1UZ cooling system questions / issues

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Mat Grant

Member
Messages
143
Location
southern UK
Hi all,

Finally got my build running, 1UZ into a 1979 Lotus eclat. After a very long time of fabricating, designing, building, electrical systems, and making a full custom wiring loom it started first click like a new engine.

BUT - I'm having trouble with the cooling. The engine starts and runs perfectly, revs ok, and idles nicely, starting about 1200 ish rpm, once warm idles at about 700rpm. No error codes on the engine.

I've got a different temp gauge so I'm not sure of the calibration with the 1UZ sender, but the engine warms up and the ECU obviously thinks the engine is warm as it slows the idle to the 700rom idle speed. The gauge shows 80 and up to 90 when running and warmed up. I've not run it continuously for a long time as I'm not convinced about the cooling.

However I am not getting any heat to either the main radiator or the heater radiator. The top hose outlet is hot just near the engine, but the radiator is cold and further down the pipe is cold.

I figure it must be either:

1 - Lots of air trapped so no water flow - lots went in, about 6 litres, none dripped out of the bottom(!) I've opened the bleed valve at the top of the system after running and cooling down, and only a small amount went in. Heater valve is open (hot). How can I bleed it better?

2 - Water pump broken - how do I establish if this is the case? Run it with a hose off for a few seconds and see if it flows?

Thermostat blocked - but this wouldn't affect the heater radiator would it?

any suggestions on how to diagnose this and cure it would be greatly appreciated.

Thanks, Mat.
 

melvinmelvin

Member
Messages
264
Location
Bangkok
Actually scratch that - just looked in the garage and I put two whole 5 litre bottles in, so at least 10 litres went in.

Mat.

I have 11 litre + in my cooling system.
Normally I have to fill the system in 3 steps.

Fill radiator, start and run for a while.
repeat
repeat
and then its normally full
.
 

Mat Grant

Member
Messages
143
Location
southern UK
Hi,

No I ran it last night, for about 5 minutes, no heat at heater radiator or main radiator, gauge went up to 80 degrees C (nb the gauge is uncalibrated) engine felt warm on the plenum and the cam covers.

It just occurred to me - my car is on ramps at the front - ie pointing upwards at the front - could this cause air locks round the water pump? When it was first started it had coolant in, and was level.

A few times I've opened the "bleed valve" at the back 9highest point on my car is the hose to the heater, I've fitted a small pipe with a filler cap, to get bubbles out. Each time I've run it, let it cool then refilled, only a tiny amount has gone in here - about 20 ml as a guess.

The outlet pipe at the top front of the engine gets hot, but it is as if no coolant is flowing. I'm going to drain the coolant and take the thermostat out.

But any suggestions on how to confirm the water pump is good would be welcome.

Thanks, Mat.
 

gloverman

Well-Known Member
Messages
3,072
Location
Hamilton. New Zealand
I would run it for longer with a temperature measuring device on it. I have an infrared heat gun. It will be fine up to or just over 100 degrees. Then turn it off and let it sit. Sometimes I do this a couple of times to get tricky ones to bleed.

If you have filled it all the way up on the front factory bleed the waterpump will be full. Pretty rare for the waterpumps to fail but it does happen. I always fit new ones when I do a conversion.

Taking the thermostat out is a bad idea as they are a bypass thermostat so there is a passage left open all the time bypassing the radiator. Was the thermostat new? Does the thermostat go to the bottom of the radiator?
 

cribbj

"Supra" Moderator
Staff member
Messages
4,794
Location
Houston, TX
You could squeeze one of the coolant hoses when the engine is running and you should be able to feel the flow of coolant.
 

Mat Grant

Member
Messages
143
Location
southern UK
Hi all,

Thanks for the replies. Sorry forgot to finish the sentence.... I meant take the thermostat out to test it - wasn't planning on leaving it out. but I've been running it with the heater valve open and the heater fan on, and that is not getting hot.

I've got a Gates cambelt kit with a water pump, bought quite a while ago, but wasn't planning to put it on yet, but in view of the problems I'll put that on now which at least will rule out the water pump.

And i'll double check on the cooling diagram which pipe on the heater loop I've got the bleed cap on - would this matter, or would the air find it's way to the top most point anyway even if it was going through the heater rad first?

I am beginning to realise there is so much I don't know about cooling systems!!! I'll be glad when this is solved and I can actually finish the car and drive it(!) going to see a sprayer tomorrow, looking like booking for September so will have to have the thing sorted by then.

Cheers, Mat.
 

Yotarip

Member
Messages
47
Location
Richmond, VA- USA
My experience. My LS400 started slightly overheating when sitting in traffic and progressively got worse. Eventually the heater stopped blowing cold. I didn't loose any coolant or have any compression issue so I knew it couldn't be the head gasket. I pulled one heater hose while the motor was running and no coolant spilled out. The coolant wasn't flowing. I pulled the water pump and found out the plastic impeller had completely disintegrated. Nothing was left of it. Replaced the pump with a high quality pump with alloy impeller and problem was solved.
 

American Locomotive

New Member
Messages
24
Location
USA
Keep in mind the thermostat really won't open until the coolant hits around 100*C. The radiator in every 1UZ swap I've done stays cold until right about 100*C.
 

Mat Grant

Member
Messages
143
Location
southern UK
Thanks, I've run it for about 10 minutes at a time, just idling and light revs once a bit warm. I've been too scared to let it run longer for fear of causing damage. What is worrying me id that the heat isn't getting to the heater radiator either - shouldn't that be getting hot straight away? The oil is getting hot, I've only got a cheapo infra red gun to measure temps with, and I'm not sure it's that accurate.

it has been getting warm enough to slow the idle down from the 1200/1300 ish fast idle to around 700rpm normal idle (assuming my rev counter is accurate (VDO).
 

Mat Grant

Member
Messages
143
Location
southern UK
hi all, update - I took the radiator hose off the thermostat and there was a lot of air in that hose. So I filled that up and refilled the system, and it started to work.

Since then I have changed the cam belt and fitted a new water pump, got a mate round who is a mechanic to help ensure the belt was timed correctly. The old water pump was intact but had a noisy pulley, so needed changing. I'm doing a couple of wiring finishing jobs while the hoses are off, then I'll be refilling the coolant and will update once it's running again.

Thanks for all the replies and advice on this.

Mat.
 

Mat Grant

Member
Messages
143
Location
southern UK
good news - I've refilled the coolant and the cooling system seems to work. I did a different filling approach, I think last time I got a bubble on the return from the radiator, this time I filed up the return hose from the radiator manually.

I will do a few short runs and after cooling will check and refill, but it's looking good. I left the fans off and let it get hot, it comes back down once I put the fans on, so the system is working properly.

Just a PAS reservoir to go and I can but the aux belt on, put the drivers seat in and do a short test drive. Need to find one that I can fit in my (very shallow) engine bay.

Mat.
 

prackers

New Member
Messages
15
Location
Darlington, UK
I had a similar problem with mine. Before the install I changed the water pump and thermostat but when I ran it the thermostat didn't appear to be opening or the coolant wasn't circulating through the radiator, the fix on mine was to blip the throttle to around 4k which appeared to get everything working. It still does it now if I drain and refill the system until I get it fully bled, then it is fine!
 

melvinmelvin

Member
Messages
264
Location
Bangkok
I got my 1UZ running smoothly couple of days ago.
Experiencing the same cooling problems.

Filled up the radiator to top, about 4 litres.
Started, let it run for a couple of minutes. Opened the radiator, still filled to the top.
Repeat, now maybe running 5 minutes. Radiator? Coolant still up to the top.

Running.
Temp gauge passing 100 degrees. Stopped. Oil and mill is getting heated. Radiator remains cold.
No flow between engine and radiator I'd guess.

Have a temp gauge that is calibrated with the associated sensor.
Dont have a thermostat in the system. (have had too much problems with Toyota thermostats not opening as they should)
Dont have a heater.
Dont have an air conditioner.
Have pressed and pressed and pressed the big water hoses while stopped and while running.
The water pump is Toyota original, new about 3 years ago.
Using Toyota premixed anti freeze, (red juice).
(the front of the engine is higher than the back of the engine, if that matters)

The engine was pretty much drained for coolant before I put the 4 litres on the radiator.
The system has room for another 6+ litres.


What would your advice be re the next steps to try out?
 
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