FireInMe17

Does anyone have any idea why the coolant temp sensor on the intake isn't getting any power? Car is getting really hot and the fans won't kick on. Car is a 1990 355 TPI. Not sure why the fan isn't coming on...

sofakingdom

iTrader: (1)

Power?

The coolant temp sensor is a variable resistor. The ECM measures it, and its resistance tells it what the temp is. It doesn't get "power" like, say, a TPS, does. (which is a 3-terminal variable resistor that forms a voltage divider: at any given throttle position, its output is some fraction of the more-or-less constant "power" voltage) I think you don't understand electronic things completely. Which is not uncommon, or to call you "stupid", or any such thing; but that doesn't mean the things in your car are supposed to work some other way than they actually do, just because you don't understand them.

Let's start at the beginning, which you seem to have skipped over a number of steps. What makes you think (a) the car is "really hot", and (b) the fan is supposed to "kick on" whenever you are thinking it should, whenever that happens to be?

FireInMe17

I just got done swapping in my 355 TPI to my V6 car, installed the dual fan set up, started the car for the first time and the fans did not come on. Car got warmed up to 230 and we shut it off. I got Scott Hansen to burn me a custom memcal, and he set the fans to come on at 195 and shut off at 185, car has a 180 thermostat. I know the fan temp sensor runs the secondary fan, but the CTS tells the computer how hot the engine is even to turn on the primary fan and engage the fan relay. The relay is new so that's not the issue. I don't know what it could be. So no, I'm not stupid, just figured the sensor had some sort of power supply.

sofakingdom

iTrader: (1)

Factory setting for the fan switch is around 235°.

In other words, the factory guys (not that they know ANYTHING AT ALL about the cars they designed, but w/e) didn't think the motor even would BEGIN needing cooling until it reached 235°.

So no, if you saw 230°, your car was PERFECTLY FINE, and the fan shouldn't have come on yet.

When you looked at the data "stream" (trickle, dribble, drip, occasional droplet...) coming out of your ECM, what did it say it thought the engine temp was?

FireInMe17

I've had the car warmed up hotter than that and the fans are not working. Tested the fans with another power source and they do work but the car will not turn them on.

FireInMe17

Anyone have any ideas what to start checking?

sofakingdom

iTrader: (1)

What is the engine's ACTUAL TEMP, measured with an external instrument?

What does the ECM report that it THINKS the temp is?

What happened when you swapped out the coolant temp sensor?

tom3

How about the secondary fan control in the passenger side head? Does this year/model have this. That's a fail safe that should turn on the fans at about 240 degrees. Good mod might be to change this sensor to a lower temp and let it override the ECM control of the fans.

ploegi

Either that, or just ground it out, and see if the fans run..... that would assure at least THAT part of the circuit.

You should be getting like volts volts on one pin of the CTS. If you aren't, you have a wiring issue.

FireInMe17

Still messing with it, I have voltage to the CTS now, and the fan relays have +12 volts but now I can't figure out why the relay isn't turning them on. When I jumper the wires manually, the fans will work, but theres no automatic control by the computer or anything...

sofakingdom

iTrader: (1)

Are you EVER going to measure the ACTUAL ENGINE TEMPERATURE with an ACTUAL MEASURING INSTRUMENT, and compare it to what the ECM says it THINKS the temp is?

Have you simply swapped out the $5 coolant temp sensor and see if your problem got fixed in exchange for $5 and about 5 minutes of your time? (or probably less... I could do one in 5 minutes, but I'm really slow, so you could prolly do it in half the time or less...)

Posting on the Internet over and over again doesn't do A DAMN BIT of good unless you at least attempt to act on the "advice" you get. Gotta GET YER BUTT UP OFF THE KEYBOARD AND ACTUALLY DO STUFF once in awhile.

John in RI

iTrader: (167)

That's true,......BUT ( Isn't there ALWAYS a BUT ! ); that is the rating for the fan switch in the head / secondary fan. Do you know what the primary fan /CTS temp is set @ ??


:driving :

FireInMe17

Why would I go so far as to check to see what the computer thinks down to the decimal the temperate is? Do you think I'm that stupid not to know when the gauge says its over 210 and oh my gosh the engine is really hot, I probably shouldn't touch it again, and nothings coming on to cool it that something isn't right? Not no, maybe just beacuse the gauge is buried in the red, maybe I should give it another 5 minutes until I start to see steam if its really hot or not???...


I just put this whole car together, do you think I would cheap out on somehow bad sensors for it? Everythings brand new, annndddd I did swap it out with one from a different parts store just to be sure...and still no change.

someone972

iTrader: (2)

If you've verified that the fan comes on when jumped (which it sounds like you have), and it sounds like the CTS is OK, then the next step in figuring out why the computer isn't signaling the fan to turn on is to see what the computer is seeing. Just because the sensor/memcal is good doesn't mean that the wiring is not damaged somewhere, or that the ECM does not have some electrical fault. Knowing what the computer is seeing will help to narrow down what to look at next. Do you have access to a cable to read the OBD1 information?

sofakingdom

iTrader: (1)

Because if the ECM thinks the engine temp is 150° or something instead of whatever it REALLY is, it will NEVER turn on the fans. ASK IT what it thinks, don't ASSUME that just because some stuff is "new", that everything is perfect.

The gauge reading is not connected in any manner way shape form or fashion with the ECM's point of view.

Gauges are NOTORIOUS for being inaccurate, for any number of reasons besides ... inaccuracy. For example, an unsuitable choice of sending unit location, or a wiring problem. Which is why, NO MATTER WHAT, you need to MEASURE THE ACTUAL ENGINE TEMP with an ACTUAL MEASURING INSTRUMENT. Even a Harbor Freight Red Army cheeeeeeeepie.

Until you know WHAT THE REAL ENGINE TEMP IS, and can compare it to WHAT THE ECM THINKS IT IS, you will NEVER be able to figure out why the resultant behavior fails to meet expectations.

Not sure why it's so hard to get this point across.

John in RI

iTrader: (167)

Temp gauges are notorious for being wildly inaccurate and should never be trusted until verified. My "problem" with off the shelf temp lasers is that I trust them to be accurate as much as I trust a factory temp gauge.

To be perfectly honest ....> that's EXACTLY how I usually determine if there is a temp/fan problem on some cars. (always check for proper coolant level and mix as well as a properly rated PSI cap ! ) Not to say it's the right way - but I don't need any "tool" to see/feel what's happening. First; I TRUST that when the radiator hose gets hot, the thermostat has opened up, there's no mistaking when this happens. (check stock gauge and compare to thermostat rating) and then I TRUST that once the radiator cap opens and the overflow tank starts filling up with boiling coolant, it's beginning to overheat. Again; there's no mistaking this. (should boil right after temp gauge climbs past 240.) If the Thermostat opens and the gauge reading doesn't match - AND/OR - If the gauge reads 240+ and the coolant isn't boiling, the gauges LIES ! Since I'm specifically checking for an over-heat,..... AS SOON AS the radiator cap opens I shut it off, no harm done. ( If a head gasket blows in this instance it was already junk and I did myself a favor ).


And for the record; The Temp Gauge in my Berlinetta was always right 'on the $$'. For years I ran with a HP 355ci carb that would get real-hot,... real fast when beating on it and I would watch it swing from cold-cool to red-hot and back again. A few years ago I converted to an LT1 & ever since my gauge reads lower than actual temps. I have replaced the sensor several times, swapped gauges a couple times, and even plugged in other clusters to be sure it wasn't the printed circuit, everything ALWAYS checks out OK. I can see what the ECM coolant sensor is reading on the laptop and my thermostat and fans work at the right temps according to the PCM...... but STILL, my Temp Gauge consistently reads lower than it "should" after the LT1 swap.

John in RI

iTrader: (167)

I had to re-visit this due to recent events !

Got a car back that I sold a couple years ago. As I was going thru the checklist of the things I want to be sure are OK before I re-sell the car I wanted to check the cooling system operation. Started the car and let it run until it got to about 200 when the thermostat opened up and the upper hose got hot. At 240 degrees ( middle of 220 and 260 ) still no fan,...... another minute or 2 goes by and the Radiator cap ( 16 lbs: pretty sure stock is 15 lbs ) starts to release hot coolant back into the over-flow as the needle touches the RED, and still no fan. Shut off the car and grounded the fan coolant sensor,... fan kicks on.

Now I know the thermostat is opening when it should, the gauge is accurate, The Fan Relay is fine ( checked AC override as well ), and that the fan sensor is the problem,............ NO HARM DONE !!

I've got to ask how you made out with this FireInMe17 ?? The checks I described above will only apply to your secondary fan but it's a perfectly good test to run to be sure that at least the secondary system is OK.


DOES ANYONE KNOW what temp the STOCK Primary fan should kick on @ ?? ( CTS rating for ECM fan control ? )

John in RI

iTrader: (167)

Well, I was wrong again !!


This car had 2 Fan Switches already installed; 1 was mounted in the aluminum intake and the other was mounted in the thermostat housing. Both switches appeared to be stock units and even though the engine temp ( by gauge and overflow activation ) showed temps of 250+, as soon as ground is applied to the switch's wire ( or the HVAC controller is turned to AC ) the fan activates.

Pretty sure I put the sensor in the Intake because the head mounting hole plug was stripped. I also remember that the fan was working when I built this engine a few years back. Seems like it failed at some point and the guy I sold the car to installed another switch; and now neither one of them works.

I removed both of the sensors and installed a plug in 1 hole and a BRAND NEW STANDARD MOTOR PRODUCTS Part # TS136 ( ON @ 212 degrees & OFF @ 204 degrees: ) in the intake hole and again,..... the fan did not activate. While the engine was still @ about 250 I jumped a test light from power to the switch,... and still no ground. I find it hard to believe that the new sensor was DOA,... I guess it's possible. I'll have to leave it alone for awhile and maybe buy another (stock) sensor to give it one more try.

I know that the stock location for this sensor is in the Iron head and not the aluminum intake or stock water neck, but I'm not ready to remove the pass side header to access that stock mounting spot - not yet anyway !!

Didn't mean to step on your threads here, but I wrote about this problem, then had a very similar problem,... and what seems like a simple problem is not a simple problem !! I'm guessing it's due to the heat transfer to the switch, (Iron vs. Aluminum) AND location of sensor ( top of system rather than next to a combustion chamber. )