70k miles, replaced radiator, waterpump, etc but mechanic said previous owner took out thermostat to allow water to flow freely and that there was stop leak that he could tell from the radiator cap. After about 20-30 minutes at freeway speeds, the thermo inside the car starts to rise all the way to red at which point I shut it down.

We've flushed the system and I looked at this thread

https://www.cadillacforum.com/forum/...ead.php?t=2445

but I'm unsure how to proceed next as a noob since I don't have most of the tools mentioned. I'll have to have a mechanic do whatever tests need to be done.

The mechanic thinks there is a clog in the system and that's the reason that we replaced the waterpump and the radiator. There is still no thermometer in the hose as he said the previous owner removed it to try and keep the system cool. However, after doing both, it still overheats. I drove it into work today, about 15 miles and it started to overheat so I put the car into neutral for about 10 seconds, after that the temp gauge went back down. (anyone know what that means? )It still started to heat up and when I let it idle for a few seconds the gauge started to climb again in the parking lot. It appears the fans are all good and are working, in fact, when I was in the parking lot they seemed to increase in intensity probably due to the rising temperature. I shut it off so it wouldn't get any hotter.

My question is, what can I test on my own before bringing it to a different mechanic for a costly diagnosis? I have a laser temp gauge and I can shoot the radiator hoses or possibly the head but can anyone tell me which hoses, or possibly where on the engine to see if it really is overheating? What's the temperature supposed to be? I think it was a little under 180 degrees F on the hoses, but again, I'm not sure exactly where I should be aiming the laser. Thanks in advance for the help, I tried to read thru as many posts as possible before posting but I'm confused.

Here's what I have based on the post above

Symtoms? any one or more of the following may be seen..
yes- overheating at highways speeds,
yes - loss of coolant but no leaks,
no, i don't think so- crud in the surge tank / reservoir,
no, but perhaps the level has risen- water in the oil, check the OIL DIPSTICK!
not that i've noticed- white "smoke" (steam),
possible- increasing oil level.
can't tell, fluid sprayed all over when we replaced the radiator- smell of coolant but no visible leak

where are the hoses for this, heater core is in dash/firewall right?- clogged heater core - if one hose is much hotter than the other one your heater core may be plugged,

haven't checked this, how can i tell?- lower radiator hose w/o inner metal support - collapsing,
doubtful, new radiator- clogged radiator,
this is possible, how can i tell- clog or leak in the hose to the purge/resevoir tank,
no thermostat installed- thermostat is sticky. read FAQ on Dex-CoL,
- failed thermostat,
- thermostat installed backwards,
- defective NEW thermostat,
i put a new radiator cap- defective radiator cap,
replaced already- failed water pump,
prob not, mechanic did this and he's done them before- defective water pump with impeller installed backwards,
mix should be right- used water instead of the 50/50 coolant mix,
- used pure coolant instead of the 50/50 mix,
possible- use of tap water instead of distilled water has created deposits,
how to tell?- wrong drive belts,
how to tell?- slipping drive belts,
how to tell?- clogged catalytic, failed catalytic
how to tell?- clogged tailpipe
pretty sure they're running properly- radiator fans not working
how to tell?- engine timing,
how to tell?- air or gas in the system
how to tell?- cavitation at water pump / AIR in system
- rebuilt radiators, cleaned & flushed fail due to weak coolant chamber
vanes that collapse & shut when the radiator gets HOT.
etc ...

other things make peope THINK the car overheats although the coolant temp may be normal:
i hope it's just this, how can i test and or know?- defective coolant sensor
- climbing temp upon hard driving, ie hills, acceleration, headwind, extreme ambient temp.

 

to me that highlighter comment signals a high possibility of failing headgaskets. do the exhaust gas in coolant test done, its cheap enough.
CAUTION: when you are doing the test driving it, MAKE SURE you drive it on the same road and under the same conditions that created the overheat!

the "stop leak" could be simply the GM additive and not stop leak.

replacing pump and radiator is illogical - see all the highlighted comments .. why would he think that was the problem? consider finding another mechanic.


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someone else told me they had the same problem and that it was not the headgaskets, but it was the transmission module which is why shifting into neutral frequently causes the engine temp to go down. can anyone recommend a good place in southern california that specializes in cadillacs to get me a straight answer? on cadillacforum.com someone mentioned jarvis auto repair in san diego, and although i'm in orange county (santa ana) I wouldn't mind taking it there if they can correctly diagnose/fix my problem. Problem is, it might not be worth it. I'm going to call later today and ask how much it would be to replace the headgasket.

http://www.cadillacforums.com/forums...alifornia.html

Also, I do want to do the test for the exhaust gases in coolant, where can I get that done? how much? also, i did a search on how to pull codes from the driver information center because I would like to know what's going on. Is there a decode for the EX codes? I saw a post earlier that they were for cars made in a foreign country but according to the carfax it's been here in so cal all it's life.