1UZ vvti overheats at speed. Things to check?

[George_R]

Running 1UZ vvti off '98 celsior, ~60k' s on it. Timing stuff replaced (belt and everything), water pump also replaced with toyota original unit just incase. Old WP was fine though.

Radiator is brand new aluminum aftermarket unit, the biggest one I could fit. Sized about 600x450x60mm. Using original Celsior hydro fan with no shroud. Temp sensor for the hydro fan control is installed into a metal pipe that connects bottom radiator outlet to thermostat housing. The sensor itself is very close to the radiator outlet.

Thermostat: haven't yet replaced it. Using red coolant.

The problem is: I was driving ~700km the other day and it was fine all the way. Diff ratio is 4.1, there's ~3500 RPM @ 140kph. Gauge temp sensor was consistently showing the normal temp.

On the next day however I suddenly noted that in the very same driving conditions, the temperature reading suddenly went up. I slowed down to ~100kph and it went back to normal. Tried that several times, and each time I had to slow down to bring the temp back to normal.

Later on I had to spend ~4 hours in a stand still traffic jam and the temp was ok.

It's the first time for ~6 month of running the engine in my conversion project when I experience this problem.

What I plan to do is replacing the thermostat and bleeding the system properly. Maybe I can have some advice here? Previously, I just filled the radiator, open its cap, filled the overflow reservoir until it drains to the radiator and that's it. Only checked the reservoir level a couple times just to find it at previous position.

I've just read somewhere on the web that I must get the engine as cold as possible, and fill it with coolant thru the hole on the throttle body, having its bolt (inverted hex one) unscrewed. (my engine is like that of 98-00 LS400, and I've read that these engines are bled through the throttle body bolt). Is it true that otherwise the system will not be bleeded properly? Does it also mean that if I never done this procedure I was always driving with some air in my coolant system, but somehow I never seen overheating?

 

[George_R]

p/s
searched the web a bit more. I think this topic is relevant so I'll add it to my thread in case someone else comes across it having the same troubles as I do
http://www.clublexus.com/forums/per...397401-car-overheats-only-at-high-speeds.html

 

[cribbj]

George, this is the 1st I've heard of getting the engine as cold as possible before bleeding.

Normally we want the engine as hot as possible in order to ensure the 'stat is fully open. Then we bleed from the highest point in the system.

I realise the 'stat for the UZ is on the "inlet" side of the engine instead of the "outlet" where it usually is, but this shouldn't impact the theory of bleeding, and making sure the 'stat is fully open.

I would 1st bleed the system, then if there's still doubt or you're still having problems, change the 'stat.

 

[Zuffen]

Agree with John.

Bleed it hot and from the highest point.

It doesn't sound thermostat related as it runs cool when moving slowly.

The lack of fan shroud and using the sensor in a different spot are the main deviations from stock so probably where I would start looking, but these should affect slow/traffic running more than higher speeds.

Shouldn't the hydro fan should be sensing temp via the ECU.

 

[George_R]

Update
The bleeding port hex stub appears to be completely stuffed. It'll took quite a while to find a replacement one and unscrew mine. I'll also have to undo the hydro fan to be able to undo the t'stat housing due to tight fitment.

cribbj
I've already bought one, so the new 'stat will ultimately go in. I've read some reports that changing the 'stat in an imported 1UZ vvti conversion helped decrease warm-up time in winter, so apparently mine can be less than perfect, too. And it only costs about $20.

Zuffen
Celsior's (UCF21) cooling system comprises of sensor, fan, pump, control valve and ECU. Some of its features are weird to me, however it works perfectly in slow traffic, the fan is quite compact and fits nicely. It doesn't kick in and in most cases it's operation isn't apparent, very contrary to a generic electric fan. There are devices available for smooth operation of an electric fan , but I find their reliability less than optimal.

Back to factory cooling system. The sensor is actually mounted in the radiator very close to A/T cooling route. It's even described as "oil temp sensor" in parts catalog. However the a/t already has one.

This sensor is ultimately used for operating the hydro fan. Fan speed is controlled by fan fluid cutoff valve utilizing PWM technique. Celsior's ECU would output code 56 when it doesn't see the valve or the additional sensor. Unlike earlier celsiors however, the presence of the code would not affect engine performance.

Back to my problem, I guess that the lack of shroud is ok as I've never ever seen the temp needle move in slow traffic. Next thing that assures me is that the radiator I use is surely overkill, and you can feel by hand how it gets increasingly colder from top to bottom.

 

[gloverman]

I have seen some alloy radiators block up after a short period of use. Sometimes caused by stray voltage.

 

[George_R]

Interesting! But if it was blocked indeed, I assume I would see overheating consistently? Not only at high speed?

 

[George_R]

Still feel it's something wrong with it. Filled up top of the throttle body, replaced the stub, then filled up to top of the radiator and to the overflow bottle. Tried driving with heater on, but after stopping and restarting the engine the dash needle dropped a fair bit. So I assume some air is still caught in the cooling system and I have no idea how to let it out.

 

[gloverman]

sometimes blocked radiators only overheat as more load is applied. We fix plenty of vehicles that drive fine until a trailer is attached.

As for the bleeding have you checked the radiator cap is OK? I have also seen a dodgy radiator cap cause similar issues. Did another car recently and after fitting a genuine radiator cap it's issues are sorted. During the owners time he has replaced the radiator , cylinder head and waterpump but never the radiator cap.

 

[George_R]

Well the radiator is an aftermarket part. The cap came along with it and I don't know for sure if it's ok or not. It says it's 0.9 bar which is about ok for Toyota (from factory pressure must be 0.7 or so as I can recall). I have no idea if some original cap would fit the radiator as I've never seen a complete donor )

I'll post a couple pictures just incase. Maybe you'll see something wrong about it. As shown, the radiator top is well above engine top, pressurized is everything but the overflow bottle.

 

[gloverman]

I see the issue. The brake booster is on the wrong side.

 

[George_R]

It's weird you didn't notice it's upside down either

 

[George_R]

After s few cycles of warming up and staying off long enough it finally seems to have been burped. Gauge temp stays where it's supposed to; ran diagnostics to see EFI temp. It shows 87 steadily after warm-up. Ordered a new Gates universal radiator cap that's supposed to mechanically fit (0.9 bar)

Suddenly noticed that long term fuel trims are way too high (+14% and +18%) for some reason; didn't run diagnostics for months so I don't know for sure when did it start. Positive trims is clear indication of some failure but that's the topic for another thread

 

[George_R]

cooling wise, I think I've found the problem. Leaky freakin chinese cap that came along with the radiator. Was leaking from the top under sticker.My new order arrives soon, will see how it works.

As for the trims, I'm inclined to think it's mostly due to dirty injectors and/or dodgy plugs as the trims are different on banks 1 and 2 (both being too high).

 

[gloverman]

Good to hear you have found it.