last weekend i drove the runner for about 45 minute long up and down hills autobahn drive 60-75mph the whole time.
when I returned home i noticed a coolant smell and looked and found the overflow bottle had purged and was full but the radiator was low. the truck NEVER overheated but it had pushed the coolant out. not coolant in oil and no oil in coolant. head gasket has about 1000 miles on it and looks good.
What could the cause be? thermostat not opening?
Thanks
david

If you call an ugly Harley a rat would my ugly 4runner be a waterbuffalo?

 

Had the same problem on a 75-80mph, 5 hour, run to Cornwall Last weekend. I've changed my reservoir supply/return pipe about 10 months ago due to this problem and so will check to see if the return gets blocked in any way.

If you find a solution let me know and I'll do likewise.

 

Time for some team work!
I will check the lines tonight.
David

 

Is there a way to drain out the reservoir supply?

 

12mm socket, loosen the bolt holding the resovoir and pull it out,
remove the cap and pour it back into the radiator.. Viola refilled!
lol
david


easy to do just get tired of doing it!

 

3 foot long hose pipe and puckered lips!

 

sorry but there would be no gravity feed into the radiator that way!!!
more like suck spit suck spit suck spit etc, etc
David

 

Yes if you want to put it back in the rad, BUT the question was: "drain out the resevoir" - and I did that, onto the tar, with a hosepipe just last week.

 

Wouldn't the overflow be caused by driving up and down hills? Since your trucks are not level when driving, the fluid in the radiator is reaching the level of the hole for the overflow tube and going straight into the overflow bottle. And since the overlflow bottle does not have a return line back to the radiator, the amount of coolant in the radiator decreases.

 

My understanding is that as temp increaseases the coolant expands and therefore pressure increases. As pressure and volume increase so coolant is forced up and out to the resevoir. Then, as the cooling system decreases, the volume and pressure decrease causing the coolant to be drawn back into the rad by the vacuum the cooling creates. N'est pas?

 

the cap on the radiator is a pressure releasing cap wich means that it will keep the fluid in the radiator untill the pressure is reached to let it purge (i think around 18psi) Has nothing to do with level of the truck. but if this is true there is no way for it to return wich inturn makes the can at true catch can. it catches the purged fluid so there are no dead puppies. I need to look at it tonight and see if there is a way for it to return.
David

 

Someone in South Africa told me you could screw a pressurised "bottle"/"expansion tank" into the existing rad to increase the rads volume - true?

 

Aside from what Bundubasher said, I don't know the science of it, but I can assure you that the cooling system will draw coolant back in as it's required... due to my leaky thermostat gasket I can watch (throughout the week) as the reservoir level drops.

Perhaps replace the pressure cap... a faulty, blocked or incorrect (non-pressure) cap won't do any good either.

Also, if there was a leak in the reservoir pipe or cap then that may stop it all working correctly due to lack of pressure?

 

Hell man! I replaced the thermostat and the rad cap at the same time as the resevoir feed tube and lid. Personally what David says makes sense - if you have an open return path for the coolant to pass backwards and forwards along then the rad would not pressurise. Anyway why do they pressurise water? Water that is under pressure boils faster than water that is not - any climbers on the forum should know be able to comment on that.

 

ok looking at it just now, if the radiator pressure has gone down the cap is then sealed and then there is no way for it to return.

except by osmosis.
lol
david

 

Actually, it's the other way around. The cooling system is pressurized to raise the boiling point of water. Here's some more info: http://science.howstuffworks.com/question63.htm

 

Robinhood is right. The higher the presure, the higher the temp you need to get it to boil. I live at 4300 ft and it takes less time on the burner to boil water due to the altitude diff.

I haven't taken my radiator cap off and looked at it supper close, but my overflow tank looks like it should allow the movement of fluid back into the radiator when it cools. Thats why the tube goes all the way to the bottom.

It sounds to me like you got so warm that you let more fluid out than your bottle could handle. I wonder if you hadn't pulled your tube all the way out, would it have sucked fluid back in to try to equilize presure.

Oh, one other thing. The cap releases at a certain positive presure, but negitive presure is just as "strong" so I would think it would open back up to deal with the negitive presure of cooling steam. Just my .02

 

Excellent! Many thanks for correcting my error - I'll just have to go on puzzling this one though (and so will quite a few others too) until I reach a satisfactory conclusion. I understand that by adding an ARB bullbar I am #1. adding a lot more weight to the front of my vehicle and #2. blocking the rad's free airflow to some extent. Obviously since the vehicle was not designed for these additions it doesn't quite cope with them.

What about enlarging or replacing/adding to the existing rad? Anyone got any thoughts?

 

but there is no way for it to direct the fluid vrs. the air back into the system, the cap has a positive seal and it cannot choose what is drawn in.
David

ok.
I maby wrong on this because the cap has a double seal one befor the overflow point and one after (more of a positive seal not effecting the spring seal)

 

I have a 1st gen. 4Runner, so I don't know what your radiator cap looks like, but I checked mine out yesturday, and I have a small hole in the lip that my cap attaches with a hose that goes to my over flow bottle. I noticed I hadn't checked mine in a while, so I filled up my over flow bottle, went for a drive, and when I checked again after work, my bottle was almost empty. This shows that fluid was pulled back in by the presure, becuase my bottle doesn't leak and the true over flow hose off the bottle wasn't at all wet.

Like I said, could be totally different for the later years.