strange situation i was wondering if anyone can help with. i just changed out my radiator on an 08 v6 due to seepage on the bottom of both tanks. i used a denso from rock auto & the install went great, fits perfect. all hoses were in good shape so reused them. used zerex coolant & did not drain the block, plan to do a drain & fill in a couple weeks with a 2nd gallon & the fluid i changed out looked great, probably changed at some point before i bought it.

now on the first few drives only the passenger side tank is getting hot after 20-30 minute drives in town stop & go. the tranny lines are warm on the driver side & the tank is slightly warm around the tranny lines due to the trans cooler in the tank. also the lower radiator hose is cool but both hoses build pressure when it warms up & the gauge reads where it always has, right in the middle.

i didnt notice any big air burps when filling the radiator but did squeeze the hoses as i filled it. the coolant is full in the rad & the overflow jug is half way between the lines.

does this sound like there may be air trapped in the tank? or the thermostat isnt opening? or does it just take that long to fully warm up both sides of the tanks? if anyone has a chance when they start & drive from being cold, can you pull over after about 20-30 minutes of city driving to feel the tanks & let me know if this is normal? i will drain & fill the rad again asap but i did loosen the drain plug a tad & fresh coolant comes out so its getting over to that tank... just takes forever to warm up & even then its cool compared to the very hot passenger side tank & upper hose. ive changed radiators on many other vehicles before & never had this issue.

Something isn’t adding up.

Please provide this information:
- what did the radiator tanks feel like before you changed the radiator?
- what does the instrument cluster gage read for water temp?
- what do you mean by both tanks are not getting hot? What does not mean by your definition?
- have you run the interior heat at the highest temp and fan setting? What did you experience?
- did you open the radiator cap? What did you see?
- is the de-gas bottle (burp tank) full?

I just got off the road from 2.5 hours of highway driving at 75mph pulling a 3,300 lb boat. The radiator should be smoking hot, right? It isn’t. Both tanks are warm, arguably very warm. But not hot. I can touch them with my hand for as long as I like. Temp gage is dead in the middle between C and H. Burp tank is full. Radiator cap when removed shows a brim full radiator. Interior heating functions normally.

Please provide more information and post your findings.

- sorry didnt think to feel the tanks on the old radiator, thats why im asking others to feel theirs after a 20-30 minute drive.
- gauge reads halfway between cold & hot as it always has.
-didnt say "both" tanks are not getting hot, just the driver side. pass side gets very hot within ~15 minutes. driver tank & lower hose are cool after 30 minutes.

-yes, heat gets hot as normal... but temp & fan settings dont matter for coolant flow, coolant fully runs through the heater core regardless of fan/temp settings.
-i opened the rad cap & coolant is full to the top.
-overflow bottle is filled properly between the 2 lines.

thanks for the reply, maybe you didnt read the whole post but most of what you asked is stated in there. does any of the new info you asked about help anything?

im mainly looking for others to confirm what their driver side tank does after a 20-30 minute drive, which in 80* temps should be long enough to fully warm up both tanks. or thoughts on if it could be trapped air.

Thanks firebirdguy. Your vehicle seems to be functioning normally. There might be some calibration needed on what “normal” temperature of the radiator tanks is.

I just again got off the road from driving 2 more hours in 73 degree temps pulling a 3,300 lb boat.

Top hose that feeds passenger side rad tank hot.
Passenger side rad tank very warm.
Driver side rad tank warm.
Bottom hose which drains the driver side rad tank slightly warm (not as warm as the corresponding tank).

The radiator rejects heat across its width (face). It is normal for the two rad tanks to be unequal temperature. It is normal for the passenger side tank to be warmer than the driver side rad tank.

The interior heater test tells very clearly if a low coolant situation is in play.

ok thanks again. i havent driven for a long trip yet or on the highway. just did a couple short drives to check for leaks, then did a 30-45 minute low speed stop & go in town drive last night & felt the tanks after idleing for 5 minutes at a drivethrough... driver side tank still very cool, barely warm & mainly only in the center where the trans cooler lines hookup. bottom rad hose barely even warm, especially compared to the hot upper hose & pass side tank.

interior heat is great so i know its circulating through the heater core, just figured the driver side tank would at least be noticeably warm after 30+ minutes of driving.

all other cars i own or have worked on warm up the entire radiator pretty equally after the engine reaches operating temp & the t-stat opens.

new radiator is still doing good but still amazed at how cool the driver side tank & lower rad hose is. went for about a 45 minute 20 mile drive & in 75* temps its still not fully warmed up compared to the pass side tank & upper hose.... its darn near the same temp as outside!

maybe this is just how efficient the radiator is or it takes a loooong time to fully warm up the rad?

is anyone able to check their driver side tank & lower hose on a 30-45 minute drive? curious what other 4runners are like.

You want it to be cool... It's a radiator it cools your engine.

Hot flows in the passenger side, it's cooled, cold goes out the drivers side.

Hi firebirdguy,

Your vehicle appears to function normally.

I just did a test that meets your specifications.

Starting temps:
Ambient: 81 deg F
Temp gage in cluster: C
Engine: cold/ambient
Drivers rad tank: cold/ambient
Trans cooler lines: cold/ambient
Bottom rad hose: cold/ambient
Passenger rad tank: cold/ambient
Top rad hose: cold/ambient

Ending temps after 30 minute drive:
Ambient: 81 deg F
Temp gage in cluster: between C and H
Engine: hot
Drivers rad tank: barely warm
Trans cooler lines: warm
Bottom rad hose: barely warm
Passenger rad tank: hot
Top rad hose: very warm/hot

Hi firebirdguy,

Your vehicle appears to function normally.

I just did a test that meets your specifications.

Starting temps:
Ambient: 81 deg F
Temp gage in cluster: C
Engine: cold/ambient
Drivers rad tank: cold/ambient
Trans cooler lines: cold/ambient
Bottom rad hose: cold/ambient
Passenger rad tank: cold/ambient
Top rad hose: cold/ambient

Ending temps after 30 minute drive:
Ambient: 81 deg F
Temp gage in cluster: between C and H
Engine: hot
Drivers rad tank: barely warm
Trans cooler lines: warm
Bottom rad hose: barely warm
Passenger rad tank: hot
Top rad hose: very warm/hot

The temp gauge does LITERALLY NOTHING. Don't rely on it. The only time it will move is when your engine is on the brink of getting destroyed.

Your replacement summary sounds fine, I wouldn't worry. Drive it, come back and let it cool and fill as needed. You're fine. Get a $10 bluetooth OBD2 scanner and look at coolant temps if you're worried, but sounds fine.

yes im aware its a radiator etc etc. however on every single car i have owned or worked on, & thats quite a few- stock daily drivers to high performance muscle cars, the entire radiator & both tanks/hoses are very warm/hot to the touch after a 30+ minute drive to operating temp & the thermostat has opened. if you used a infrared gauge on both tanks there would be a difference but the bottom hose & opposite tank are too hot to touch in a very short time.... not almost cold like the 4runner radiator is on one side. so i just wanted to ask about it & see what other 4runners do.

im not relying on the temp gauge, just pointing out that its at the normal operating range when i checked the radiator tank/hose by hand.

maybe your 4runner is different, but my gauge does LITERALLY SOMETHING. it will gradually climb off the cold mark as it warms up & fluctuates a little in different driving conditions such as towing or sitting at a drivethrough for a long time in hot temps etc. it does what its supposed to without the engine being on the brink of getting destroyed.

im not really worried about the coolant temps but i will check them with a odb scanner i have. the only concern was the huge difference in the two tanks & hoses.

thanks chassis! that is perfect.

that confirms that this is a normal thing. i should have checked the previous radiator but never thought about it & never had a coolant temp problem, just a leak i wanted to fix asap.

thanks again for the help!