Temperature Gauge

[Blue90]

I've been closely following all the discussion about operating temperatures. Here's what's going on with my 90 coupe. When I first got it I would get worried when the temp gauge went 2 and 3 bars past twelve oclock.

Four years ago I had GMTuners reprogram the PROM to have the fans come on sooner and I put in a 180F thermostat.

A couple of months ago I noticed a lack of power and poor gas mileage.

Brought it in to a mechanic (who I don't go to anymore) who told me both fans were coming on at 134F and staying on. The fans died while they were diagnosing it. They replaced both fans. They couldn't figure out why the fans were coming on at such a low temp, and staying on.

I went to another shop who confirmed that both fans were coming on at 134F and staying on. They also couldn't determine why.

I went to a pick n pull, got another ECM/PROM, which they put into my car. The fans are now coming on at stock temps. Three bars over mid-way, according to the gauge, is 109C, 226F, when the high fan kicks on.

I got the car back Thursday. Yesterday I purposely went city driving, in traffic, with the AC on, outdoor temp 83F.

I tried getting used to the temp gauge showing 2 an 3 bars over and not being worried about overheating. A half hour of traffic and the gauge spat out another bar, then another, then hit the red and the word HOT came on. As soon as I started to move it went down to 3 bars over and stayed between 2 and 3 bars over for the next hour.

This is why I'm thinking of a new radiator.

But I'd still like to know why my reprogrammed chip isn't working. Ryan, at GMTuners, says the chip can't change unless there's an electrical surge and that would affect the whole ECM.

[padgett]

I would suggest having someone dump the PROM and see what the programming is. The various parameters (fans, TCC) are in fixed places however the exact place varies from year to year.

"As soon as I started to move it went down to 3 bars over " sounds more like an airflow problem than coolant flow. Are you sure the fans are turning on?

If you still have the reprogrammed PROM I'd be glad to take a look at it.

[jonlabree]

The radiator that I have is custom made by a manufacture in the area. It has no plastic and is all aluminum.

[Guest Squire Tom]

un educated questions. i am completely in the dark regarding the ecm and prom.

i do not like to see the temp past the middle in a/c city driving either .

where is the prom located?

is it a part of the ecm ?

how much grief to remove and re program and who does the programming.

are the proms readily available?

again excuse the ignorance regarding this unit.

[padgett]

The PROM is contained inside a CalPak carrier and the combination is known as a MEMCAL. The package is inside the Engine Control Module which is located next to the HVAC programmer above the passenger's right foot.

To reprogram requires a UV eraser (about $60 but will need modification) and a Programmer (about $275 with shipping).

However I have been experiencing an increasing failure rate with factory chips that may be age related. I am looking into replacement with EEProms which would not need the UV eraser.

None is difficult but requires knowlege of programming, the ECM structure, and its contents.

[jonlabree]

Contact Ryan at: Sinister Performance, LLC. for reprograming your chip.

[Blue90]

Sorry I was away for a while. Padgett I'll tell the mechanic, I believe the service managers now called them :otechnicians, what you said when I bring the car back Tuesday.

And if you would PM me or email me, stanleyheld1969@msn.com, about where to send it, I'd be very appreciative if you would take a look at the reprogrammed chip.

Squire Tom,

The ECM is a major pain to remove and re-install. It requires either removing the passenger seat, recommended, or draping yourself over the seat backwards and sticking your head and hand under the dash, disconnecting, pulling, pushing, cursing, and wondering who thought this would be a good idea.

But when you have the shiny little box in your scrapped, bloody and swollen hands, all will be right with the Reatta Gods.

That being said I highly recommend it as a rite of passage for every Reatta owner. It is doable and a highly rewarding and learning experience.

[padgett]

I have never had an issue or needed to remove the passenger seat. Just need to fold the top of the carpet down for clearance. Biggest annoyance is keeping the vaccuum lines out of the way.

[jonlabree]

Well after driving the car some ways with the extra temp gauge, I find that the stock gauge is totatly useless. When reading on the center mark the actual temp ranges from 180' (w/ 180 thermostat) to 210'. So it's not even close to the actual temp. After the center mark on my stock gauge would be beyound the normal, abouve 210'.

[padgett]

That agrees with what I recorded last year. The General wanted it to be straight up for all normal temps. To know what is happening you need to look at ED04.

[Blue90]

Update:

Padgett kindly dumped my reprogrammed PROM and gave me his test results which I forwarded to Ryan Gick. Thank you Padgett, especially your straighforward explanations.

However, even with the stock PROM I still think I'm having fan problems.

The second shop hasn't been a great help. They said they found hydrocarbons in the coolant; they suspect a leaking cylinder head gasket or a cracked head and suggested I replace the engine.:cool:

As Padgett said, ethylene glycol is made up of hydrocarbons. And the car is not showing any other symptoms of head failure: it runs smooth, recently passed emissions test, not using any coolant, oil is clean, oil pressure is good.

Sitting in my carport, both fans come on at 102C/215.6F and both go off at 98C/208.4F. I believe only the LO fan should be controlled by these temps.

So I got out the FSM and listed all the things that could affect fan control, besides the PROM:

Thermostat, water pump, radiator circulation, 3 relays, coolant temp sensor. And then there's always the vehicle speed sensor, the A/C high side temp sensor, the high side temp sensor and even the throttle position sensor.:eek:

Is there a way for me to deteremine the working ability of the coolant temp sensor and the relays? Or is this a job for a shop with testing equipment.

Any other ideas?

Thanks:D,

S.

[padgett]

Keep in mind that there are two fan relays needed 89-91. They operate is series (LO speed) and parallel (HI speed). Both will be turning any time the fan in on, the issue is speed.

(88 is different)

[Blue90]

So is there a way to determine the speed of the fans at any given time;

Such as by using an electrical (volt/wattage) meter?

[padgett]

Probably, the amperage would be significantly less in series than in parallel.

[Guest Mc_Reatta]

There are 3 relays used to control the coolant fans in the underhood relay center.

In 89 - 91 both fans always are supposed to come on together by energizing the pusher and puller fan relay "G" for low speed.

When high speed operation is called for, the second and third relays ("C" and "D") are energized along with the other relay to reroute the power to the pusher fan from the output of the puller fan to full power, and the puller fan output is routed to ground which lets both fans see full power and runs them at full speed.

Easiest way to tell what speed they are turning if you can't tell just by the sound and airflow they give off would be to

go into diagnostics mode and look at ECM Outputs EO09 and EO10.

If EO09 is LOW and EO10 is HIGH, they are in low speed mode. If they are both LOW they are in high speed mode.

Another way to tell is to pull the top off the relay center (need to swing the cross brace out of the way) and pull the relay in position "D"

If the pusher (front) fan stays running, the fans are in low speed. If the pusher fan stops turning, but the puller fan keeps running, then they were in high speed mode.

If you want to confirm the operation of the fans you can go into diagnostics mode and go to ECM Overrides, and go to ES07. Use the up arrow to raise the value to 99 which will turn the fans on low. Then go to ES08 and do the same which will turn on the high speed mode. Use the down arrow to return to value 00 to turn the relays off.

Edited August 15, 2011 by Mc_Reatta (see edit history)

[Blue90]

Thanks for the explanation.

I will go into diagnostics and see what I come up with.

[Blue90]

My trail down diagnostics:

I went to ECM Outputs EO09 and EO10. Where I thought LOW or HIGH might be, under the codes, were rows of short dashes.

When both fans first went on, at 102C/215.6F, I pulled the relay in position D in the relay center. Both fans stayed running, which I'm taking to confirm the fans were in LOW speed mode.

I tried to confirm the operation of the fans by going to ECM Overrides, and going to ES07 and ES08. I couldn't figure out how to hold the code and raise the value. E.g. when I go to ES08 and push the up fan arrow, I get ES09.

[padgett]

Try the temp buttons. 90FSM 8D-7

[Blue90]

Thanks. I'll try it tomorrow, although I'm beginning to believe the fans are not the problem.

[Guest Mc_Reatta]

Yes, use the temp up and down buttons to switch, not the fan buttons.

Your fans were on low which is expected.

Don't think you are having a fan problem.

Did you confirm that your reprogrammed PROM was corrupted causing the fans to come on at 134F?

When was the last time you flushed the cooling system?

Do you still have a lack of power and poor gas mileage?

Did any codes come up when you entered diagnostics?

[Blue90]

Padgett tested the reprogrammed PROM and found it was corrupted causing the fans to come on at 134F. PROM was sent back to Ryan at Sinister Performance for recalibration.

It's been almost two years since the cooling system was flushed.

Power and gas mileage are better with stock PROM.

No codes were set.

[Guest Mc_Reatta]

Would be interesting to find out what managed to corrupt that PROM and how.

You changed out the entire ECM correct? Wonder it was damaged too.

I would treat it as suspect until you can check it out.

So are you experiencing any other problem, or are you just having to get used to the car running back at stock temperatures rather than the lower ones you have been used to?

[padgett]

After examining the contents of the PROM I do not think there is anything wrong there is anything wrong with the ECM or the PROM other than improper FAN 2 (HI) turn on/off.

[Blue90]

I am using my original ECM; only changed out the PROM.

When ther PROM was first changed out I went for a drive in traffic, air temp 80F, and the temp gauge went all the way to illuminating the HOT word. I didn't go into diagnostics to see what the actual temp was.

Ryan thinks it may be a problem with the tuning software he used.

[Blue90]

I received my reprogrammed PROM from Ryan yesterday. Before installing it I decided to check the fan operation.

I went into ECM Overrides: when I got to ES07 and raised the value to 99 both fans came on low; when I went to ES08 and raised the value to 99 the front, pusher, fan went to high speed mode, the rear, puller, fan started to go on , then stopped.

In high speed mode shouldn't both fans be on high?

Does this seem like a ground or maybe a relay problem?

[padgett]

I'd say wiring but they go from serial to parallel then so I'd guess it is the ground side of the puller fan that is missing in HI, in LO the puller grounds through the pusher. TThat might also explain the high engine temp.

[Blue90]

Thanks Padgett,

Both fans are brand new installed by a local shop.

I saw one spiral bound wire group coming from the puller fan and getting lost behind the windshield washer fluid reservoir.

The frame of the fan appears to be plastic. How does it ground?

Where should I look?

[Guest Mc_Reatta]

Don't think you have a problem at all. The override outputs operate the relays separately. ES07 causes relay G to engage which turns both fans on low speed by applying 12 v to the puller fan which is grounded thru a normally closed contact in relay C which connects to the power side of the pusher fan. When you then go to ES08, relays C and D can be engaged. These move the ground path of the puller fan from the pusher fan input and send it directly to ground, and applies 12 v to that pusher fan input causing it to run at high speed. But if relay G is not energized, no voltage is applied to the puller fan, so it won't run.

Only the pusher fan will run, and it will be on high speed.

To get both fans to run in high speed, all three relays must be engaged at the same time. Not sure if this can be done in Override Mode unless the relay can be latched on while the other override is selected and engaged. Not sure if the ECM retains one override setting after that override is left, and another one is selected.

But from what you describe, both overrides are doing what they should, and when the ECM commands all the relays on, both fans will run in high speed.

[padgett]

According to the 90 FSM pg 8D-17, ES07 is supposed to be "puller only" and ES08 "pusher only". I'll try to make time later to check it out.

[Guest Mc_Reatta]

This is yet another example of where the FSM is incorrect.

Part of the problem is due to the carryover of the verbiage from the 88 FSM when the fans were wired differently using a ballast resistor to run the puller fan in low speed mode when relay G was energized, and where relays C and D were used to power the puller fan and pusher fans separately for high speed operation. Relay C was not energized at all during high speed operation.

Unfortunately, the language in even the 88 FSM was not quite correct in that when relay #2 (high speed) as they called it in the override description for ES08, it would not just turn on the pusher fan, it would turn on both fans high speed. Think the tech writer was given some incorrect information on how these circuits were wired, or misunderstood how it operated. There were always three relays used to control the circuit, not two, with one being operated separately, and two operated together by the two (high speed low speed) ECM ground controlling circuits.

I think there was probably a software change from the 88 ECM to the later ECM program so that in 88 the ECM turned off the single low speed relay when high speed was called for and just the two high speed relays were energized whereas in 89 on, the low speed relay has to remain on while the two high speed relays also are energized when the ECM calls for high speed.

Keeping the low speed relay on in an 88 during high speed operation will not cause a problem, but if it is not energized in an 89 during high speed operation, the puller fan won't run just like using ES08 to energize the relays does. In an 88, both fans would run on high speed when ES08 was turned on regardless if ES07 (relay 1) was energized or not.

[padgett]

Simply put, for a 89-91 Reatta, the G relay provides 12v to the puller and the D relay provides 12v to the Pusher. Relay "C" determines if the fans are in series or parallel.

See page 8A-31-1 in the '90 FSM for details. This assumes that the Schematic in the service manual is correct.

All relays are "hot" at all times, switching is through the ground side of the relay coil.

For "LO" only relay "G" is energised through circuit 535. Relay C in NC position routes the ground side of the "puller" to the +12v side of the pusher so both turn at LO speed. (approx 6v on each)

HI speed is accomplished by turning all three relays on and the NO contact of "C" connects the ground side of the puller to ground while "D" connects the hot side of the pusher to +12v. Both turn at HI speed.

Both "C" and "D" are interconnected on the gound side of the coil so cannot be operated independantly.

"G" can be operated independantly however with "C" off it will run in series and with "D" on both will be in HI.

What this means is that since D is always in the same state as C, there is no way to turn the puller (rear) fan on alone.

.................C ........D .........G

None on ........Break. ...Break .....Break

Pusher on HI(2) Make .....Make...... Break

Both on HI .....Make..... Make...... Make

Both on LO (1) Break..... Break..... Make

Now the description on page 8D-16 says for ES07 "coolant fan relay #1, (puller) and for ES08, "coolant fan relay #2, (pusher). I suspect this refers to ckts 535 (output EO9 "relay #1") and 536 (output EO10 relay #2) and the two relays are the outputs from the BCM and not the three under the hood.

This matches the test I just performed on the foundling.

Edited August 25, 2011 by padgett (see edit history)

[Guest Mc_Reatta]

Think it's now obvious that the coolant fan operation doesn't lend itself to being "simply" put.

Your description is for 89 - 91. 88 is different as a ballast resistor is used for low speed operation (only one fan runs) and the fans are never in wired series and relay C is not needed to be engaged for the high speed mode operation like it does in the later years.

I would expect that an examination of the software in the ECM PROM would show a difference 88 to 89 in the control of relay grounding circuits 535 and 536 when high speed fans are called for.

[Guest mounthopewalt]

I remember the good old days when I would upgrade the fan from four to seven blades, and all the cooling issues were resolved.

There is definately something wrong when my Reatta gauge starts to climb from 12 to 2 o'clock when I come to a traffic light.

Is there an aftermarket fan for the Reatta that would draw more air? Or is there a way to wire the existing fan to stay on all the time?

And if the Reatta likes to run hot, maybe it's time to toss out the thermostat for summer driving, as I installed a cooler 180 thermostat, and it made no difference.

[Blue90]

Mc_Reatta and Padgett,

Thank you both for your explanations. I must admit I don't understand everything you're throwing out but I am beginning to understand how this system works. And there is nothing easy about it.

I've even noticed errors in the FSM; it's very frustrating. Thanks for bringing these others to light.

Went driving today for some short-hop errands. Outdoor temp 84F. I ran the A/C and sometimes sat in the sun. I was in diagnostics: When the temp gauge got to three bars over twelve o'clock it read 106C/223F.

At four bars over it read 108C/226F and both fans were on high: I can tell now by the speed and sound.

So it appears my fans are working as the General intended.

If the temp gets to over 108C/226F then there may be another issue.

I'm going to install Ryan's PROM; I'll report back on how the car responds.

[Guest Mc_Reatta]

Stanley, I too don't think there is a problem with your fans.

I have come to the conclusion that the fans running on low speed on a fairly hot day with the AC on are not sufficient to maintain the engine temperature and keep it from climbing up to 226 (at which point the ECM calls for high speed fans) when the engine is hot soaked and the car isn't moving.

At that point they seem to have enough cooling effect on high to keep the temp from going higher. (Assuming no issues with any other cooling system components.)

Installing a lower temp thermostat helps as long as you keep moving, but won't help much when your stopped.

I don't think there are any more efficient fans that can be dropped in place of what we already have.

The best solution I see is to get the fans into high speed mode as soon as possible after the engine reaches your target temp.

This can be done by reprogramming the ECM prom, but this entails the expense of the reprogramming and either procuring a second PROM, or taking the car off the road until the PROM can be sent out, reprogrammed and returned to the ECM.

I have come up with an alternative solution that is less expensive, installs simply and easily in just a few minutes. (plug and play)

It tricks the ECM by causing the fans to run in high speed mode only, regardless if it has called for low or high speed operation.

It does not run the fans if the ECM has not commanded them on, but so far I have not found this to be a problem since whenever the ambient temp is high enough for engine heating to become a concern, I'm running the A/C. And guess what, when the A/C is on, the fans are running.

The hardest part of the design is to get around the monitoring ability and keep from getting a Quad Driver fault.

I about ready to release my design to a few others to broaden the testing beyond my cars.

So far in my first test vehicle with a stock thermostat, I can maintain engine temps between 197 and 201 while running in stop and go traffic below 40 mph. Another benefit is the A/C vent temperature does't climb while stuck at a stoplight, and actually keeps dropping even when stopped if the system hasn't been operating long enough to have stabilized yet.

Long stoplights can raise the temp to 203 which is also what I see on a hot day when running down an interstate at 70 mph A/C on max. (Remember the fans are cut off over 45 mph.) As soon as I exit the highway and resume a steady 40 mph speed the temp quickly drops back to 201 but once hot soaked the temp doesn't drop any lower than that.

While idling stopped for a prolonged period of time, temp climbs to 206 which is the highest temp I have seen in this car since installing.

In another car with a 185 deg thermostat, the car wants to run between 184 and 197 while operating from stopped to 45 mph. I've been fighting both coolant and refrigerant leaks in this car, so I haven't had a long enough trouble free period of testing time under all conditions to lock down what the performance with this thermostat will be.

I feel confident that I have licked the Quad Driver errors, and it won't damage the the ECM, so I'm about ready to advance it from the experimental stage and release it for a broader range of field testing.

[padgett]

Just as a note - so far I have converted two '90s and an 88 to a Stant SuperStat 180F thermostat and reprogrammed the fans to be "all in" by 189F. In 95+ weather they run between 181 and 186 in town with the a/c on max cool.

My experience wih about a dozen 3800s, mostly "C" versions is that given a chance to run cool, they will.

Once the PROM issue is straightened out if you are still overheating, particularly above 50 mph (fans are no needed then), then I'd have to wonder if there is a different problem.

This could range from a clogged radiator (does it feel hot all over when the temp gets above the middle?), defective coolant temperature sensor (is the radiator really hot when it says it is?), or a sticking thermostat even if new (and part of the reason I like the Stant is that it open very fast, have seen thermostats take over 10F from start to open fully).

Try the new PROM and we'll go frm there.

[Blue90]

Yesterday afternoon I replaced the stock PROM with the one Ryan reprogrammed.

The air temp was in the high 80's.

When I started it up, in BCM diagnostics (I wanted to check oil pressure also), the temp read 89C/192F; engine was still warm from my morning ride. I don't think it's worth even mentionning the "gauge" as it was straight up from 89C all the way to 99C/210F.

I drove around the neighborhood, and sometimes sat in the sun with AC on, for about a half hour. The temp climbed, at one point reaching 110C/230F. Moving, less than 40 mph, temp stayed about 105C/221F; waiting at a light it would rise to 107C/225F.

I did not go faster than 40 mph.

It appeared both fans were in high speed mode the whole time.

So the fans seem to be working as directed by the PROM.

Of all the possibilities mentionned (failing water pump?) that could cause the car to run hot where is the best place to start to track this down?

I am running a Stant 180F thermostat; four years old.

[Blue90]

When I opened the hood to check the operation of the fans I didn't know to look for hot spots; it felt hot all over. It was near 100F in the sun.

[padgett]

First thing is to check the radiator to see if the coolant sensor is off. "When I started it up, in BCM diagnostics (I wanted to check oil pressure also), the temp read 89C/192F". If it had been sitting for over 20 minutes I would expect it to have cooled off considerably more.

Can use either an IR temp sensor or just an oven thermometer in the radiator neck.

Next possibility is a sticking thermostat that is not opening properly. If you watch ED04 from a cold start you should see it climb fairly quickly to 82C then suddenly drop five or ten degrees when the thermostat opens, then climb much slower afterwards. That is when the upper radiator hose should suddenly get much warmer.

I do not know what is happening to you but under those circumstances on a 90+F day at a stoplight with the a/c on MAX I can watch the temp come up from about 183 to 189 over a couple of minutes, the HI fans come on and can watch it drop back to 185 where the fans go back to LO. This is on more than one car.

[Ronnie]

Drive down the highway at 60-70 mph for a while to give the coolant temp time to stabilize where it is going to run. Then look to see what the temp is. That way the fans will be out of the picture and you will know if the cooling system is capable of cooling the car down. If it still runs hot the you should investigate the radiator for being clogged. A blown head gasket can also cause the engine to overheat. Highly unlikely the water pump has stopped circulating water but it is possible.

I have a 160* thermostat and at 60-70 mph the engine runs around 174* on a hot day. So the cooling systems are capable of keeping the engine cool if they are functioning properly.

A few years ago I did a modification to my '88 model that turns the fans on at about 190*. I just checked mine this morning to see if it was still performing as expected... and it was. While sitting still in traffic the temp went up to 191*, then the fans came on and cooled the engine down to 176* and the fans kicked off again. The outside temp was 84* at that time. I had the windows down and no AC was on.

Coolant Fan Control Relay Modification*-*ReattaOwner.com

If your fans have been reprogrammed and the cooling system is in good condition there should not be a problem with the engine running cool. I's possible you could have a temp sender giving an erroneous reading to the ECM (and you ) about what the actual engine temp is. Maybe some other means of checking the temp is in order.