the water passing through it. You can't miss it.

The radiator is where the fluid dumps the heat. If fluid can't flow through it quickly enough, the engine can't dump the heat quickly enough and the engine overheats. The water pump (like your heart) is trying to push the fluid through the radiator, but it just won't flow fast enough to dump the heat. This is similar to arterial sclerosis in humans that leads to high blood pressure.

You are just waisting your time and money replacing the thermostat (again) and water pump (prematurely).

Diagnosis is the hard part of doing car work (I've done everything you can imagine on cars and engines including full rebuilds and restorations). Maybe you should consider taking it to a professional to get a correct diagnosis. It would be worth paying them something for their time and experience too.

Ray

The radiator is a Plastic and yes it happens to have black tanks top and bottom. I would check the flow as mentioned. Also remember if you do end up replacing it that the transmission lines also run through it too.

Here is a place that I used to buy lots of parts when I was restoring my Mercedes. They have great selection and used to have the best prices, but I have not compared lately.

http://sd.autohausaz.com/autohausaz/...40911@Radiator

This link was for a 4Runner radiator. They sell both all metal and metal/plastic radiators. I always prefer all metal when possible.

Ray

No, the fluid will not get too hot and evaporate out because the unit is sealed. The fluid can boil if not enough coolant is mixed in, then if you open the radiator cap, the steam will rush out and burn your face and hands while the fluid rushes out of the radiator. The simple thing would be to have a flush done. Also, there is a coolant reservoir that has lines labeled L and F. The level should be at or near the F line when the engine is cold. This reservoir is right in front of the battery. I recently noticed my reservoir level kept dropping over several weeks and finally found that the thermostat gasket was leaking, so you may have a slow coolant leak as well.

Well, The coolant is going some place then. I never have seen any leaks in the garage so I'm not sure that if after the engine and hoses heat up if maybe there is a small hole someplace. I'm pretty sure I have replaced the radiator cap once already but can' remember for sure now.

It sounds more like you have a blown head gasket.
You better get professional help with this one.

Ray

Just wanted to post an update to this thread. I dropped the 4Runner off at a local fixer up shop and had them diagnose. Turns out there was a leak in the radiator which they are going to replace. They will also be filling it back up with the Toyota red coolant. I didn't even have to mention to use that so I am happy that they are paying attention to detail. I will be picking it back up this evening. I will have them point out the area of the leak on the old unit when I pick it up. Thanks for all the posts, I just wanted to let everyone know the outcome. Only 69,000 miles on the truck so we should be good to go. Thanks

Good to hear it was a relatively minor problem as compared to a head gasket. I am surprised to hear that the rad was leaking at such low mileage though. Thanks for the follow up