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Car overheating

My car overheats after about 10 miles. No leaks, no steam in the radiator, no white exhaust and oil is not milky. Radiator overflow is dirty. Thermostat was replaced and radiator flushed in May '09. Since that time we have been able to drive 15-30 miles without any overheating. Past weekend started overheating within 10 minutes. Took it to an independent shop, replaced radiator cap, a sensor and a switch. He thought problem might be water pump. Advised taking it to a dealer. Dealer wants to troubleshoot, new radiator, Nissan thermostat, top engine decarbon, replace spark plugs,new water pump. Cost 2K. Car has 140K miles, I am not replacing all of these parts without knowing they are damaged. Have called another independent mechanic who says he can test parts to see if they need replacing. Money is very tight, please advise.

What year Nissan is it? 140k is not a lot of miles, but age might be a factor. I think that you have made a good choice going to another independent mechanic. Rocketman

It is a 2001 Nissan Maxima. Thanks for your reply.

The “top engine decarbon” is a waste of your money and will do nothing to cure overheating. You may or may not need new spark plugs, but they also have zero effect on overheating.

What do you think the chances are that the replaced thermostat was faulty, and do you recommend only Nissan replacement parts. The thermostat that was replaced in May '09 was not a Nissan product. I may need a new thermostat, radiator, or water pump. Thanks

Go to the guy who says he can test the parts to determine if they’re bad before replacing them. He’s the one that’s doing the job properly.

Water pump flow can be tested. The radiator can be “tested” by mapping it with a pyrometer. Cool spots and hotspots indicate internal blockages. There is absolutely no need that the T-stat be Nissan and yes, it can be tested with a hotplate, a thermometer (he’ll probabbly use a thermocouple and meter} and a Pyrex vessel.

There are other possibilities such as a failed radiator hose lining, but I have no doubt he’ll check for this. People who diagnose do these things.

The top engine decarbon will do nothing for you. And while the spark plugs might be overdue, they’re not related to the current problem.

My wild guess is that you’ll need a radiator. But I would not change it without verifying the need, and I’d get an aftermarket one…for about 1/4 to 1/3 what the dealer would charge…just for the part.

Post back with how you make out. We care.

It has also been suggested that it could be a cracked head gasket. Is there a test to determine if that is the cause of the overheating problem. Thanks so much.

Yes, there is. More than one, actually.

Perhaps the best is called a pressure leakdown test. A pressure gage with an attached shutoff valve and air input valve is inserted into the sparkplug holes. The crank is manually turned until both valves are closed and the cylinder is pressurized with air. It’s then monitored to see if it loses pressure.

Coolant can also be checked for the presence of combustion gasses.

Also, bubbles coming out the radiator cap hole when the engine is running is a bad sign. They’ll be combustion gasses pushed through the headgasket breech and into the water jacket, migrating up out the radiator fill hole.

As you’ve already noted, milky oil, white smoke (which is actually coolant that’s been drawn into the cylinder and vaporized) are also signs.

The Nissan is at the shop today, just spoke with the service manager and hearing the symptoms he thinks it may be the water pump. It will be upwards of 500 for the serpentine belt, water pump and labor. Says he can’t be 100% sure though. Can it be determined before replacing if it is the water pump? They haven’t had time to look at it, he is just hearing the symptoms and guessing right now. He says since its not overheating on idle and I drove 30 miles to get it to the shop with no overheating at all, that may be an indication of a “lazy water pump”. Thanks.