overheating

[Guest Recian]

I finally got my intake gaskets back on and fixed all my coolant leaks and went for a much needed drive. Turns out now it's overheating. The previous owner had the same problem and put a sensor in the radiator that ran to the cooling fans to turn them on cuz he didnt wana diagnose the real problem. Now i have to deal with it since his gave out. It's reading 220+ on the gauge but in service mode the engine data reads 103 so i can assume that's why the ECM isnt turing on the fans but are there 2 sensors for the gauge and fans?

[Ronnie]

You car could be working normally. Read this:

Why does my engine run so hot?*-*ReattaOwner.com

To remedy the high temps you can install a lower, 180 degree, thermostat and reprogram the EPROM so the fans come on a a lower temperature. You could also do what I did but the reprogramming is better if you can get someone to do it.

Coolant Fan Control Relay Modification*-*ReattaOwner.com

[Guest Recian]

that's good to know. Im used to imports running about 175-190. Didnt know it was meant to be over 200 cuz my gauge reads H at 225 and that's as high as it goes lol but the ESM says the ecm is supposed to turn on the fans at 214

[Ronnie]

It should cool down when cursing at highway speeds. If not you should check out the radiator for getting proper airflow or internal restrictions. Have you installed a new thermostat? The FSM shows it installed upside down so watch out for that.

[Rawja]

BTW, the reading given in service mode is in Celsius rather than Fahrenheit hence the seeming discrepancy in the numbers.

[Guest mongeonman]

I think you could have air bubles in the cooling sysytem,you have to remove air in the cooling system when the level gets low and you had some coolant.

[Guest Recian]

finally got it figured out. the guy had removed the relays and i put them back in the right spots. After it was still NG, checked the fan connector and power was shorted to ground. Repaired the wire and now she works great. fans come on around 225

[Barney Eaton]

Since you are unsure of your problem, try eliminating some of them.

The relays for the cooling fans are located in the relay center in front of the air cleaner.

Relay "G", "C", and "D" control the fans.

First verify that the fans work.

To test the one in front of the radiator, put 12v to pin 1 on "G" relay socket and ground pin 1 on relay "C" socket... the fan should run.

To test the fan on the engine side of the radiator, put 12V to pin 4 of relay "D", the fan is already grounded.

If that is OK, test all three relays, you will need at least a multimeter, 12v light bulb with leads and a source for 12V. Depending on what you have in your shop will dictate how you choose to test them...... there is a schematic molded or stamped on the side of the relays.

Also check Fuse 20 it gives 12V to the coils for all the relays.

Unplug and replug the connector on the engine temp sending unit, this will clean the connection.

If you have or can borrow a indirect temp reading devise, that will give you a better idea of the actual tempature of the radiator, and engine at the thermostat housing.

If you have not replaced the thermostat, that could be part of the problem. It could also be the block temp sending unit but it is not a common Reatta problem

Last, The engine block temp sending unit communicates with the ECM and it send information to the BCM which then displays it on the CRT. Any of the connections between these computers could be dirty and giving you a bad reading. And it could also be the ECM or BCM acting up.

[padgett]

Most here know my opinion that anything over 200F is Too Hot. All of mine are reprogrammed/thermostat changes to run between 179 and 183 with the HIGH fan coming in at 189F (seen occasionally on really hot days usually at a long stoplight at the Interstate exit).

GM has been using 195F thermostats since the '50s primarily for heat in Really Cold Places (I find a 180F in a 3800 will roast you out even at 0F).

Of course the most GM ever cared about was "5/50". For all Reattas that ended in the last century. My experience is that at 180 not only does everything under the hood from the battery to the belt lasts longer but the a/c also works better. YMMV.

[Guest Recian]

where would you get the ECM's PROM flashed to change that?

[padgett]

Ryan at Sinister can. I have the equipment but not good blanks (and a pile that need new PROMS). BTW I also raise the idle from 650 to 725rpm (10%) to spin the a/c compressor a little faster at a stoplight.

[Guest reatta1991]

Maybe I missed the particular archive that has this info, and if so I apologize about bringing it up again. But when forum members talk about the temperatures of 180, 195, etc., how do the non-techy types like me (with no instruments or gauges), equate those to readings on the pseudo-analog Reatta gauges with bars, but no numbers? Is the 12 o'clock position the thermostat temperature? Is each bar on the gauge "so many degrees?" Or what?

I'm just curious, as my '91 tends to heat up on hills or in traffic, with the AC on. The hot light never comes on, and it cools back to the 12 o'clock position a few minutes after cresting the hill or getting back up above 50 mph. But I get nervous watching the gauge go up, without knowing how hot it really is...

Any info will be appreciated.

PS the thermostat has been checked and is OK, plus the coolant has been changed and the fans are both running when I open the hood.

Edited June 24, 2011 by reatta1991
Add additional PS information. (see edit history)

[Guest Recian]

Sounds like poor heat transfer, I'd check the radiator or the water pump. If the pump isnt pumping at idle but pumps more at high rpm (50mph+) or if the radiator is plugged and the fans cant push/pull enough air to compensate then it'll overheat. Also if it overheats under engine loads (hills) sounds like the coolant may not be good enough to transfer heat anymore, may be a good idea to change it if you havent done so recently, making sure it's got the right mix of water/coolant

[Ronnie]

Reading this might help:

Why does my engine run so hot?*-*ReattaOwner.com

[Guest reatta1991]

Thanks for the info!

Unfortunately I forgot to mention in my PS above that the water pump was just changed a week or so ago, its bearings started to rattle pretty bad, and we might not have made it home from Ohio. So that shouldn't be the issue in this case. The car doesn't overheat...at least it hasn't so far, and I've put nearly 18,000 miles on it in two years.

Maybe it's not a problem...just a concern?

Kinda makes you wonder what really is going on in the cars with only the old "idiot light" temperature indicator (like my '67), doesn't it. Back then, we never knew/know what was/is really going on under the hood. A gauge is much more informative, even sans actual temperature readings.

[Guest reatta1991]

Thanks, Ronnie. Very good info. I suspect it may not be a problem, just a concern. Do you have any feel for what approximate temperature in degrees is represented by the 12 noon, and also the 3 pm, position? It just kinda makes a person nervous watching, as it keeps climbing up to that point on a hill or in traffic.

[Guest Recian]

I need to put a temp sensor in mine. Every time i fix one thing another breaks. Now that i fixed the stalling the temp sensor will stay around 150 then steadily rise to HOT after driving 15 mins or so then sticks at 118. Get out and open the hood and i can grab the radiator it's warm but not hot. They run around 225 which is warmer than im used to

[padgett]

One thing I have always had from my first Jags in the early '60s to today, is full instrumentation even to dual (one for each bank) CHT readouts on my Corvair. Am getting to be able to live with out an oil pressure guage but is difficult.

Am also something of a fanatic about running engines cool (and that means if I have a 180F thermostat & fixed fans I expect it to stay between 179F and 183F when moving (transients to 186F-189F at stoplights particularly when coming off an interstate are OK).

If I want to know exactly on one of the '90s, I go into diagnostics since each segment in the pseudogage is more of a range than a value (straight up seems to be anything from about 180F to 200F, the range I consider the most important).

Being more explicit, GM guages have never been linear and the Reatta is a map, not an equation: The ECM reports the coolant temperature reading as a single byte in the ALDL data stream. The BCM takes that value and does a talble lookup - if between 82C and 94C then the "straight up" indication is lit.

Keep in mind that the original GM CCC CPU did not have a "multiply" or "divide" command but did have "compare" so just about the whole program is table lookups. Certainly the dashboard is. Want kilometers instead of miles ? It just shifts to a different table.

[Ronnie]

Thanks, Ronnie. Very good info. I suspect it may not be a problem, just a concern. Do you have any feel for what approximate temperature in degrees is represented by the 12 noon, and also the 3 pm, position? It just kinda makes a person nervous watching, as it keeps climbing up to that point on a hill or in traffic.

You can read the actual temperature (in degrees Celsius) by entering computer diagnostics and select "ECM Data", then look at ED04, coolant temperature.

Diagnostics Instructions Page 6*-*ReattaOwner.com

How To Access Trouble Codes - '90 & '91 Models*-*ReattaOwner.com

[Guest reatta1991]

Thanks, Padgett...very interesting. So that's why to read the speed in kph you push the button - it changes tables. Gone are the days of a sending unit and a wire!

I'm not a tech type, but would an auxiliary fan hooked up to run on 12 volt all the time the engine is on be something that would help? (I'm not comfortable with trying to get PROM's reprogrammed or jumpering relays...what I don't know might end up disabling the car. I don't need to go there...)

[Guest reatta1991]

Ronnie, will ED04 show up on a '91 or does diagnostics just give error codes? I haven't gone into that because I haven't had any reason to up to now!

[Ronnie]

To be honest I've not had any dealings with a '91 model but I believe they would be the same as the '90 models as far as reading the data in diagnostics. Maybe someone will chime in and correct me if needed. I don't think you could hurt anything by taking a look.

[2seater]

'90 is the same. Actual coolant temperature is available in diagnostics and can be accessed on the move.

[Guest reatta1991]

OK, tried reading the diagnostics this morning and had it activated while "on the move." In normal driving with AC on, in 84 degree weather, the temperature runs around 93 to 96 and is straight up on the dial. When "worked" and then parked and idled for 10 minutes, it went up to about 108 and the pseudo-gauge was at the 3 o'clock position, where I saw it on the hills a couple weeks ago. Both fans were running - I checked them. After shutting it down, the temp spiked to about 110...at that point, I gave up and went inside.

Now that I know I can watch the temperature without putting in an auxiliary gauge, and that those temperatures are not as serious as I initially thought (I traditionally get nervous seeing a gauge that close to the red zone) I'll continue to watch it for a while before doing anything further.

Thanks for all your input, and the good instructions on ReattaOwner.com!

PS found that I currently have no active codes and only a couple of history codes...that's a good thing!

[Ronnie]

OK, tried reading the diagnostics this morning and had it activated while "on the move." In normal driving with AC on, in 84 degree weather, the temperature runs around 93 to 96 and is straight up on the dial. When "worked" and then parked and idled for 10 minutes, it went up to about 108 and the pseudo-gauge was at the 3 o'clock position, where I saw it on the hills a couple weeks ago. Both fans were running - I checked them. After shutting it down, the temp spiked to about 110...at that point, I gave up and went inside.

Now that I know I can watch the temperature without putting in an auxiliary gauge, and that those temperatures are not as serious as I initially thought (I traditionally get nervous seeing a gauge that close to the red zone) I'll continue to watch it for a while before doing anything further.

Thanks for all your input, and the good instructions on ReattaOwner.com!

PS found that I currently have no active codes and only a couple of history codes...that's a good thing!

Your readings are within the range the factory considers normal. I'm glad you find ReattaOwner.com useful.

[Guest Recian]

Mine will get around 110 in the diagnostics but in NC it's over 90 degrees every day. The gauge reads between 220 and 245 depending how u drive it. In D holding the break under max load it'll get about 250.Sucks that the cars normal running temp is 5 degrees shy of HOT according to the computer

[padgett]

Just say no. Last year when I pulled the white coupe back from Gainesville on Interstates at 90F+ & dual a/c on MAX the TranSport (3800) stayed under 185F. Have crossed the MontEagle pass at midday in July with a 4,000 lb 400cid station wagon pulling a 6,000 lb trailer and stayed under 200F.

My experience is that given half a chance, the 3800 wants to run cool (unlike a SBC). Give it a quality (some do not hold within 10F of setpoint) 180F thermostat and decent airflow not over 100F through the radiator and a 3800 in a Reatta will nail itself on the thermostat opening point. My '90s keep teetering between one under the midpoint and the midpoint.

This is not a "special case", I have the 88, two '90s, and the '92 TranSport all 3800s that act the same way and we are now in the period of 90-95 OAT every day.

Also not a new thing, I have been running cars - street and race - cool for decades. Not that hard just everything needs to run properly.

[Guest reatta1991]

Though a response is way, WAY overdue on this, I've waited till I know everything is straightened out and working properly.

In 2011 I got involved with a move to a new residence, and the overheating issue festered. Last year (2012) I didn't drive the '91 much during hot weather, because of it. Early last fall, my mechanic found that one of the two fan motors was ailing. I had that replaced, which seemed to fix the issue for a week or so, and the needle stayed in the center, where it should be...

But that good feeling was short lived...at that point a new problem showed up. When I drove on level ground at 55, the needle stayed centered. But at 60 it heated up a notch, and add another 5 mph and hills, it went up two notches. Slow down to 50-55 and it went back to centered. With AC on, the gauge went up while idling at lights. Fans were checked and operating properly.

Back into the forum, I found suggestions that it might be the thermostat stuck partially open. A quick replacement later, and my problems all went away - though the weather was cooling off and I couldn't be certain last fall. But we've had some upper 70's weather so far this spring, and I've pushed it up to 70+ mph to test it - the temperature needle stays centered, as it now does while idling. That new thermostat seems to have taken care of the problem...thankfully.

Now I can think about working on some appearance issues!

I appreciate all the suggestions, and also just the fact that the forum is here for research purposes...it's a valuable resource! Thanks to everyone involved...