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Overheating troubles
Not too shy to talk
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Can anyone tell me... if you measure the voltage from the temperature sender wire to ground, do you read a steady voltage with key ON?
I get 10v for 5-10 seconds after turning key to ON, and then it will rapidly change between 10 and 2-3v. Is this normal? The internal regulator regulating? Should it be 11-12v? I need to rule out my temperature gauge/sender as I have replaced everything except water pump which is on its way.

If you care, some more info:
I have recently installed a blow through turbo that is plumbed in parallel to the heater core (teed off at heater outlet, teed into heater return line).
Before turbo car used to idle slightly above half way (although it has seemed to progressively become warmer over the years. A timing bump at one stage helped it drop a little). Now it is reading 3/4 or more and rises quickly to H line when driving/cruising off boost. Radiator is a brand new aluminium 3 row. Replaced thermostat with new 82 Celsius fail-safe (old one was fine though). Block has been water flushed.

Running 6-7 PSI and have timing set at 10 initial + 15 mechanical by ~3k RPM + ~15 manifold vacuum adv. When I first installed the turbo I had 5 initial + 15 mechanical and no vacuum and it seemed to run cooler and didn't get to the H. One short drive it did, popped the cap with it running still and didn't see any flow. Heater hoses felt empty, think that time it was an air lock as I checked after idling the next day and it was flowing again. After that I added the vacuum advance giving 26 degrees advance at idle and made no difference to when it was running 5-10, if anything it seems to run warmer.
I Am still in the process of tuning but AFR mixtures are relatively good already but haven't been brave enough to drive it far with it running so warm.

Problem seems to be getting worse gradually so I now suspect water pump. Removed it today and its pretty lumpy but still in one piece and spinning. The last few checks of the flow across the radiator seemed slow though. Have a replacement on the way.
I am hoping that will fix it.
Otherwise I am thinking maybe lower radiator hose is sucking closed a bit. Or I have failed with the set up and it is just circulating hot coolant through the turbo over and over and reducing the flow through the radiator? Maybe blown a HG already?
Does your turbo engine run warmer than it did stock (just cruising, idle etc.)?

Posted on: 3/11 9:25
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Re: Overheating troubles
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voltage like that is normal. The gauge has varying voltage

The sensor works with resistance, so measure that:
*100 Ohms @ 50C (122F)
* 20 ohms at 180F (normal engine temp)

Posted on: 3/11 10:14
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Re: Overheating troubles
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Thanks for the clarification dd.

Pulled the sensor and heated in a pot of water. Getting readings of 130 ohm at 50c and 50 ohm at 82c. Wouldn't higher resistance readings would cause the gauge to read lower not higher?
Will replace for peace of mind but now I think I am more confused.

Posted on: 3/12 4:15
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Re: Overheating troubles
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Get silicone hoses off eBay to rule out hose collapse and try to run a larger radiator with fan shroud if able.

Posted on: 3/13 14:51
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Re: Overheating troubles
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You can test the flow without any special tools -- observing flow under the cap doesn't tell much. But since you are buying a new radiator, just wait and see if that fixes it. It usually is the cause of overheating ... another common cause is electric fans not cooling it enough

with turbo idling or cruising it won't shouldn't run any hotter than stock. Only more cooling is needed when making more power than stock

Posted on: 3/14 4:47
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Re: Overheating troubles
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Thanks for your input guys.
Just to clarify: I have had a larger shiny radiator for a long time, onto my 3rd $150 eBay one. Used to sit on 1/2 way line all day and maybe creep up a little on warmer days. At some stage (can't remember when or why, maybe slowly over time) it began to run at over 1/2 way line and I think it has progressively gotten worse. Makes me think water pump or sensor/gauge.
Have the eBay silicon lower hose
New water pump on its way
New sensor on its way. Pump will go in this weekend, may test with old sensor if new one hasn't arrived.

Testing temp gauge with 20ohm and 100ohm resistors tonight to verify the gauge is accurate. Will report back with results!

Posted on: 3/14 6:08
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Re: Overheating troubles
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Go to Harbour Freight and buy a $15 temp laser. Measure the temp of the cylinder head by the spark plugs. It should be very close to the thermostat rating. If the sensor or gauge is way off, then you'll know. You can test the laser by measuring temp inside the house and on various other engines

Posted on: 3/14 8:02
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Re: Overheating troubles
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Tested the gauge with a resistor between the sensor wire and ground.
20 ohm:
Open in new window


and with 100 ohm:
Open in new window


At least it was only pretending to overheat I guess.

Not sure where to go from here. Is there a way to calibrate or change the gauge?

What is the "too hot" range for engine? 95c?

I have got a temp gun DD, and did check head temp at one point, but wasn't sure what I should expect to see/how accurate it was reading on the metal. It's been pretty handy to have, good suggestion!

Posted on: 3/14 8:57
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Re: Overheating troubles
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Good pics. With 20 ohm it's supposed to read 1/2 way. With 100 ohms, I believe it should be on the first line, so that looks good

It seems to me it's a gauge problem. Yes, the gauge can be calibrated by adjusting the regulator. This will also affect the fuel gauge. There is a screw on the regulator, not sure how to adjust it. The voltage swings back and forth, maybe adjust the voltage a little bit one way or another, or maybe increase/decrease the points gap a bit

Or maybe just file the points a bit. Might be a tiny bit corroded

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Posted on: 3/14 9:15
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