Why would radiator need to be replaced?

With problems like these with no clear cause, it is up to the mechanic to figure out where to start with the diagnosis, and no two people will approach it the same way. In this case, however, it seems like you are correct that things were overlooked. There is a potential cause for that too. Mechanics are real good at communicating with other mechanics, as they speak their own language, but they are real poor at communicating with customers. That's why there's a service writer in the middle to translate. There are going to be a lot of things the mechanic checked that never get documented on the repair order, and that's all the service writer has to go on. The mechanic will document what he finds wrong, not what he finds right, . . . usually.

Everything you listed could be discounted as not the cause of the low heat, but that's easy to say when you aren't right there in front of the car. If the impeller was cracked and slipping, which WAS a real common problem on VWs a few years ago, the engine should have a tendency to overheat, especially at higher engine speeds. Since it's not doing that, the most common suspect would be a thermostat that isn't closing fully. The clue is the radiator and heater hoses will all be cool. Normally they should be too hot to hold onto for very long. A plugged radiator will cause engine overheating too, and you would get real hot air from the heater.

Keep in mind too that Audis, VWs, and BMWs are very expensive to repair. Parts are very expensive and many mechanics won't even work on them.

Thank you for the information. I will talk with the mechanic about elementary troubleshooting measures that may have actually been performed.

Could you comment on what condition might warrant radiator replacement in the absence of leaking or overheating? I have searched for an answer to this but can't find anything. Everything I've read suggests that flushing should fix a plugged radiator...

Also as follow up, I did take the car to an Audi certified shop. My concern with the prices being charged for parts is that I've looked at several on-line stores including BuyAutoParts.com, and found new, guaranteed OEM parts, in stock and ready to ship, for an average of 60 - 70% less.

Sorry for the delay. I'm doing battle with a stubborn computer.

The radiator's job is to provide as much surface area as possible so the air can remove the heat from the coolant. That amount of heat varies all the time and every radiator is selected to meet the most extreme conditions and more. Its ability to disperse heat far exceeds the engine's needs. That's where the thermostat comes in. Without it, the heat would be given up much too quickly. You would notice cool air from the heater. The engine would experience excessive wear from parts that don't fit properly until they warm up and expand, and from sludge in the oil from fumes that don't vaporize and burn off.

The thermostat slows the flow of coolant to the radiator until it reaches the desired temperature, so while the radiator CAN cause overheating by failing to disperse the heat, it is supposed to be effective enough to cause low heat. When you have an engine temperature that is too low, don't look at the radiator; it's working.

As far as the radiator being plugged, with the better additives today in antifreeze, that isn't too much of a problem. If some of the tubes become blocked, you'll be able to run your hand across it and feel hot and cold areas. The engine usually won't overheat all of a sudden. You'll see the temperature gauge go up a little higher over a period of weeks each time you drive the car. The biggest problems with plugged radiators are with GM vehicles with the miserable Dex-Cool, (Dex-Mud) antifreeze. To avoid problems with those, you have to change the coolant a lot more often than GM recommends.

A more common reason to replace the radiator is when it doesn't give up the heat fast enough. That is caused by corroded cooling fins. The same thing will happen if you have a butterfly collection stored in the fins, but that can be blown out. When the cooling fins are corroded, they will crumble like a rotten chocolate chip cookie when you rub your fingers over them. This too doesn't happen suddenly. When it occurred on my '88 Grand Caravan, it had been driven in Wisconsin snow and road salt for 14 years. The temperature gauge stayed in the normal area in the winter, but in the summer, on a road trip to Colorado, the gauge started to creep up if I was going over 60 mph and it was over 60 degrees outside. That went on for a year, and the clue was that the temperature went back down in slow city driving when air flow is reduced and the problem should get worse. Also, turning on the front or rear heater brought the temperature down because both heater cores are miniature radiators. Eventually the running hotter than normal occurred when the outside temperature was as low as 30 degrees or running at lower speeds. I procrastinated as long as possible until holes started appearing in the cooling tubes. I patched at least a half dozen holes over about two months, then finally gave up and replaced the entire radiator. This one is 11 years old, and the van is still my daily driver, rust and all. There's probably not another dozen like it left in the state. (I'm watching for a rust-free one from down south).

As for those parts you found on the internet, don't be too hard on your dealer. Food costs a lot less in a grocery store than in a restaurant. The dealer, or any repair shop for that matter, has a lot more costs involved in ordering and stocking parts. Ordering parts online is typically only done when you're going to install them yourself. Just as you wouldn't bring your own food to a restaurant and ask them to cook it for you, shops don't like to install customer-supplied parts. It is somewhat common to find a new part is defective or damaged in shipping. When the shop supplies the part, it is their responsibility to get that part replaced at no charge to you. That is one of those additional costs involved in getting the part for you. When a part you supply is defective, or the wrong part, you have to get it replaced. That could mean your car is tied up for days or weeks. The mechanic has to get it out of the shop during that time so they can work on other stuff.

Also, believe it or not, we break new parts sometimes. When that doesn't happen on a regular basis, the shop owner will be rather forgiving of his mechanic, and the parts department will get a replacement. They can't bill you for that second part, and it's not the fault of the auto parts store or supplier, so paying for the broken part is another one of those costs associated with selling parts. A better way to think of it is to look at all the costs and government regulations that go into providing a meal at the restaurant, and compare that to cooking the same meal at home. You can see the cost at home is a lot higher than just for the cost of the food.

I use the Rock Auto web site many times each day for reference. Many people have told me they have great prices, but whenever I've looked up things I'm familiar with after working for a very nice dealership for ten years, their prices are right in line with the other auto parts stores in my city. I've shopped at Auto Zone, Carquest, Advanced, and most often now at O'Reilley's. I just bought a new ball joint for my van and the "cheap" one cost more than when I worked at the dealership. When you add shipping, the better deal is at the local stores, and it's easier to return if it's the wrong part.

To get more specific about your car, your engine is of the "interference" design which means if the timing belt breaks, the pistons will hit and bend the open valves as they coast to a stop. That is a very expensive repair bill. All manufacturers specify the recommended mileage intervals the timing belt should be replaced before it breaks and causes that damage. Your water pump is driven off the backside of the timing belt. When a mechanic has your best interest at heart, which most of them do, they will strongly recommend replacing the water pump at the same time. That is relatively cheap insurance. The pump is just as old as the rest of the parts, and it is one of the idler pulleys for the timing belt. If the bearings go out in the pump, it usually causes the timing belt to shred, and there's that valve damage.

To turn it around, it's a lot of work to get to the timing belt, and just as much work to get to the water pump, so it is customary to replace both at the same time. Along with the timing belt, it is customary to replace any tensioning devices too to insure the quality of the repair. That is one of the parts you listed. To not replace it is like buying a whole new outfit and wearing old socks. You could, . . . but you wouldn't.

As a point of interest, Rock Auto makes the unusual point of specifying the replacement water pump has a metal impeller. That means the original one had that plastic impeller that has a known high failure rate. Your mechanic was on the right track when he observed the engine temperature was a lot higher than the radiator temperature. That could be caused by poor circulation from the impeller slipping and not moving the hot coolant to the radiator and the heater core. That doesn't agree though with his diagnosis of a plugged radiator. If it was plugged, it would still be cool, but the air from the heater would be unusually hot.

You asked for my thoughts on repairing a car you just paid off. Think of the repair bill as a couple more car payments. The alternative is to trade the car and start all over with car payments. Also, the newer the car, the more unnecessary computers it's going to have in systems that never needed them before. The lack of those computers is why I'm looking for another '88 minivan.

I wanted to add one last comment about you not expecting such a big repair bill. It is common for car owners, myself included, to not be aware of things happening underneath, but it's those things the mechanics look for. Just because a hose isn't leaking yet doesn't mean it isn't dry-rotted and cracking. Tire wear patterns can indicate an alignment problem when there are no other symptoms. Low brake fluid level usually means it's time for a brake system inspection, and probably new front brake pads. Things like these are checked during routine services like oil changes, and that's when you're hit with the recommendations you weren't expecting. If you never go to a doctor, you're either in very good health, or you are blissfully unaware of your cholesterol level and risk for other ailments. When a car hasn't been seen by a mechanic in a long time, there will usually be things they spot that should be attended to before there's a catastrophic failure on the highway. I used to see that all the time at the dealership. We had a lot of do-it-yourselfers who did real good work but knew when to see a professional. Those are the cars on which we often pointed out things that needed attention, then we let the owners decide what they wanted to do.

Finally, I have to point out that patching my leaking radiator is not the way we repair our customers' cars. Our goal is to fix your car once and to do it right. My goal for my can was to save money. I wasted dozens of hours trying to keep alive a radiator I knew was going to die soon anyway. If I am left stranded on the side of the highway because I was cheap, I have only me to blame. If YOU'RE left stranded because I tried to save you a few bucks, I'M the one you're angry with. I'll risk my van; but not your car.

Wow, thank you very much for your indepth response. I am all about the "why" (probably to a fault), and you provided thorough and clear explanations to each of my concerns.

I feel much more comfortable with the whole picture of what is going on with my car now, including associated costs. I'm also happy to have a better understanding of how the vehicle operates. I am a registered nurse, and it is interesting to find that the roles of various auto parts' function parallels different body systems in many ways, as does the importance of preventative maintenance!

I appreciate the time and knowledge that you clearly put forth, and will most definitely come back for more advise in the future!