Cadillac Owners Forum banner

Damn! High Oil Temp and alarms? Here is a fix for it

151K views 211 replies 58 participants last post by  matt2thepoint 
#1 ·
I know that many have had problems with their Oil Temps reading incorrectly.... Mine has been acting up lately, and after the 3rd dealer visit, it still went off on me today on the freeway. It seems to stay ok until warmed up (approx 30 mins) then jumps up to around 240-250 then if I slow down/stop, or Turn on the A/C it Jumps up to 300 and Ding Ding... SOOOO ANNOYING! Its weird because it seems to be Steady, but high, until i come to a stop, or turn on A/C, The dealer has done the Ground Fix, 2 times at one dealer, and 1 time at another... I got off the phone with them and want me to bring it back on Monday. Seems like my car is at the dealer more than at my house :crybaby:
Anyone Ever Resolve this Issue?? Anyone have the same problems when turning on their A/C?? I would just ignore it, if it wasnt for that stupid Chiming Sound going off!
 
#84 ·
All these bogus temp numbers are pretty scary not knowing if we are cooking the motor or not. I know on my aircooled cars with dino oil if I ever reach 250 I have to turn it off or risk bearing damage by going higher.

After my V hit 285 the dealer said it was a bad sensor and replaced it.

I am picking up my V today and I have yet to find anyone at the dealer that can give me a straight answer on what the maximum oil temp should be for the V.

Anyone know?
 
#87 ·
I have yet to find anyone at the dealer that can give me a straight answer on what the maximum oil temp should be for the V.

Anyone know?
The V is no different than any other engine, in that it's pretty hard to define what exactly the highest allowable temperature is. Somewhere in the 280-300F sustained temperatures at the bearings is probably not good, as even good synthetic oils are going to start breaking down somewhere in that range.
 
#85 ·
Anybody know what ground the oil pressure uses?
 
#86 ·
Oil pressure sensor uses the ground on the back of the head.

However, that may not "fix" the problem as a bad ground to the frame may set off the reference voltage used in the PCM so you may still get errant readings.

If you can use a DVM, connect one lead to the battery negative and then measure the voltage drop (in millivolts) at the HEAD of the bolt (usually a 15mm) securing the ground connection..

Should be less then 50 millivolts with everything on (lights, A/C).
 
#88 ·
Thanks heavy

T/J over
 
#93 ·
I did the star washers on the fender/chassis ground and the passenger side head ground last night. Sanded some paint off the fender one, and sprayed Caig PreservIt contact cleaner/preserver on both. I most likely won't drive the car until Sunday as I head to Summit Point, and then Monday will be the true trial by fire. At past track days I've pegged the oil temp gauge at 329F within probably 10min or so each session, so I'm curious to see if fixing this issue is/was as simple as improving the contact for those two grounds.
 
#95 ·
Looking forward to hearing about your results. And check it on the highway, that's when mine gets bad.
 
#96 ·
Heavy was 100% right... We fixed the grounds and my temp went from running in the 300s and dinging like a mofo to 200s-220s SIMPLY by fixing the ground on the back of the heads and the right part of the engine bay...

KUDOS TO HIM for finding this and saving me a headache (I was about to drain oil and start replacing sensors!). When it comes to electrical, heavy is my guy!

Reed-out.
 
#98 ·
Thanks Heavy:thumbsup:

My oil temp has been running up to 300 for a while but it's been really bad since we've been in the mid 90's for the whole month of June. I checked the voltage and it was running 250mv. I pulled off the bolt and sanded everything down and it went down to 110mv and after a 15 minute spirited drive my oil temp held steady at around 200*. I was hoping the voltage would of dropped a little more but it's fixed so I'm happy. I did not do the bolts on the back of the heads only the main ground on the the right side.

I've been putting this off for a while because I thought it was going to involve pulling the sensor, but this took all of 5 minutes. I feel like a dummy for not doing it sooner.
 
#100 ·
As I was changing my spark plugs, I found another ground. I had my coil packs off, otherwise I couldn't see it. It's on the back of the passenger side head right above the last plug.

So I finally put a star washer on the fender wall ground. I scratched some paint off, but need to get back in there and do a better job. As is, driving around town with AC and lights on temps were very steady at 222. It used to bounce around 5-10*.
Didn't pay attention to highway temps (this is when mine starts to climb) cuz I was focused on something else.

I'm getting closer every time I mess with it and will post up when I have more to add.
 
#101 ·
I'm going to check into this too.
I'm sure you guys in the yellow group noticed me at V Day during 1 session just puttering around at 50.
My oil temp had hit 302 and the alarm was going off so I put it into 5th and just cruised for 2 or 3 laps.
I don't think it was an issue with the sensor as the track temps were probably over 100 and I was winding 3rd into the rev limiter quite often.
I did manage to get it to drop during that session and once it sat for lunch it was fine the rest of the day.
I'm guessing the rain cooled the track down plus I was shifting into 4th before redline.
Still something I want to look at tho...
 
This post has been deleted
#103 ·
CRAZY hot the next couple days. If I'm brave enough to go out, it should be a good test.

Turn on the A/C, and the lights for the "acid test".:highfive:

Pretty interesting to see that much drop huh?

This is a major problem with the high tech electronic monitoring systems in autos.

Ground referenced (single ended) measurements can change when the ground reference is different as the PCM is using "frame ground" and the sensors are using "engine ground".

The sensor sends a variable 5 volt signal to the PCM which got offset almost 1/2 volt (in Reed's car) because of the bad contact.

Because of the low current the sensor draws, the biggest offset it could generate is minimal though its' ground.

To put is simpler, the voltage is correct coming out of the sensor.
The "ground reference" the PCM uses for measurement gets "tricked" by the bad connection into reading a false high (sensor output + offset).
 
#104 ·
Thanks for the tip! I was dinging all over place yesterday and for the past 5 years. I applied the fix about 20 minutes ago and IT WORKED! It seemed too simple a fix to actually work, but it did. Just before I applied it, my temps were hovering around 270 with out the ac and off the chart with the ac on. right after the fix, 218 without the ac and 224 with the ac. Its 94 in NYC and it's 69 in the car! :bouncy:
 
#109 ·
Took a two our trip in the evening. It was 85* and the temps were in the 220 range for a while. Turned on the fog lights (A/C on but not headlights) and it quickly rose to high 250s. As soon as I turned off the fogs it instantly dropped back to 220. However, by the end of the trip with A/C and headlights on she was up around 240. This is consistant with last weeks trip. That one was only with the A/C on.
When I get the chance, I'll clean up the connections on the startert. They were pretty bad last year, and my voltage in usually in the low 13s.

Tony
 
#110 ·
Heavy,

Yesterday I pulled off the bolt under the hood support and sanded the paint, cleaned up the battery terminal and my problem is gone. Today its 115 outside and i just turned on every light possible and the AC on high and the temp doesnt bounce around anymore. Thanks again

Derek
 
#111 ·
Ok so I measures the the voltage drop at the ground on the side with everything on. Not too bad at .130 mV. I went ahead and cleaned the paint off and added the star washers. Looked around for some more grounds. Found two ground wires broke off at the back of the DS head. I fixes those and star washered them too. Found another ground up by the computer and star washered it as well. The temp no longer bounces all over the place but I still get a spike when I turn on the A/C and lights. I can also make the temp decrease when I slide the dimmer down when the lights are on. Anybody have anything I could check? The only grounds I haven't checked yet are on the PS head. I'd like to put this crap to bed and thought I would by fixing those broken grounds but it didn't work for me.
 
#118 ·
#114 · (Edited)
"Right under the hood support", as stated in the sentence you quoted. There's only one hood support, so I'm not sure I understand what more information you're looking for.

Left edge of this picture, the bolt right next to where the hood prop attaches to the fender. You can see the thick black cable running to it.
 
#115 ·
Fudge!!!

Hot assed summer! Oil temps are still a bit off, but no where near 300.

Well, I went to the track yesterday. It was in the low 60s, so I figured I'd be fine. WRONG, after a few hot laps in the first session it started gonging. FYI it was still jacket weather at this point lol
Normal driving it's between 225 and 245.
 
#116 ·
Strangely enough, at V Day 4, when it was hot as hell, I didn't get any alarms until the final session. At VIR 2 weekends ago, with ambient temps about 20F cooler, I was getting the alarm every session. I wasn't pegging it at 329F like I used to, but it was getting into the 3-teens indicated. My cruise temps are the same as yours (in other words, too high).

Later this week I'm planning to temporarily install an Autometer gauge reading oil temperature from above the oil filter, where the Vettes (and F bodies?) had their temp sensor. Just waiting on 12mm-1.5 to 1/8" NPT adapter so I can put the Autometer sending unit in place of the Vette sending unit.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top