Coolant temperature question

[Takeshi]

Hello

I am struggling with the subject problem occurred on my Seven ('98 1.8 K-series VVC with heater)). I knew there were many threads on this topic. I read through most of them, then followed the instructions there, but still I can not solve it.

 

Sympton: Few minutes after starting the engine, coolant temperature gage goes up to max. position (120 deg C). Just like similar quiries, lower coolant hose and radiator is still cold at that moment. Engine, hose from engine to heater, hose from heater to radiator became hot.

 

After I bought the car in Jan 07, I did not touch cooling system. It worked normally until early March. But I still doubted the possiblity of air lock, since I thought the gage should go up immediately after turning on the system, if the temprature sender is dead.

 

I jacked up the front and tried to bleed at the plug on the top of radiator, but my jack could not raise radiator plug higher than the heater hose.

 

Then tried to bleed at heater hose connection where it is the highest point in the system. I felt some amount of air came out there and then water came out. Therefore I felt I could bleed the system. But the sympton still did not disappear.

 

Now I have got the following questions...

* Should I now judge the temperature sender is failed?

* Are there still some possiblity of air lock?

 

Thank you for your advise in advance.

 

 

[Myles]

A new temp-sender costs around a tenner delivered (or did last time I bought one - before giving up as they kept on failing) and is easy to fit - as long as you remember that it's a tapered-thread and shouldn't be over-tightened.

 

It's as well to change it (I'd buy two so you've got a spare for when this one - inevitably - fails). You can then start to chase down problems with one more variable removed from the equation...

 

          🙆🏻 🙆🏻 🙆🏻 🙆🏻 🙆🏻

Alcester Racing

7s Equipe™

^🙆🏻 🙆🏻 _🙆🏻 🙆🏻 ^🙆🏻

 

Alcester-Racing-Sevens.com

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[Takeshi]

Thanks, Myles.

I now feel your adive would be practical. I think I will go that way.

[Takeshi]

I got a new coolant temperature sender and installed it.

But the situation was the same....

What I noticed was,

When I took out the sender, coolant did not come out at all....!?

 

I will go to a garage, ask them to lift the front up and try to bleed again.

[willitgo]

I had lots of problems at one stage with this kind of issue - and they started for no apparent reason.

 

In the end I bled the system with the engine running, opening the bleed screw on the radiator (posted details a while ago) - I don't believe it is necessary to jack the front of the car,this seems to be in order to cause any trapped air to rise to the highest part of the system. However, you can still have air trapped in the header tank of the radiator which is what usually causes the problem.

 

Hope you get it fixed.

 

Colin

[Takeshi]

The garage I went today was too busy to play with me... (No, I should have made an appointment for the work..)

Colin, thanks. I will put your suggestion in the next action list. It is relatively easy..

 

 

[Myles]

When I took out the sender, coolant did not come out at all....!?

 

Well, on my k-series, the water-rail pretty-much is one of the highest point in the system (there are a number of slightly different designs, so YMMV) - and if the system is cold, it won't be under pressure.

 

          🙆🏻 🙆🏻 🙆🏻 🙆🏻 🙆🏻

Alcester Racing

7s Equipe™

^🙆🏻 🙆🏻 _🙆🏻 🙆🏻 ^🙆🏻

 

Alcester-Racing-Sevens.com

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[Takeshi]

On my case, the water tube is not at the highest position. Radiator header and heater unit are obviously higher than it... So I wondered it. Thanks for the reply anyway.

 

Today I did a test to check if wiring and gage are working correctly. (I still could not believe the coolant in the system could go up to 120 deg C so quickly. I could not find anything wrong with the running engine, except gage reading.)

 

Test procedure:

- Connect the wire for coolant temp sender with the spare sender. (it is the one originally installed. Assuming it was live, since the new sender did not change the situation, as I mentioned before)

- Tie one another wire around the thread of the sender, connect the other end with negative terminal of the battery.

- Dip the spare sender into hot water in a mug cup.

- Turn on the iginition switch of the car and check the reading of the gage.

 

Result:

- When the water in mug cup was very hot (Assuming it was between 90 to 95 degC, since it was just after pouring from boiling kettle), the gage indicated almost around 120 degC (just edge of "rad zone".)

- A few minuites later, the water in mug cup became cooler, as I could dip my finger in it without having too much pain. (Assuming around 45 to 50 deg C). The gage still indicated around 80 deg C.

 

Now I've got some confidence that the gage reading is much higher than acutal. I know I can't dip my finger into 80 deg C water.

 

Next question is...

gage?, wiring?, even the new sender is dead?

(But, I will still leave the possibility of air lock and sticky theromostat.)

 

Question:

Is there anyone who knows cooling system schematic in K-series engines?

I drew it with my understanding, but I would like to confirm if it is correct.

I thought knowing it would help solving the problem..

[Takeshi]

Now I have solved the problem. It was due to faulty gauge. (Open circuit in the gauge)

I replaced it with new one (Part number 71229, failed one was 71164R.).

The new gauge indicated around 80 to 90 deg C. Thanks for all of your ideas.

 

If some one faces the smilar situation, I would recommend to check resistance between each terminals, before ordering replacement parts.

 

For your information

New gauge (good one)

12V input vs. sender input: 0.3 kohm

12V input vs. grand: 0.5 kohm

Sender input vs. grand: 0.2 kohm

 

Failed one

12V input vs. sender input: 0.3 kohm

12V input vs. grand: open circuit

Sender input vs. grand: open circuit