Truly stumped, 05 Tundra over heating

Hey all,
I’m hoping to get some advice about over heating and over boiling on my 05 Tundra 4.7 V8. Because I’m truly stumped as to what has been causing it. About 2 weeks ago I had a crack develop on the top of my radiator, this obviously caused overheating, thankfully I was able to limp it home without the temp gauge get to the red for more than a second or two, before having the ability to pull over. I wasn’t able to get the truck to my regular repair shop, booked 3 weeks out.. So I brought the truck to a friend of a friends, that replaced the radiator.
This seemingly went smoothly and there were no issues until I began to overheat again about 200 miles later. Neither myself or the radiator replacer have been able to figure out what’s going on. I’ll be able to idle the engine and even keep it at a high idle ~1500-2000 without it over heating or over boiling. But when I start to drive, after about 15-20 miles the heater cuts out then I start having a rapid increase in temperature. My reservoir starts bubbling and it overflows causing me to loose coolant. This seems to be the only source of coolant loss.
I initially thought this was something simple, radiator cap, thermostat, air lock in the system. So, I replaced both and have attempted to burp the system multiple times, I got and (still get after boil overs) a bunch of air out but otherwise there wasn't any improvement.
This lead me to start thinking about a blown head gasket, I did a hydrocarbon block test and cooling system pressure test, both were negative. No missed cylinders, no milky oil, milky coolant, or residue on oil cap.

So some, clarifying things and questions

The coolant/radiator does not bubble until the engine begins to heat up to a working temperature and is under pressure, there are no bubbles when the cap is off and the engine is running.
There is also negative pressure on the system after the engine cools down completely, the hoses are sucked in and compressed. Does this with the CO test and pressure test exclude head gasket leak?

No other issues with the truck, it runs exactly like it should until it starts it’s latest.

There seems to be a coloration with downshifting and a decrease in engine temp. ie. shifting from D to 3 when the engine is starting to over heat causes it to cool down rapidly.

It seems like its getting circulation through the system (looking through the top with the motor running) but the radiator will transiently have cool spots and the bottom of it can be significantly cooler than the top 180’ vs 90’. Should I flush even though it’s new radiator and fluid?

The fan clutch is definitely not loose, if anything it’s almost too tight, only rotating 1/2 - 1 in when I attempt to spin it. Is that too tight, is that possible?

I would really appreciate any insight or experience before I have to go through what I’m thinking would be an expensive diagnostic.

 

That's a wall of text, so sorry if I missed something. Thorough is good and all.

Really stupid question here, mainly because your t-stat is mechanical and thus should open at a given temp if it's the correct t-stat and you clocked it correctly on install and your water pump is actually working (how old is it?), but ...

If my last statement is accurate, and it's also boiling over, that would suggest the mechanical t-stat is either not doing its job, or something is clogged somewhere. Can you tell us what color coolant you've used in the truck, and whether you've ever mixed colors, at any point?

Since it's boiling over, I'm going to assume things are actually overheating, and this isn't a case of a bad temp sensor. If it wasn't boiling over, I'd suspect the temp sensor was bad, or the wiring to the temp sensor was compromised. Happened to another member this week.

 

Where’d you get the new radiator? OEM? Sounds faulty if it has hot and cold spots on it.

 

Maybe just a shot in the dark, but I would pull the thermostat and make sure its working properly by dropping it a pan of hot water. Simple test, and it will rule out one of the parts to your overheating puzzle. Good luck.

 

What radiator did you use? The only ones that are proper are OEM, Koyo and Denso.

The others have a core that is way too small for our trucks.

Did you reinstall the shroud and the lower piece of it that clips in?


What brand thermostat?

Sucking hoses in like that is a sign of air and that the cap isn't allowing it to draw from the reservoir.

 

Man, water pump sounds fun to change out if it’s the problem. hopefully not too old and was replaced during the last timing belt change.

OP, here’s my caveman ideology. Initially your problem was a cracked radiator which was evident. You replaced it with a new one and are experiencing the same problem. It may be logical to assume that it is not functioning properly. In that 200 miles you drove, the likelihood of another part failing related to engine coolant is slim.

 

+2 on this. The cap is not allowing the cooldown process to restore the expelled coolant when the normal heat up process is at full bore. Repeat this step over and over and the system ends up low on coolant and overheats more.

I'd suggest OEM on the cap. Once replaced and system is 'full' per overflow tank watch what it does as it heats up and cools down, make a mark so you know what is 'normal' from day to day.

The fan clutch can also be suspect with that age. Look up tests for it to be sure, it may not be pulling enough air when underway driving around.

 

could it be a bad thermostat? Or installed incorrectly?

 

I'm thinking it's the thermostat not being aligned correctly to allow air to escape when it was installed. Pretty much what @shifty`was asking about it being clocked correctly.

 

Could the cap not be seating right in the radiator? I've had a cap break and coolant would boil in the expansion tank. Wondering if maybe whatever brand rad you bought isn't right where the cap seats and it's not seating properly.

 

I'm voting cap too. If it's not keeping pressure on the system it'll let it boil very easily. Or bad cap housing on the replacement rad.

 

You might want to to monitor the transmission temp while you're troubleshooting. Did friend of a friend top off the ATF after replacing the radiator?

 

Do we have hump day polls…

A: Thermostat and/or installed properly
B: Radiator and/or Cap….OEM only
C: Shrouds installed
D: Proper coolant/mix

 

I appreciate the read and the response I am not actually sure how old the water pump is and thats why I'm suspect of it too. Though it seems like there is circulation happening when the engine is at idle or warming up. Do you know of any other way to test the pump other than looking in the top of the radiator?
I did end up mixing colors when the first overheating happened with the radiator crack, I couldn't get any toyota specific when I was leapfrogging gas station to gas station buying coolant. Since the coolant has been the OEM spec, Im planning on doing a complete flush and blow out (some how) today to address the potential clogging.

 

I'm not sure where the radiator came from, the guy that put it in got it. Im going to try to find out, is there a way to test the flow in the radiator. I was planning on pulling out the bottom hose of the radiator and sticking a hose in the top to see how it does coming out the bottom.

 

Thermostat is a duralast from autozone, OEM temp. With the hole at 12 o'clock.

 

So initially this guy, might be useful to mention this guy is a bit crazy and maybe a shady mechanic. Had put a generic radiator cap on the newer radiator, when the overheating began to re-occur I got an OEM cap. After reading this comment I looked at the threads of the radiator attachment. It looks like it has been somewhat stripped out.

If it's possible could you take a couple detailed pictures of your radiator opening with the cap off? I want to compare a rad that isn't overheating with the opening on mine. Potentially this could be the wrong radiator/ or the radiator threads are stripped out not holding pressure. It would be super helpful!

 

If nobody gets to it soon I will around 530 or so.

 

Hard to see tbh

 

It has to be something simple (says the guy who can't figure out his brakes)

I hate to just throw money at it, but I would be tempted to buy a OEM thermostat and Denso radiator. Do a full coolant flush including draining the two plugs on the bottom of engine block. I've heard of brand new thermostats being faulty.

Forget the shady mechanic and do it yourself. If my dumbass can do it, so can you.

 

Waterpumps either work or they don't, there is no in-between. When they don't work, they leak after a hot engine shutdown. You'd know this already if it were happening by the puddles. Get an OEM cap first, they one you have should let coolant out under appropriate pressure and then allow it back in as pressures drop, anything less is faulty. Luck.

 

Yes get the cap first
Process of elimination! Start with the cheap stuff before you start forking over big bucks.

 

It literally could be one of everything that has been mentioned.

I only run OEM stuff Duratrash has me concerned. OEM thermostat should be clocked properly to vent. The impeller on the water pump is some type of composite, but I’ve never heard of the impeller failing.

Radiator cap should also be replaced with OEM.

I’ve never had any issue with air pockets or bubbles in either of my 2UZ’s. And that includes multiple coolant system drain and refills.

Before I even read anything I was thinking head gasket, but sounds like you already checked that.

 

Are you sure you’re only loosing coolant from the reservoir?

 

@sendit_allday Is there a resolution to this yet?

 

@sendit_allday
take it out back by the old shallow grave?

mines on 2nd new radiator in 1 year and just starting overheating again..
slow leak at water pump..
only warning i get is no cabin air heat.. will blow cold air until it reaches oper.teno and give full hot all at once..
new tstat last radiator, checking on brand of rad, last one was junk, unsure of radiator cap..
coolant persistent slow leak at water pump and let it get too low with explosive results.. trying to fill it up and burp the system without blowing another rad..

any results with yours?

 

the temperature sensor and the heater core circuit are both located fairly high in the cooling system and letting your coolant leak to the point where you're about a quart low seems to result in a pressure spike, no coolant in the heater core, and perhaps some monkey business with the thermostat as well..

i added a quart of coolant and gas pedal buroed the system to ensure water pump operation. (oulled over, let it cool, opened cap, filled the rad, filled the ressi, and let it run..

filling the resevoir did not fix it, temp was still bouncing all over, had to let it cool and open the cap..

your cracked radiator was caused by the pressure spike..

you have a slow coolant leak somewhere, (mine at pump gasket) be dilligent about checking levels..

hope your trucks okay!

 

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