No, that is not a safe assumption. There's no reason why you should have any head gasket related problems down the road, as long as the shop does a good job - checks for warpage before reinstalling the head.
How come the work warranty only range from 1 months to 3 months the most and have a lot of disclaimer?
Because after I install it and you leave I have no idea if you are going to take care of the car or beat the snot out of it.
If something is going to go wrong due to my work it usually will happen real quick.
Fair enough. Would you say then if I drive the car in 2days and never develop a problem that it is back in the original state?
Hard to say. When I did engine work like full builds or head work I always told my customer to drive it normal but also to put some miles on it. That way if anything went bad or caused a issue I could try and fix it before it got worse.
I never had one come back but I always wanted to make sure the work was done well. Every car that had major work like that done to it puts a big bullseye on my rep and I had my own shop at the end of my auto days so that meant a lot. Word of mouth was 99% of my customers after the first couple months.
With head gasket problems, a lot can go wrong besides just the gasket.
Biggest issues could be:
Cracked / warped cylinder head
Possible cracked engine block (very rare)
Crankshaft bearings can be damaged depending on
how much coolant got in and how long motor was
run after it did get in.
In a car like yours, with that kind of mileage, compression
may be down due to wear, so a full engine rebuild would be
best, but most costly. Benefit: You get a motor that would go
another 200K miles.
And with any head gasket job, be sure cooling system is flushed
and filled with fresh antifreeze, new water pump, t-stat, rad cap.
Was the water pump and Thermostat replaced when he did the work? If not do that first.
If you had coolant in the oil and ran it for a few days, the bearings may already be damaged. Antifreeze destroys bearings. That's assuming you had the correct mix of antifreeze and water.
WIth 200k, I would probably get a new ride, especially with the symptoms you describe above. The broad temp fluctuations aren't good, you probably have an iron block and aluminum cylinder head, and the constant variations in temp causes issues, due to the dissimilar materials expanding at different rates. Cracked plugs indicates extremely high cylinder temps. I will bet the head is warped at this point.
the head was sent to an independent shop and was declared good.
you have a 240sx, where those stock motors are always being trashed. Mainly because people doing motor swaps. I would of just gotten a lower mileage whole motor and paid to swap it in. Most KA24DE motors i've seen run about $500-750. This swap is pretty direct with a lot of room so $1000 for the swap. Maybe have the guys put in some new parts while its out of the engine and get it all said and done for $2000.
like everyone is saying replacing a head gasket is a little more then just replacing the gasket. Like checking the head to see if its still straight and the pistons. New head bolts are very pricey. Along with figureing out why it overheated and blew.
Maybe the radiator was the reason why your gasket blew.
Before I took the car to him the symptoms:
1. car ran rough
2. overheating after 10 min of city driving but it will stop and go back to normal when its on the highway.
3. milky stiff on dipstik
4. smoked for 10 minutes.
5. plugs cracked.
How many miles did you drive the car in this state?
There are usually other cause that made the head gasket go. How do you know it's not the radiator?
Have you look at the radiator since the mechanic says it's leaking?