98 Seville overheats. Replaced radiator, water pump, thermostat (twice), radiator cap, checked heating core for blockage (water ran through it without a problem), fan speeds high and low both work. Idles fine with no overheating, but driving down the road within 5 minutes, overheats. When we get home fluids pushing out cap. Reservoir water extremely hot. Upper hose extremely hot, but yet lower hose seems to be cool to touch. Replaced thermostat twice! No fluid appears to be in oil. No fluids coming out exhaust (except standard condensation during warm up). Any thoughts?

 

you will most likely find the answer within this FAQ

https://www.cadillacforum.com/m_7193/tm.htm

 

Make sure you have the proper mixture of anti-freeze in your engine.

Sometimes you can have a core that may be getting clogged intermittently, try bypassing it. Just connect upper heater core hose together with the bottum heater core hose. Hose clamp a peice of copper tubing between them. It dosen't cost any thing to try it. It might just fix your problem. With all the sealant pellets that are put into the cooling systems of the north star engines, the heater core and radiators are good canadates for bad cloggs that flushing dosen't cure for long, if at all. If you do bypass the core make sure the hoses aren't kinked off, route them so the fluid can flow freely through them, also be carefull removing the spring clamps on the heater core because the core end is made of a plastic composite that can break easily.

 

Thanks for the replies so far. Has anyone actually tried Block Chek and/or the stuff that is advertised on this site for the gaskets that supposedly patches them up or something like that?

 

the test kit is pretty standard to spot CO in the coolant.
if you have the test done by a shop, be ready to pay more than the $50.

the liquid resin has been used many times, some with success, some with failure.
it is a gamble to avoid an engine teardown costing thousands .. not sure i use that
on something like the Allante or a Series-V car, but for a set of wheels, to get
around town, why not .. at the very worst, it fails and you are back to an engine
teardown.

keep us informed ..

 

We used the test kit and found it is probably a head gasket problem. So we will try the additive to see if it can temporarily fix the problem. Is there any specific product that anyone recommends for this? Some products we have read about say not to be used on the Norstar engines. So we're looking for which products might work?

Thanks!

 

sorry for the bad news.

will you please keep us imnformed as to the outcome?
we are seeing a great deal of this type of problem.

also, do read our FAQ on Dex-Cool ..
you will most likely find prevention there.

thanks

 

 

it can happen.

it is not uncommon to have a head crack and then the gasket fail after the crack.
The act of a head cracking is however, rare ...

how do you find out? teardown the top end and inspect.

note:
i have seen numerous complaints of headgasket failures,
but fewer of cracked heads. the N* designe can take a
whole lot of overheating, but not so much quenching.
if someone added COLD water in a overheating condition,
she would go CCRRRAAAAACCCKKKKKKKKKKKK !

 

I had the same problem and I also have a 98 STS. I changed all the components of the cooling system also. I have a posting called 98 STS problems on this forum. I used a product called K&W nanotechnology head gasket and block sealer on mine and it worked for me so far. Its been 2 weeks and the temp gauge has not exceeded the normal temp. line.
I bought it at auto zone for around $20.00. they also have a double your money back gaurentee so if it dosent work you at least get your money back plus $20. Its worth a try.
good luck.