bluepeter

Bottom Rad Hose Cold

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Hi, the blue coolant temperature light on our 04 1litre 04 Yaris has started to go out after only a minute or two of driving.

The bottom radiator hose was soft and cold even after driving the car for say 20 minutes. The top hose, the one that has the metal cap above the radiator on one end and the other going to the engine, was nice and warm.

I replaced the thermostat ( with a non OE part from GSF )thinking it was this that had failed and was not letting the warm coolant out of the engine and into the radiator via the bottom hose.

I'm still seeing the same symptoms after this replacement and bleeding the coolant system.

Any ideas what else I can check before I buy a genuine thermostat? Anyone give me tips of bleeding the system?

Thanks, 

Pete

 

 

 

 

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I think you’ve got things the wrong way round.

should’nt warm water go in via the top hose ?

cool, then fall, (hot water falls as it cools)

then enter the engine via the bottom hose

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Water pump impellor slipping perhaps and not pushing the coolant around. Does the heater work well? That would suggest coolant is flowing 

Clogged radiator core.

Perhaps there isn't a cooling issue at all and its a sensor/display problem.

 

 

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so the rad could be blocked?

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Just now, Mooly said:

Water pump impellor slipping perhaps and not pushing the coolant around. Does the heater work well? That would suggest coolant is flowing 

Clogged radiator core.

Perhaps there isn't a cooling issue at all and its a sensor/display problem.

 

 

the heater works fine. I replaced the coolant temp sensor last year. I'm inclined to believe that sensor is still ok because of the heater. That is only my deduction though.

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what's a surefire way of checking for a clogged rad, garden hose into the top and see what the flow is like out of the bottom?

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Hi

That is as good as anything...

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Hi, Put your new or old Thermostat in a pan of water and bring to the boil. If they open then they are working fine, You haven't by any chance installed your Thermostat upside down???

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So i removed the two week old thermostat and put it in some hot water and it opened. I double checked against my Haynes and it was installed the correct way.

I also fitted a new rad. I removed both the top and bottom hose and there weren't any blockages in either hose.

I filled the system back up with fresh red coolant and bled it.

From cold, the blue coolant light on the dash still goes off after less than a mile driving on a 30 mph road and even after a 20 minute drive the bottom rad hose is still cold even when the rad is warm to the touch.

Questions 

1) do you think the blue coolant light should stay on longer than it currently is? I have a new coolant temp sensor to fit. I did fit the current one only last year though.

2) Should the bottom rad hose ever feel warm/hot?

3) If the flow of coolant is out of the engine and down through the rad what function does the thermostat, at the engine end of the bottom hose, perform? It keeps the cool coolant out of the engine until that coolant has warmed up enough to cause the thermostat to open? I thought the coolant would be held within the engine, warmed by engine and only allowed to flow into the rad when it was warm/hot to allow is the cool?

Please enlighten me as I now not sure there actually is an issue with the car, it may be my understanding that needs fixing.

 

 

 

 

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Two important questions:

1. Did you switch the heating to fully hot when draining and refilling.

2. Did you bleed the system of air after refilling.

 

If the answer to both is no, you have an airlock. Bleed the system of air.. https://tinyurl.com/yayqrawn

 

 

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22 minutes ago, Madasafish said:

Two important questions:

1. Did you switch the heating to fully hot when draining and refilling.

2. Did you bleed the system of air after refilling.

 

If the answer to both is no, you have an airlock. Bleed the system of air.. https://tinyurl.com/yayqrawn

Yep, I did both. i'll take a look at that link though, thanks. 

 

 

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 Coolant flows through the engine and heater until it gets hot enough, then the thermostat opens and sends the hot water to the radiator.  The rad cools it and cold water returns to the sytem.

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One thing I never really appreciated until a dealership service manager pointed it out was that thermostats don't really 'open' like they do with the boiling water test and dangling one in it. Rather in operation the valve 'hovers' on its seat with mostly a minimal amount of space. The boiling water test can therefore be a little misleading and even a faulty stat can open under such brute force conditions

I would think in this cooler weather that the bottom hose will never get anything more than lukewarm if at all. Surely someone with a similar age Yaris could tell you how long this light takes to go out.

 

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Bit late replying but......

Your "problem" I suspect isn't a problem at all.

The bottom hose on a car (in winter or cool weather) never gets hot until

the engine is fully up to temperature and then allowed to sit stationary with the engine running and heater off, so thereis no air passing over the radiator. 

The thermostat usually has a tiny bypass hole to allow the passage of a miniscule amount of water all the time so that the thermostat is ready to open as soon as necessary.
In the current climate, even at walking pace, the very efficient aluminium radiator will instantly cool any water passing through it.

Probably the only way to test it is a swift run up the motorway. Leave the engine running with heater off, the radiator will quickly get hot from top (first) to bottom.

By the time the bottom hose is hot, the radiator fan will cut in and ensure water returning to the engine is cooled.

In winter (now) our blue light takes about a mile to go out.
in summer, about half that.

I think your car is perfectly normal.

Ian.

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22 hours ago, Unklian said:

In winter (now) our blue light takes about a mile to go out.

At 43degC. I've checked!

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