1996 Fleetwood Brougham - strange issues

[tajis]

I recently purchased a two owner 1996 Fleetwood Brougham. The car has around 119K miles and is in above average condition (minor interior issues, good body/frame, etc).

I drove the car a few days until one day I noticed that it would have trouble starting. A SES light popped on and the error code said it was a temperature sensor (waterpump sensor) issue. I hooked up a monitoring device and my coolant temp was showing as -40 degrees. It's not quite that cold outside LOL! Anyway, I let the car idle awhile and the sensor did kick in once the coolant temperature was around 80*C. Problem is that it started to boil coolant out the plastic tank before the radiator fans kicked in.

I got in there and flushed the system, tried pulling the thermostat, and ruled out a head gasket issue.

I swapped out the sensor and the new sensor worked for a few days before doing the exact same thing as the old one. The car has trouble starting and runs very rough until the sensor reads 80 or so degrees and then everything smooths out. I swapped out the radiator cap and this helped the idle temp go up to 95*C before boiling over, but the fans still didn't kick in. I know at least the big electric fan is working since I can wire it up to the battery and have it kick in, but the smaller fan never kicks in.

I'm new to this car and its quirks. I would appreciate any advice on how to get this issue resolved.

The first few days it handled like a dream. I hope to be able to get it on the road again soon.

[KHE]

The LT1 engine does not have headgasket issues like the Northstar engine - apples to oranges as far as comparison goes. The majority on this board have Northstars so you'll hear a lot about headgaskets but it does not pertain to the small block Chevy engine in your car.

The secondary fan rarely kicks in unless the coolant temperature is greater than 231 degrees - that is not the problem. If the primary fan does not kick in, the issue could be a bad primary fan control relay located in the underhood relay center. I believe there is also a cooling fan relay in the same relay center.

Where are you buying the temperature sensors? Does the code reset after replacing the sensor?

Is the thermosat back in the engine or is it still out?

[tajis]

Thank you for the reply! I bought the temperature sensor at Autozone. It ran about $10 and screwed in to the front of the water pump. After changing it out like that, as I said, the engine was fine for a few days and the sensor worked great. I had a temperature readout on my OBDII device and the error code stayed off. I left the thermostat off basically to see how the engine would behave without it.

I noticed, however, that the coolant was still boiling over if I left it at idle long enough. The temp showed as 95*C before I saw coolant boiling out and I cut the engine off to let it cool down. When I cranked it back up it had the -40*C thing going again, so I'm not sure if somehow the computer is acting up or I managed to burn out the sensor (which, just like the original, gives an accurate reading if it gets to 80*C or so). Right now the thermostat is off and I've pulled the battery to let the computer reset over night.

With the -40*C thing going on I can barely get the car to crank or idle until the sensor kicks back in. The big fan runs like crazy until I get an actual temperature readout, then it shuts off completely and never comes back on. If I unplug the sensor wire I get the same effect.

Glad to hear that about the head gaskets! The only GM engine I have experience with is the 3800 so I appreciate the info.

[rockfangd]

welcome to caddyinfo forum.

I like the GM 3100-3800 series.

This may be a stupid question but did you inspect the pigtail to the Coolant temp sensor? They have repair pigtail because they are prone to corrosion. Faulty CTS readings will cause all sorts of havoc.

I prefer to stick to oem on the sensor itself because I find the cheap ones rarely last and are sometimes out of spec right out of the box

[Logan]

The -40F is kind of a default mode in the PCM. They never show any colder then that. A open coolant sensor circuit will display -40F on a scan tool.

[KHE]

Measure the resistance of the sensor with the coolant cold and the sensor unplugged and post back the reading. Autozone is not known for quality parts...

You need to replace the thermostat - as long as it is out, buy an AC Delco (original equipment mfgr.) stat.

The computer is the last thing I would suspect at this point. They are very durable units and rarely fail. I still think you have a fan relay issue.

[Logan]

Rereading the post...

"With the -40*C thing going on I can barely get the car to crank or idle until the sensor kicks back in. The big fan runs like crazy until I get an actual temperature readout, then it shuts off completely and never comes back on. If I unplug the sensor wire I get the same effect."

The -40F will only display if....the coolant sensor is unplugged or the coolant circuit is open, or if the scan tool has a software glitch or a bad PCM power or ground. The sensor should not be 'kicking in..'. It should display close to outdoor temperature after a overnight sit. It should never display -40 C or F.

"The fan runs like crazy..." That is a common fail-safe mode for failed PCMs or failed /detected failed coolant sensors.

"Barely get the car to crank.." Something is going on.

[rockfangd]

see what happens is the CTS leans or richens the fuel mixture by what the temperature is read by the ecm. So if it is reading -40f it will attempt to start a full rich condition but it wont run right because the temp is not actually that cold.

I had mine go out on my olds awhile back and it ran full rich. scantool showed -40f and I replaced the sensor with oem sensor. never had another problem

[tajis]

I had some time today to try what was suggested. The thermostat and the temperature sensor were swapped for OEM parts. At first the sensor did not work, so as suggested I checked the connector for corrosion and could find none. To be safe I took a small metal pick and slightly scraped the inside of the connector, then used the pick to bend the pins of the connector inward to get a better grip. As soon as I did this I had a readout and everything seemed to work.

At about five minutes into testing the car went absolutely haywire. The engine revved and was all over the place, then it would behave as if it were about to cut off. The temperature readout, I noticed, was jumping around like crazy. -40, -31, -10, 5, etc. It might as well have been spitting out lottery numbers. I grabbed the sensor cable and wriggled it a bit while pushing on the connector and everything went back to normal as soon as it had a stable temperature readout again. This leads me to believe the problem is probably in the connector or wiring?

As for the fans... The only relay box I could find under the hood was in front of the passenger area and had things like fan fuses, an air compressor relay, etc. Where would the relays be for the fans? I checked all the fan fuses and they were good at least.

I can confirm the fans are not kicking in on their own. I only saw the large, primary driver side fan kick on once for about five seconds. After that it never ran again on its own and would just let the car reach the point of boiling over.

However, there was an interesting exception.. When I cut the heat on inside the car to try and slow the heat climb a bit I noticed that the primary fan would kick on. As long as I left the heat running (at 90*F), the primary fan would run at a slow speed and kick up to high speed every now and then. I ran the car like this for 30 minutes without the temperature exceeding 90*C according to the new sensor. No boiling over. Would this lean toward the relays being bad?

Thanks to everyone for the great replies!

[tajis]

Alright, I feel stupid. I didn't have any documentation and didn't realize the relays were outside the main box under the hood. Here are the results.

Primary fan kicked in when I manually jumpered the connection. Secondary fan was completely dead.

I pulled the fan motor and checked it out. It was completely burnt out and toast. I dug a replacement out of a 90 something scrap LeSabre and it works perfectly. Was an easy swap.

This overheating issue is driving me nuts, though. I can kick on the heat/ac and get the fans to come on, at which point the car will not overheat. The second the fans kick off (from me turning the heat off), the car goes into a slow overheat.

The only thing I can figure, since everything starts boiling out the coolant bottle cap at roughly (as of how tight I have the cap now)102 degrees celcius, is that something isn't holding the pressure it should be. The lines all seem good and the bottle lid seems to go on tight. Do these coolant bottles tend to warp over time? This is speculation at this point since changing the cap did help it significantly as the old cap would barely hold pressure.

The only other thing I can figure is that the engine is actually hotter than what the sensor says. I've replaced it with an official part, so I'm not sure if that would be the case.

[KHE]

Have you tested the radiator cap with a pressure tester to see if the cap holds the stated PSI?

Does the car overheat even when moving or just idling?

Have you measured the resistance of the new sensor with the car cold to compare it with the resistance value at the ambient air temperature?

I would monitor the coolant temp. and observe the coolant temperature at which the fan(s) kick on. If they do not kick on then the issue lies in the control circuits that command the fan on. Having the heat turned on should not have any effect.

[KHE]

Any update on this?

For what it is worth, the 1993 shop manual (different version of the 350 engine) states that if the engine is overheating and the coolant fan is not coming on, the engine coolant temperature sensor has probably shifted out of specification and should be replaced. If the engine is overheating and the cooling fans are ON, the cooling system should be checked.