Seems there are a fair number of these cars listed with overheating issues. Most of the time the seller lists as a minor problem, it's not. Read on to find out why.
Most of the time the engine that has this problem is the Northstar. Overall this is a great engine and is listed in the top ten best engines. However, they are very expensive to repair. Overheating is a symptom of a larger problem, in other words, the overheating is not the problem, why it is overheating is.
1. The Northstar has a feature known as "limp home mode." This feature allows the car to be driven without a drop of water for up to 100 miles. It accomplishes this by shutting down the cylinders in an alternating fashion, this blows outside air through the engine, hence the engine becomes air cooled instead of water cooled. You need to know that if the car is driven at high speeds or longer distances, internal engine damage will result.
2. Overheating can be due to a myriad of things, here are a few: Blocked Radiator-usually caused by excessive dirt buildup. This is fairly easy to see and very easy to fix. Thermostat-these are designed to open and allow water through at certain temperatures, if it is not opening, overheating will result. This is rare on these cars. Clogged Radiator Inside-look inside the radiator (if you can, later models are sealed) if you can't, then look in the coolant canister, if the water or canister (if it is empty) looks muddy, usually means a sealer has been put in, this is DEATH to these engines as it clogs up the internal water ports. Head Gasket-this is fairly easy to diagnose, look at the base of the heads (will take a flashlight and some effort) if there is leaking here, the gasket is blown. Look at the oil on the dipstick, if there is antifreeze there, or if the oil looks milky or if the oil has bubbles in it, this could indicate a blown gasket, it can also indicate a cracked block. Fans-these cars have at least two fans on most models, crank the car and let it idle, the fans should come on shortly, if they do not, it is probably a relay, if one fan comes on and the other does not, it's likely the fan motor.
These are just a few of the things you can see for yourself. Be aware however that if the car will not crank and the seller tells you it was overheating, you can plan on a new engine. This will cost you about $4,000.00 for the engine and around $2,000.00 for the removal and installation. Also the intake manifold on the Northstar is plastic and cannot be repaired, it is not included on the new engine, so plan on buying one. Of Course, you can buy an engine on ebay for less, but it will still cost you to swap the bad one.
There are times when some may want to purchase anyway, thats fine as long as you know what you are getting into. If the rest of the car is great, then it may be worth a new engine. Most sellers will only discount the car $500.00 to $1,000.00 though, thier reasoning is that it is a simple, inexpensive repair, 99% of the time this is just not the case. Nothing on a Cadillac is cheap. If the car is book valued at $6,000.00 and it is going to cost you $5,000.00 to fix it, you would be better off looking at another car or offering the seller $1,000.00 for it as is.
These are just a few tips. If you have a question or if you would like to know how to run a diagnostics test on the car (you can do this without any special equipment) feel free to email me.
One more note, I am not slamming the Northstar, I have an STS that runs perfect, the key is that the engine MUST be properly and meticulosly maintained.