daxxruckus

Hi all,

I'm a new C4 owner, and have a question. My car has been running hot since I picked it up a few weeks ago (at least according to the temp gauge - hitting 3/4 and then almost all the way pegged). I've already flushed the cooling system, and replaced the thermostat with a new 160dg stat. After doing this, I checked the motor while running with a infrared thermometer and found it wasn't actually as hot as the gauge shows - it was actually hovering around 190-200.

So I wanted to replace the temp sending unit so the gauge would read accurately. In the service manual, and in all the research I've done online, it seems the right temp sender to replace is located on the passenger side of the head, almost back toward the firewall, and it should have a flat blade plug on the end of it. Here is the exact replacement sender that I purchased to replace it:



However, when I checked the sensor that is actually on the car, here is what I found:



It's got a completely different plug on the end, a flat circular end, not a blade plug. Was this replaced at some point or changed from the stock sensor plug? Should I replace it with the new one, and change the connector on the end of the green wire to a blade? Or has something been customized here?

Also, I got a new fan control switch kit (to run the fans at lower temps), and it says to replace the fan switch which is apparently in between the spark plugs for the front two cylinders on the driver side. When I checked on that side, I just found a plug in place, no switch:



Has this been blocked off for some reason too? Is that the correct place to install the temp sensor for the fans in this kit?

https://www.amazon.com/1984-1995-Cor.../dp/B000FL16O8

And finally, this might be a stupid question, but I do I need to have drained the coolant in order to install any of these temp sensors that go into the head/block?

Thanks in advance, I appreciate any help as I begin to figure out how to work on this car!

Here is an album of pics if you all want to see it. It's a 1990 with a Greenwood body kit.

http://imgur.com/a/AZdAu

aklim

What you are looking at is the fan switch, IIRC.

antfarmer2

and do not go by the analog they lie go by your digital.

aklim

I just checked on my 91. Got it confused with the F-body but here it is. Your sensor there is the wrong end for it. What is on the car IS correct as the temp gauge. I grounded it and got some super high temp reading on the gauge. Go get another sensor like the one on the car.

daxxruckus

@Aklim, thank you for checking and confirming. So this rounded plug that is in there right now is the correct temperature sensor for the gauge. I'll return the blade sensor and get a replacement round one.

Can you please check for me on the driver side of yours between 1st and 2nd spark plug and see what you have in the hole where mine just has the flat plug? I'm wondering if another sensor is supposed to be there that was removed on mine.

And can anyone answer my dumb question - do I need to drain the coolant again before replacing these?

Thank you!

aklim

If you cannot, you might have to change the pigrtail. See if GM has one. I did a brief check and you never know but the pictures at the parts stores seem to have the one you have.

I have the same thing. IIRC, since 90 and 91 are similar, you should not have anything there.

You will lose some coolant but you could do it quickly and not lose too much.

WVZR-1

OP - I believe that your connector will work on the newer spade terminal. Both the "button"(on your car now) and the "spade" use a 56 series terminal with the difference being the plastic shell has a slot on one side to allow the slip over on the "button". Check! Your snapshot seems to show the terminal but I don't see the plastic shell.

If it's NOT there a GM# 6288704 will get you what you need to correct that.

Your '90 has 2 fans and neither is controlled directly by a temp switch. You don't need the other part you mentioned and linked to Amazon. Return it if you can or maybe sell here to someone can use it. The plug on the LH cylinder head is OE.

Post the brand and part# of what you purchased for the new temp sender. It can be confirmed.

You don't mention having a FSM but if you do you could check the accuracy of the gauge by supplying know resistance values for confirmation. Simple check to see if it's doing anything at all, disconnected the gauge should go to FULL COLD, ground that GREEN wire and the gauge should go FULL HOT - these checks would be done KEY ON/ENGINE OFF.

This is of course incorrect and I believe you tried to correct.

Increased your post count but you agreed to "misinformation". BTW if the OP doesn't have C68/ATC he has no access to the CTS/ECM temp value without a scanner. Yesterday you were checking "wire connections" on a cable driven tachometer LOL
You could have left it at mentioning the wrong generation BUT no ......

aklim

Look at this on eBay http://www.ebay.com/itm/291839611509

WVZR-1

That's of no value to the OP or anyone else with a C4 - that sender is 1/2-14 NPT, C4 in head temp or fan switch/sender requires 3/8-18 NPT

aklim

Whoops: http://www.ebay.com/itm/Engine-Coola...dWrT2a&vxp=mtr

WVZR-1

GM# 25037346

That's the one I always thought was in the '90 cars, it has unusual GMSPO applications, it's mentioned for all LT5 cars and there's an application for it in a '91 L98. I believe it was also in many of the later LT1 builds. It's been mentioned in many threads. I don't believe it's needed because like I mentioned I believe the connector is the same.

Now NCRS might get involved when it gets more intense and someone will create the NEED FOR this.

WVZR-1

These TEMP ANALOG senders should do all C4's based upon terminal connection type needed:

For the spade/blade GM# 8993146 or 25036135. You could use either of those for a correct equivalent at your local AP store. *** fixed reference part #8993146





For the "button" head GM# 25037346 or an equivalent from the AP store.




For the later 2-pin (I call it "pin & a half") GM# 25037332 or an equivalent from the AP store. It's actually single pin with a "locating pin". The conductor is actually the smaller pin and the larger just for orientation.



I believe that if you have a "button" and buy a spade sender the connector will work, if you have a spade and buy a "button" you'll need a GM # 6288704 to use it. The terminal I believe will release and transfer.



Connector for the later 2-pin (pin & a half), GM # 12126458 or equivalent at the AP store.



I've meant to do this for a very long time and thought "now is the time".

None including the last is meant to be used as a CTS for ECM/PCM or for a FAN CONTROL.

daxxruckus

Thank you all so much. I have the "button head" sensor in there now, and the connector on the green wire is for the same (although I can see it might work on the spade too).

I will go back to Napa and return the blade connector sensor I got and get the button head one instead. Will also do the test by grounding the wire, etc and check the gauge response.

@WVZR-1 - you said "
Your '90 has 2 fans and neither is controlled directly by a temp switch. You don't need the other part you mentioned and linked to Amazon. Return it if you can or maybe sell here to someone can use it. The plug on the LH cylinder head is OE. "

so it seems this fan kit that I got to run the fans at a lower temp won't work with my year. Although they list it for my car specifically. I'll have to call them and see. although if the issue truly is that my temp gauge was just not reading correctly, I don't need this fan kit anyway.

Thank you all so much for your help!

WVZR-1

In this thread there's a set of instructions for using the switch kit that you bought on '90 and later cars and it mentions that the fans are both controlled as I mentioned. Without you having the FSM or a wiring diagram it's difficult to understand but the explanation is quite straight forward.I believe it to be a waste of money, time and materials for '90+ cars. The #2 fan on a '90 is commanded and controlled from the ECM based upon the AC Fan Switch, it could maybe be argued that using the kit/switch could help a '90 or NOT.

https://www.corvetteforum.com/forums...diagram-2.html

I also sent you an email using the CF link in your "userID".

aklim

I really wish you people wouldn't tell us things like that and leave us hanging. Where did you get the button? I would prefer the button since the spade angle would push against my wires.

If the ECM is controlling it, you might not want to change the sensor to this one. Thing is, it would send false readings to the ECM to tell it that it is hotter than it is and thus turn the fans on. That would also change your mixture.

Why do you want to turn it on at a lower temp?

daxxruckus

WVZR-1 - thanks for the email. That link is to the exact instructions that came with the kit. I'm going to hold off on installing it for now though. I bought that kit because my temp gauge was reading extremely high. So I thought if I got the fans kicking on at lower temps, it would keep it cooler.

However, after flushing the coolant and installing new thermostat, and checking temps with an infrared - it seems to not be running that hot (around 200 degrees), which means the temp gauage on the dash is reading wrong.

This led me to want to replace the temp sender that sends reading to the temp gauge. Which led me to find out that the "button head" sender is in place on the car, and in my FSM ( I do have the FSM, someone asked), it shows it should have the blade type. This led me to asking questions on here. I'm going to just get a replacement "button" type sender and replace that. Someone linked me to it on Amazon on this thread. Thank you.

I hope this answers your questions and explains what led me down this path.

WVZR-1

NONE of the senders mentioned in this thread (by me) have anything to do with the ECM/PCM or whatever. They're only for the analog gauge. The exception is the SWITCH KIT that the OP mentions buying and that changes whichever fan to switch temps it's connected to. On a '90 if added to the AUX relay (fan #2) it would be active at the TEMPS of the switch and also the AC switch if wired properly I'd think.

I believe that yours is a '91 maybe?

You might want to take a look at 6E3-C12-1 ... and learn just how each fan is controlled. VSS is part of the ECM calculation so if you've a less than accurate VSS signal - the cooling will suffer OR maybe actually it might be/or will be defaulting to ON at all times.

aklim

I did look at the item you mentioned and the other circuit diagram on the section 8 electrical part of the manual. Last I knew on my 91 Firebird, there was a Hyperjunk sensor that would tell it to come on earlier by simulating a hotter temperature than there was. Yes, you are correct that the ECM will control it. Both of the fans are controlled by the ECM and part of the value is the CTS. I guess what I was wondering is how this would work? Would the new CTS give an incorrect resistance value to the ECM to simulate the "ON" condition? If so, you could be right that the ECM will always turn the fan on.