2000 Saturn S series overheats

I have a 2000 saturn with 145,000 miles on it. It started to run hot this spring when the weather got warm, and boiled over a couple of days on the way home from work. The temperature gauge was erratic; it would go from normal to pegged right, below C, and back in a few seconds. When the weekend rolled around, I took it to Firestone, and they wanted $1500 to replace the thermostat, the water pump, radiator hoses, brakes, etc. Since they had just done the brakes a few months ago, I took their recommendations with a grain of salt but flushed the radiator and replaced the hoses and thermostat. The engine runs cooler but still gets hot in stop and go traffic. Also, the temp gauge still acts up; today when idling the engine speed would “pulse” up and temp would noticeably go down at the same time. Since both the radiator hoses are hot when the engine has run, I think the water pump is OK. Any ideas? Fan clutch, engine coolant sensor? Could it still be the water pump? Sorry for the long post and thank you for any help.

When it is running hot, is your electric radiator fan running?

I don’t know. Pull over next time and check? It doesn’t run hot on the highway, so does that mean it’s getting enough airflow then?

I might mean that. Checking the fan operation is the way to find out. Be aware that you have two cooling fans on this, one for the radiator and one for the AC. Be sure both are working properly.

It could also mean that your water pump is weak. The impellars can erode and the pump not pump sufficient volume.

It could also mean that your radiator is clogged or has buildup of residue inside…even though you’ve flushed it.

If the fans are working properly, a shop can check the pump out for flow and check the radiator out by thermally mapping it using a pyrometer.

I’ll just add, since mtnbike has this all under control, that you don’t have to pull over to see if the fan operates. The next time you get home or wherever, just leave the car idling and pop the hood. Keep one eye on the temp gauge and another on the fan. If it is working it will eventually come on. If not the temp gauge will keep climbing.

Keep clear of the fan itself - no dangling neckties or anything

If the radiator flush took very little time, say 10 minutes, it was likely improperly done. Cars with reservoirs need much longer flush times - up to an hour - than cars without a reservoir. So your slight improvement may be the result of a slightly less-clogged cooling sytem.
I would take the car to a radiator shop with a good reputation and let them figure it out.

In the meantime, if you can’t do that right away, run your heater on full especially when you are in stop and go traffic. Don’t use the A/C at all. Check to make sure your reservoir is full when the car is running and if you have a radiator cap, when you FIRST start the car and while it is still cool, remove the cap and see if there fluid running level to the bottom of the fill tube. If not, fill the radiator with a 50/50 mixture of radiator fluid (use Prestone) and water until you can see the fluid at the bottom of the fill tube. Do not do this while the car is hot. It won’t solve your problem, but it will help prevent engine damage due to intermittent overheating.

there’s quite a number of possibilities…probably your best bet would be to have someone diagnose the real problem, since I would suggest the guys who already worked on it took the big hammer approach.

if you have something going on with idle speed changing, it would suggest that’s a sensor which is feeding erroneous information to the computer. a faulty temp sensor is a possibility, and one that’s easily checked by a service center.

Have you actually seen steam coming from the surge tank or otherwise? Or is the overheat condition indicated only by the temp gauge?

I’d suggest having the system (and cap on the surge tank) pressure tested. That would ensure there are no leaks in your system. If there is a leak, then the system won’t stay pressurized and can more easily boil, once it boils, then the engine can quickly overheat since boiling coolant won’t absorb heat like a liquid will.

I’d doubt the water pump is at fault, since they just replaced this and the thermostat.

It is possible that your radiator is just worn out (either too much crud inside), or it’s sustained damage to the fins and doesn’t provide enough cooling capacity.

Lastly, don’t also rule out a problem with the engine. A partially blown head gasket or a crack in the head or block could allow exhaust level pressure from the cylinders into the water jacket (since this is hundreds of PSI and your cooling system vents at 15psi), this can overheat the coolant, blow gas into the coolant loop and blow hoses or the pressure cap.

A habitually lean running engine can also make for a hotter than normal engine too.

Did you replace the radiator cap along with the hoses and thermostat? If the radiator cap is not holding pressure, the coolant will boil over at a lower temp. I usually replace both the cap and the thermostat when I do a coolant change.

Ed B.

Sorry for not replying for a bit; but I’m in Denver and we had snow off and on until the 13th, so the temperature wasn’t much of an issue and I had nothing to add. Warmed up last week and the car started overheating again, and boiled over two days running. I tried to replace the water pump myself this weekend. Complete fail – couldn’t get the bolts off of the cover, even after letting liquid wrench soak in for 24 hours. In the meantime, I’ve done something to the tensioner; when I put the belt back on, it’s loose and only gets tight when I crank the tensioner clockwise. Sure looks like it’s threaded correctly to me. I think I’ve hit the limit of my shade-tree mechanic skills. Thank you all for the help.

If the temp swings are that erratic, maybe there is air trapped in the cooling system and it needs to be bled out.