Eng Temp Problem - HELP!

I've got a problem and I KNOW someone out there can help.<P>Essentially, I've got a 1990 Reatta where, per the engine temperature gage, easily shows an overheat condition. HOWEVER, after having the radiator rodded out, the coolant replaced, and the water pump replaced, no improvement. But, I'm told, that when the shop measures the temperature themselves it's fine.<P>Fortunately/Unfortunately, there appears to be a fail-safe command in the system. Specifically, whenever the gage shows past center midpoint (normal) and I turn the car off, it won't restart until the motor compartment cools enough to return the gage to the midpoint or less. For me this means that when I drive this car, and it's sort of warm outside (80'F or better), if I stop to go in a store I put my hood up before going in!<P>I've scheduled this car into a garage for another look-see - any suggestions?<P>Thanks,<BR>Rita

My '90 coupe tends to be the same as yours. The Buick garage tech checked the temperatures and found them to be normal. You could install a 180 degree thermostat especially if you live in a hot climate.

Had same problem with my '90 coupe. Tried to diagnose it myself from posts on the forum. Was convinced it was fuel pump relay. Replaced, problem not solved. Then thought it was probably the fuel pump itself. Took it to a dealer. They found two bad injectors and replaced them, along with the 180 thermostat I requested. Assured me that the car was fixed. Went to pick it up and it would not start. Final diagnosis was crank sensor. Since they replaced the sensor, I start first time, everytime, even when warm. I will say that everytime the dealer suggested a solution, I logged on to the forum to verify that it was a possible cause of the problem. Hope this helps.<P>BTW..the 180 degree thermostat solved my high temperature reading. Gauge never gets above the 12 o'clock position.<p>[ 07-18-2002: Message edited by: hicamper ]

I would question whether to change to a 180 degree thermostat. I thought a 180 was a good idea in my '92 S-10 Blazer. But a mechanic that I really trust and respect suggested otherwise.<p>At least in the case of my S-10, he said the computer will allow a richer fuel mixture until it senses the engine is warmed up to normal operating temperature. So by using a lower temp. thermostat, the computer never thinks its warmed up yet. Thus it will continually run rich, giving lower MPG.<p>So when I recently needed a new radiator put in, we switched it back to the proper 195. And presto, I'm seeing a slight improvement in gas milage.<p>Does anyone know whether this would be true for the Reatta too?

From my understanding, the Economy Zone with the Reatta and easily confirmed on the '88-'89 thru the CRT, is when the ECM kicks into Closed Loop. This should be where the ECM leans out the Fuel delivery to optomize economy.

Rita,<P>I can certainly sympathize with your plight. I too have spent many hours trying to ascertain the 'fault' in my vehicle.<P>For nearly three years, in hot Hawaii weather (for what that's worth , the temp guage would never ever get about 12 oclock.<P>One day at the car wash, the gauge slipped to 1, then 2PM. 4 months later, and the below check/replacements, no change. Although I have yet to tear-into the car, I still suspect that its either a weak water pump (not likely), or a small restriction in one of the coolant passages. Of course, to check that, would require a major tear-down of the engine.<P>My diagnosis? Turn up the radio. If you're really really worried about this, install a 180F Stant thermo. I did this, but returned to the 'factory' 195F for emissions and MPG's.<P>--Tom<P>(exerpt dated 17 June 2001)<P>Background:<P>1990 Buick Reatta, 3800 engine, bought in 1977 with 33K, presently 74K. Routinely flushed and changed the coolant with Prestone every year. Both puller and pusher fans operate all the time on AC (which is on all the time), and ECM/BCM combination is programmed to enable high- speed fans at 115C. Both fans are normally serially connected at 12V, then through the fan relay, are switched to parallel when temp exceeds 115C.<P>Over these last three years, my analog temperature gauge has quickly warmed up and has always pointed straight up at 12 oclock (9 bars, with 4 on the left, one straight up, and 4 on the right). The temp gauge has ALWAYS exhibited this straightup condition during times of cooler as well as hotter weather, either on the highway or in town.<P>I watch the instrument panel all the time.<P>Details:<P>Since 4 weeks ago, while at a stop light downtown after running for 45 minutes, the temp gauge climbed to 1, then, 2 oclock. Essentially a different temperature and I at first thought it was a temperature blockage inside the engine block.<P>I changed the existing thermostat (which I assumed was an OEM 90C/195F but cannot now confirm that) with an after market NAPA unit, but no change. Upon starting up in the morning to go to work, it quickly rises up to normal 12 oclock position, and stays there until 30 minutes later when I pull into the parking lot. However, in the afternoon, when the outside temperature is higher, upon arriving back home from both highway and city driving, the gauge reads 1 bar to the right at 1 oclock, then, 2 etc.<P>Entering in the on-board computer readout (ED04), the temp bounced from 88-93 or so during the first 30 minutes, then, in the afternoon going back home, the temp would rise to 95, 100, 105 and then, 109. Fans have not gone to high speed mode, since the temp didn't exceed 115.<P>This is/was a change in the normal operation for this particular car.<P>Brought into the dealer, and they:<P> R/R Radiator cap<BR> R/R coolant sensor<BR> R/R Thermostat (unsure brand)<BR> Checked/swapped the ECM and BCM computers<BR> Indicated to me that the Instrument Panel Cluster was bad (reading too high) <P>I bought a used IPC from PA and had them send it to me. I installed the IPC and it ready the exact same reading on the replacement.<P>Wanting to prove the coolant sensor/ECM/BCM/IPC combo were good, I went to Radio Shack and bought a 5K ohm potentiometer. Warming up the car, I removed the plug on the coolant sensor, and took several measurements, substituting the potentiometer for the coolant sensor. Readings confirmed factory settings and values:<P>DigitalTemp Ohms<BR> 85C 261<BR> 90C 233<BR> 95C 197<BR> 100C 168<BR> 105C 164<BR> 110C 126<P>Bar 'switch on analog gauge':<BR> 83C 12 oclock<BR> 99C 1 bar (1PM)<BR> 102C 2 bars (2PM)<BR> 105C 3 bars (3PM)<BR> 109C 4 bars (4PM) <P>It does appear that the coolant sensor to the IPC is good.<P>Thinking that the radiator was bad, or blocked, I then took it to a radiator shop for R/R (dealer wanted >$700, shop was $242. The original aluminum core radiator was not plugged, but it did have some cracks in the plastic tanks on the side. Good preventive maintenance I assume, but did not change the situation, so I looked at Stant's Premium non-linear thermostats. Armed with a premium 90C unit, the car quickly warms up to 95, then again, slowly climbed to 105 or so. Thinking that I still have a blockage problem, and desired to keep it near the 90C factory temp, I changed out the Stant 90C with a Stant 82C unit.<P>Now, the unit warms to 83-88 or so, and in the wam afternoon, rises to 109 in town without moving. Getting back on the highway, the temperature gradually lowers to ~88-93C.<P>The question remains - why is the temperature differential STILL 15C in warm weather?<P>If Buick designed the car this way (to rise slowly) why did my car exhibit solid temp readings?<P>Do all cars warm to 110C in warm weather?<P>--Tom

Living in warm climates I have found that the cooler you run an engine (within limits) the longer things last. I use 160F thermostats in non-computer cars and 180F (82C) in computer cars like the Reatta.<P>The Reatta IMNSHO is somewhat undercooled - the radiator is 10% smaller in surface area than in my Bonneville with the same engine. The odd part is that it is not shorter bur rather is not as wide.<P>Secondly airflow is critical - with the <a href="http://www2.gdi.net/~padgett/enk1.jpg"><span style="font-weight: bold">bra installed</span></a>, if I do not open the license plate flap, it runs noticably hotter. Further, once it gets hot (and by that I mean 200F), it is hard to cool back down while driving.<P>Consequently I also reprogrammed the PROM to turn the fans on earlier - LO speed at 185F and HI at 190F. Once this was done it usually sites in the 183-188 area on a hot day and sometimes I see a peak to 192 at stoplights when leave the interstate that comes back down quickly.<P>In the couse of this I have analyzed most of the other PROM settings as well and for the "C" engine, once it reaches "closed loop" operation (basically when the coolant reaches 146F) only three variables have any change as a function of temperature: Power Enrichement, EGR, and Accel Enrichment. Further none of these change between 176F (80C) and 260F (128C).<P>So with a 180F thermostat the ECM will command the same values as a 195F once warmed up. (Cannot speak to other engines, YMMV).<P>It is possible that a slight MPG increase may be seen at higher temperatures but is due to charge dilution and less oil drag rather than ECM commands. Personally am willing to trade a minor MPG loss for the longetivity inherant in cooler underhood temperatures for things like electronics, hoses, belts, and batteries.<P>ps any gain will be wiped out immediately if OldPA3 counts start climbing due to higher operating temperatures.

Tom Jenkins is probably the foremost authority on this subject re. a 1990!<BR> I had 2 , 1989's (readout on CRT, no gage as in 90, 91) and now have a 91(same as 90 gage)<BR> My guesstimates:<BR> 12 O'clock is about 195*<BR> In the Red is something over 227*, probably more than 230*. If it does not reach Red it probably hasn't really overheated!<BR> Normal readings in hot wx., going less than 40mph, are 203/208/213, more guesstimates but what both my 89's indicated in numbers.<BR> My 91 has seen 3 O'clock( suspect this is about 213*), in slow traffic, after fast run then stopping/idle. Always recovers quickly, even idling.<BR> Suggest you confirm correct fan functions and switch to 180* thermostat. ( I switched both 89's, not yet in 91) Switching made a considerable difference.

Wow! Great feedback so far. Your comments reminded me that I have also replaced the one fan as well as the instrument panel (obviously, didn't solve problem).<P>However, it certainly sounds like trying out a 180' thermostat is a good shot. I drop the car off tomorrow, Saturday, and they'll start work Monday. Will let you all know how this turns out.<P>Again, Thanks!

Padgett, I have a 91 Coupe and the correct service manual. How can I re-program the fans. You can e-mail me at dhbarrette@prodigy.net.<P>Thanks in advance.

In most cases the high temp reading is either a defective sending unit or a thermostat.<P>Some of the problem are misdiagnosed when a 180 thermostat is installed... you think that solved the problem, if the thermostat was bad, a good 195 would have solved the problem.<P>I checked a thermostat that came out of my 1991...I was fine at highway speeds but when slowing in town the temp gage went to 3 o'clock. The original thermostat was not opening until 205, causing the problem.<P>Your stalling problem is probably not directly related to the temperature reading.

Could make a WAG and say that the fan turn on temps are located at or near 8E3h-8E6h (see archives for more than you ever wanted to know) but truth is that I do not have any '91 Reatta PROM dumps so am guessing.<P>The bottom line is that you need a reprogrammed PROM.

GM cars will crank/try to start reguardless of engine temperature. It is common in a "hot soak" condition to shut the engine off and have the temperature at the sender increase by 20-30 degrees while it is sitting there. <P>When the engine is running, the coolant does not stay in the head long enough to peak but when turned off, it no longer is moving. It will drop back down as soon as the engine is started and the coolant begins to circulate.<P>There is no "temperature inhibit" on the starter - something is failing.<P>Now when you say it will not restart do you mean it cranks but does not start (ESC likely) or does not turn at all (starter/solenoid).

What is everyone's thoughts on why her car won't start when it's above midpoint on the temperature gauge? I don't recall if anyone mentioned this above but Reatta's do not have a failsafe that would inhibit the car from starting due to the temperature gauge being above midpoint. Your car should start even if it is hot. Maybe Ignition module??? I've seen fuel injectors that are bad only when they're hot but wouldn't it be unusual to have enough of them be bad for it not to start?

Indy makes an interesting point. If Rita has been running hot for a while, she may have compromised what has been called the green sticky goo in the module. On my 90, I opened the module to find that the insulating "goo" had softened so it had shifted forward because the module is canted down in that direction. Disassembling compromised the gasket, so it started to leak. The car started and ran, but I suspect that had I not changed the module, I would have been in for trouble at some point. It may be worth checking.

Just a simple observation. At one time I had some wierd temperature gauge high/overheat readings on my 1990 but the vehicle never seemed to actually be overheating. As I was around 90,000 miles, I did a precautionary cooling system overhaul, but saw no change. Six months later (I only drive 2,000 or so miles a year) the ECM gave out. No gauge problems since (two years or so ago).

Unlike my two 89's I have managed to avoid replacing the 195* thermo. w/ a 180* in my 91.<BR> Temp here is somewhat cooler than it was farther south but have seen 96* several times.<BR> Car generally runs at 12 O'clock and has never passed 2 o'clock and then has recovered once I see 40+ MPH.<BR> I did boil out w/ a bottle of flush, drain and flush several times and replace antifreeze.<BR> But I have yet to be caught in heavy, slow or stopped traffic at high outside temps.<BR> Wonder how Rita solved her problem?