I thought I'd best run this one by the experts on yotatech - the people here always seem to steer me in the right direction. The problem is with my 1990 4Runner 22RE. Please help me diagnose this one, thank you. I noticed coolant level going down ever so slowly yet originally did not see any noticable leaks. Originally thought it might be getting into the oil but thankfully that turned out not to be the case. Then eventually I noticed the very smallest of seepage happening where the upper rad hose connected to rad. Here is what I have done...

• Changed the hose - still small leakage there
• Changed the hose clamp - still leakage
• Checked pipe coming off top of rad for cracks etc - nothing found.
• Thought pressure in upper hose might be too high (at one point noticed some coolant spraying out where hose connected to thermostat housing) so replaced thermostat and rad cap - still small leakage where upper hose connects to rad.
• Did the 'funnel test' on rad to see if any bubbles coming up to indicate exhaust in coolant - no bubbles.
• Pulled upper rad hose half way back on upper rad pipe to expose as much pjpe as possible and clamped in place. Ran vehicle to see if could see where coolant might be leaking from that upper pipe. No leaking this time at all, however coolant started oozing out from under rad cap (this was a new cap).
• Repeated 'funnel test' on rad to check for exhaust building pressure. No bubbles although the coolant level did rise up a bit in the funnel when vehicle warmed up - perhaps this is normal?

i can't help but think there is a pressure problem here. Leakage at hose/rad connection, leakage at hose/thermo housing (one time), leakage at rad cap. Also, the vehicle doesn't seem to get too hot - gets up to halfway on the gauge and stays there. If there is too much pressure that forces the coolant out wherever it can, what could be causing it? Maybe it isn't pressure - maybe is bad connections (although I have tries to address all those). I almost ordered a new rad but not sure this would resolve anything. Any ideas before I take this thing to my mechanic?

 

Using a chemical block test would be a little better way to making sure headgasket isn't an issue.
But if the gasket was allowing combustion gases into the cooling system, and thus increasing pressure, I'd think the radiator cap should be releasing that pressure into the overflow bottle.

The radiator hose should be a fairly snug fit, before clamping. If the inner diameter of the hose is bigger than the outer diameter than the radiator connection then there's only so much a tight clamp can do. You didn't say where the replacement parts came from, but if non-oem it might be worth getting factory parts.
Pitting in the metal where the hose slides onto can be a source of seepage. The thermostat housing aluminum can often have pits. You can use a filler, like J-B Weld, then sand, to give the hose a good surface to clamp to. You don't see that often on the radiator necks, but worth inspecting. Are the radiator connections perfectly round, not slightly deformed/out-of-round?

 

Pitting, and the corrosion build-up that causes the pitting, can cause leakage.
Believe it or not, the clamp type hose clamps that are OEM work better than the screw down type. Also, the screw down type can deform the radiator hose fittings if screwed down too tightly. They can make the radiator fitting oval, and then it leaks.

The radiator cap is normally rated about 14 PSI, or one atmosphere of pressure. Doesn't sound like much, but it's more than you might think. Any more than that, and the pressure is released into the recovery tank. An increase in pressure as the truck warms up is perfectly normal. The metal of the engine surrounding the cooling system passages expands as it warms up. Since water can't expand or contract, as the engine warms up, the pressure the water is under increases. If you watch the level in the recovery tank, it will eventually rise as the cap releases over-pressure conditions, as designed.
Then, once the truck is shut off, and it cools, it contracts, and draws the water back into the cooling system through the radiator cap. You'll see the level in the recovery tank drop as the engine cools down. That's why it has a minimum level line. It ensures there's enough water in the recovery tank for the engine to draw in as it cools. If the water were to drop below the level of the hose in the recovery tank, it would draw air into the cooling system. Air doesn't cool the engine metal as well as water, which is the whole point behind "burping" the cooling system after working on it.
The hose in the recovery tank allows any air in the system that comes out the radiator cap to bubble into the recovery tank, and out. Any water flows into the tank, and, as required, into the radiator again.
Ensure the radiator cap is fully functional, with water able to flow out the large o-ring when the main portion of the cap is compressed, and back in through the small cap in the center. Make sure both portions of the cap are free to move as required.

Ok, I shut up now...
Pat☺

 

Thanks for the input and suggestions. What you are saying makes sense - the pitting or unsmooth pipe where hose connects could be what is happening to let seepage through. I did do a chemical test on the truck not too long ago and it was negative, however, maybe i should try it again (i have to borrow the tube from the auto store). It was strange when things started leaking under the rad cap - did'nt make sense to me becauase as you say you would think it would be going over towards the overflow battle.

i had recently put new hoses on (when I redid timing chain, oil and water pump etc). i believe they were dayco (rockauto). when things started leaking I went back to the previous hose for the top (although still leaking). I did check with toyota for a hose, however, they are $65 (just for upper) - and they can't get them anyways. i might try getting a different hose altogether - just called auto store and they do have an acdelco

 

Thanks. Yes, i'm thinking this pitting on the upper rad pipe might be the problem in allowing the small amount of seepage. It was actually the new rad cap that started doing that leaking. I will check it as well as the other parts you mention - hose to recovery tank etc. why/how that rad cap started leaking that one time is strange to me - as you say the coolant should be travelling over to the expansion tank (which it wasn't). i did confirm that the spigget/tube that goes over to expansion tank is clear between tank and rad cap.

 

Any part you get from a local parts store you have to assume it was made in China, or something close. And that often opens a can of worms. That’s why I prefer oem. That said, I’ll find it the cheapest place I can, which typically means online. I just build a list and order enough to make the wait worthwhile. I’ve even ordered parts from Amayama a few times out of Japan. Took a month, but saved a lot. Just have to price check.

I found that upper hose being sold by online Toyota dealers for $29-$32.
Toyota dealers will seriously mark up prices beyond MSRP for their walk-in customers, figuring they're desperate or impatient. Conversely, they'll drastically reduce prices online to access a broader market.

 

I guess it depends how badly I want a genuine toyota upper rad hose. My toyota dealer quoted me $65 but also said it isn't available. I can order online for $35+ online, however, being from Canada I then must pay almost that much again in shipping. Is it worth it - maybe

 

i mixed up some jbweld and brushed it on the upper rad pipe, sanded smooth, brushed on a bit more and sanded smooth. I have put the new upper hose back on. I am going to try and do the chemical test (tube and chemical) at the rad cap to triple check that exhaust is not getting into system and building pressure. If not, I will seal it up and see what happens. Is there anything else (besides exhaust) that would cause pressure to build? Water pump? Plugged rad? Anything else? I guess the thing is that if the pressure builds to high that it would release via the rad cap and out to the overflow. When it gets to that point is the pressure way more than it should be? Could I be causing damage if the pressure gets that high?

 

As long as gasses of some kind, whether exhaust, leakage from the cylinders due to a bad head gasket, or whatever, don't get into the cooling system, the pressure will climb up to a certain point, and then hold there, due to the radiator cap. You'll still get some coolant in the recovery tank, as thhe metal of the engine will expand far enough to build the pressure to 14 PSI, and then a bit more, forcing the radiator cap to release some fluid. Then, once the engine is shut off, it'll draw back down to the point it began. Once all the air is bled out of te cooling system by burping it, or even just running it, the level in the recovery tank shouldn't change. It will increase during the running of the engine, then return to the level it was when the engine was first started cold. It should pretty much stay there.

Other than all that, no, it shouldn't get any more pressure in it. Or volume. Te system is designed to function at peak efficiency at 14 PSI. It raises te boiling point of the coolant somewhat. As the engine temperature varies, the pressure in the cooling system will vary also. As needed it will release, or draw water in from the recovery tank.

 

thanks again. If I do the chemical test for exhaust and the result is negative can I be quite certain that the sporadic leaking I am experiencing is not related to pressure but only to bad/weak connectuons.

 

Probably the shortest answer I ever gave: YES.

Pat☺

 

chemical test complete. Negative result. I guess that is good news. Is there a possibility that a water pump/water circulation issue could be causing some of these leakage problems - not circulating the coolant properly? If so is there a way to confirm coolant is circulating OK.

 

So far, you've only mentioned some visible seepage and coolant level dropping in overflow; but nothing about the temp gauge reading higher.
A restricted radiator, faulty thermostat, or defective waterpump would typically manifest first as an engine running hot with a higher than normal temp reading on the gauge.
If the gauge is reading fine than you need to track down any possible external seepage.
Around hose clamps is a good place to look, and you have a bunch of water piping under both manifolds.
One possibility is a slight seep at the head gasket, but externally down the block. If the seep is slight enough it could be steamed off by a hot block before it drips off to the ground. The stain on the block will be very obvious.

fwiw, I always wished Toyota would get a tool to measure waterflow that could be installed in-line at one of the radiator hoses. We could block-test the headgasket, replace thermostat, and inspect waterpump. but if all those passed and we still had a hot engine the radiator would be the next culprit, but not really by any test, but a process of elimination.

 

my temp gauge is may be showing a little warmer than typical. To be honest i am forgetting somewhat what typical was. It is showing about half on the gauge which I think is fairly typical.

 

Only way I know of is to leave the radiator cap off. Once the thermostat opens, you can see the coolant flow past the radiator cap hole increase a lot. You'll be able to see the rate of coolant flow. Be aware that as the engine warms up, the water in the radiator will rise and overflow the hole before the thermostat pops. It gets pretty warm, too.

Alternatively, the temperature of the drivers side end of the radiator top tank should increase suddenly, once the thermostat pops. Iff it doesn't rapidly heat up, the flow is low.

Check the weep hole under the pulley of te water pump. If there's much leakage, the water pump is, or is going, bad.

Does all that help?
Pat☺

 

Half way is fine. I’m sure it read lower at one time when the radiator was pristine and more efficient at heat exchange.

what has bitten more than one 22R# owner is the double lower radiator hoses. It’s not uncommon to see one replaced, but not the other.

 

Thanks for the tip Pat. I removed cap, drained a small amount of fluid so it wouldn't overflow and started the engine. As the engine heated up i watched the surface of the coolant at the top of the radiator. Mill pond - no movement.. Once my gauge went up to just below half, still mill pond. I gave the upper rad hose a little squeeze and then i saw flow beginning. The flow went from left to right (away from the upper rad hose). It flowed across for maybe 10-15 seconds then seemed to stop. I watched a few cycles of this happen - would start to flow from left to right (away from upper hose) for about 10-15 seconds (not super fast or anything), then it would more/less swirl in place for about 10-15 seconds and then would flow right to left (towards the upper hose) for 10-15 seconds and then stop. Is this telling me anything? Is any movement good movement? upper hose quite warm, lower hose not. Temp gauge did not go too high (beyond the half). To recap, the water pump is new and the rad itself is original. I have also tried a few new thermostats to make sure there is no problem there. What do you think Pat, anything to be concerned about?

 

Hmmmmmm!
From what I've seen personally, the flow should be consistent, away from the upper hose. Once the thermostat pops, the coolant should flow across the top tank of the radiator, upper hose to lower hose. The thermostat should be opening at about 1/2 way on the temp gauge.

I've never seen it flow backwards, though.

Having said all that, though, as long as the temp gauge isn't going much above 1/2, the system must be functioning tolerably well. All this is right at initial warm up, however. Does the fan make the "whoosh"ing sound right when the engine is first started, for 30 seconds to a minute, approximately?
Once the thermostat has opened, you can reach up and run the RPMs up a little. That may well settle the flow down, and speed it up a ways. IOW: increasing the RPMs will cause the flow past the radiator cap to increase. Probably make it more consistently away from the upper hose to the lower, too.

None of this all should have much effect on the loss of coolant, though. As Jimkola mentioned, there may be a small leak behind the visible portions of the engine, and it gets evaporated off before it can drip onto the ground. Also, there may be a slight leak from one of the small hoses under the TB and intake manifold. I've seen leaks develop in the solder joins of the short tube the radiator cap screws down on, too. The coolant leaks slowly, and gets evaporated off the surface of the radiator tank, before it can drip onto the ground. The main sign it's leaking there is the paint on the top tank comes off around the cap.
Finally, quite often, when working on the cooling system, draining and refilling it many times, air can get trapped in the system, even with the best "burping" procedures. As the truck is run, the air can, and will, bubble out, causing what appears to be a loss of coolant. I don't worry about loss of coolant, especially a small loss, for about a week or two of consistent operation. Fast and slow, in traffic and out, and so on. I just keep topping the recovery tank as required. THEN, if the level in the recovery tank is still dropping, I start looking for loss points.
Remember to check the second lower hose, the short jumper, U-shaped, hose between the transfer pipe and the inlet to the water pump. It is just as important, and likely to leak, and is the same size, as the other two big hoses. It should be replaced at the same time as the other two as well. Check the transfer pipe for leaks every now and then, too.

Keep us up to date. This getting frustrating
Pat☺

 

Once the thermostat opens you can actually gently squeeze down on the upper radiator hose and feel water circulating, including any air pockets that are passing by.
if the radiator had restricted passages you can often feel “colds spots” on the radiator while the engine is running. The radiator feeling a bit cooler from top to bottom is proper, but if you move your hand sideways along the surface and find pockets that are noticeably cooler that usually means that row/fin has issues. If the fan clutch isn’t locked up you can easily stop the fan blade from spinning while you do this.
But if your vehicle isn’t overheating, and you’re simply seeing the overflow go lower over time, I wouldn’t spend too much time on internal concerns. You passed block test, and your temp gauge is considered normal. Maybe go borrow and radiator pressure kit and pressurize the system and see if it drops, and how fast.

 

The advice I get on here is fantastic. Some months ago you guys lead me through the diagnosis and subsequent replacement of timing chain, cover, water/oil pumps and a number of other related things and now assisting with this. So good. Anyways, the coolant leak on this thing was very slow and perhaps it was from that bit I saw leaking around the upper rad hose/rad connection - which seems ok now that I smoothed out that upper pipe coming off the rad with some jbweld and sand paper. I got onto this idea on whether coolant was flowing ok because i thought that maybe excess pressure was building and was maybe because lack of flow. Perhaps it isn't a problem, however, I have fired up the engine again to watch the flow and revved engine a bit as suggested to try and see a more noticeable flow inside the cap and to be honest I'm really not seeing any flow to speak of. The coolant is pretty stagnant in there even when i watched it right through the period of rad still cool to the point where the hot water obviously came over to the rad (and hose/top rad got very warm). but no real noticeable flow at all past the rad cap. As suggested by Jimkola will see if I can feel any cool spots on the rad - will try again once things cool down. Also, both of you have mentioned a second lower hose - I do not remember such a hose - as I recall there was just the upper (passenger side) hose that i replaced and the lower (driver side). There is another u-shaped hose of same diameter? I better look for that one. oh, i guess it is the one to the water pump.