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Roadmaster 5.7 Operating Temp

07-03-2007, 03:41 PM
My uncle just gave my daughter his 92 Roadmaster with 5.7L engine. I picked it up last night, and noticed that the temp gauge never goes beyond the first notch above cold (140-160). Is this normal? It seems like the high idle stayed for a very long time as well. I am wondering if the car has a bad thermostat.

Also--the oil pressure indicator pegs beyond it's limits, although it comes down when warmed up.

This car is going to a new 17 year old driver--I want to make sure it's in as good shape as possible before I let her on her own with it.

Thanks for any answers or guidance.

Art in NY

07-06-2007, 10:34 PM
I have a '93 and the temp gauge runs in the same area. I changed the thermostat (195 degrees) and it still stays about the same. It went above it once to about 190 while driving in 90 degree weather through the mountains.
Oil pressure - normally shouldn't peg the gauge, but should drop after the oil heats up & thins out. Might be a bad oil pressure sending unit.

07-22-2007, 02:34 PM
I just did a major service on the car-needed a radiator, changed all hoses, tranny service, new thermostat etc. The temp gauge is reading low still, but more concerning is the fact that the choke seems to stay on high idle much longer than it should. I drove the car 20 miles yesterday in 80+ weather and it still idled at 900 RPM in D and 1100 RPM in Park. After 40 minutes or so it dropped down to acceptable levels, but I am concerned it will cause much worse fuel consumption than it already has.

Also--I need a complete set of Body Side Moldings--anyone have any ideas where I might find them?


07-23-2007, 11:59 AM
Also--I need a complete set of Body Side Moldings--anyone have any ideas where I might find them?
The only places I've seen items like this are eBay, and Hemmings Motor News. I think these vehicles are still considered fairly new to have aftermarket replacements available.

07-27-2007, 06:19 PM
You've described two problems my '92 is experiencing.

The Temp guage has been like that for a long time (> 4 years). Since this question was posed, and I had my scan tool (OTC 4000) hooked up last night, I made note of the Coolant Temperature reading. Scan tool reads around 180 (more than the 140-150 normally on guage). I haven't changed to a t-stat other than stock, but when I started using ER (Energy Release) in the oil, I noticed my car never ran quite as warm. In fact, it seems that the temp started reading low about the same time I started using the ER. If you don't have access to a scan tool, but you have the Automatic Air Conditioning option (C68) in your car, you can get the coolant temp from your A/C control head. Though I haven't verified the readings against my scan tool yet, I posted instructions in a thread at a few days ago;f=32;t=001071

As far as the oil pressure guage, mine just started acting up 2 weeks ago. It seems like my problem is more intermittent than specifically going away when the car warms up. The guage pegs at times, but reads normal most of the time. Oh, and neither the scan tool nor your AC unit gives any oil pressure readings. And I just realized there appears to be no idiot lights in our cars with the guages. The light on my AC unit which indicates "Low Oil" only tells you if the oil level in the engine is low, but not if the pressure is low.

08-12-2007, 12:27 PM
Thanks for the hints. I don't have a scanner, but I noticed a couple of things.
First the car never seems to go above 130, or the very first notch beyond cold. I drove it about 12 miles last night and it stayed in high idle the entire time.

This morning I took it out for about half hour and it finally started to slow down as I pulled back into my driveway.

I am not sure it's the actual sending unit any more, as the radiator cap never gets hot either--it remains warm at best.

My kid can barely afford the gas as is, so I think I might have to go to a different mechanic.

Would there be any harm in putting a 220 or 210 thermostat in?

Also--anyone know how to reprogram the compass on the mirror?


08-12-2007, 01:48 PM
I didn't know buick used a choke in 1993. I think you have throttle body injection. Two injectors on top of the throttle body. The otc is reading the temperature of the computer temperature control. This has two wires ond should be on the intake close to the upper radiator connection. If you installed a new 195 degree thermostat and it is working change this unit.
I changed one on a Chevy pickup that was bad and the mileage doubled.
A cracked exhaust manifold close to the oxygen sensor will give you a very rich mixture. Neither problem usually causes stalling. Spray carb cleaner along the intake manifold and the base of the throttle body. A bad air leak will cause stalling. A stuck open egr will cause stalling.

08-13-2007, 01:34 PM
Yes my '92 is the same way sence new always seemed alittle cool but heats fine. The oil pressure always runs on the high side too.
Lucky 17 year old kid. He'll never drive another like the Roadmaster.

09-23-2007, 12:08 PM
OK here is the latest update.

While I haven't had the chance to bring the car back to the original mechanic, my daughter has been driving it, and as I said before, it never gets above about 120 degrees on the gauge. This keeps the high idle engaged much longer than needed, and I am sure as the car is getting betwen 13 and 15 mpg wasting gas.

Since it is cooling off a little around here, we have been driving without the AC for a couple of days, and while the op temp is now the same if not COOLER, I have noticed that the radiator cap never gets hot--even after 1 hour of driving. It gets warm but never too hot to touch. So this leads me to believe that the sending unit may not be the only problem.

Any ideas? This 5.7 should warm up to the 195 setting on the thermostat shouldn't it?


09-23-2007, 12:58 PM
I would pull the thermostat make sure it is closed when cool. Then get an old coffee cup fill it with water and put in the microwave until boiling. Using pliers set the thermostat into the hot water it should open. Many new ones don't function properly and should be checked before installation.

01-08-2008, 11:44 PM
My 95 roadmaster gauge runs darn near dead cold, but I have heat on demand on frigid days. my mechanic thinks the gauge or relay for it is out of kilter.

01-09-2008, 08:11 AM
The sensor works on resistance check the resistance at the sensor in the intake. If this appears good use a copper wire and ground the connection if the gage doesn't move replace the gage.

01-09-2008, 01:23 PM
If any new info needs to be added concerning this issue, can we please start a new thread? This one had run it's course and was dormant for over 90 days before being resurrected. Thank you. Closed.

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