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Truck radiator runs dry all the time

I have a 1990 Toyota pick up and, even though I have had the radiator removed and tested twice for leaks, I still loose fluid. I drive 30 miles - after having filled the radiator to the top - and then find it empty. The overflow radiator fluid bottle is always full to the top but the radiator will not stay full. My radiator man has told me to place a large piece of cardboard under the car to see if there are any leaks - there are non. Please help, I pay more in coolant than I do in fuel!

Hi Grannyannie,

There are two other places coolant can go, and both are much more expensive than replacing the radiator or hoses. It might be going into your oil, or it might be going out your tailpipe. Both problems have the same solution; a head gasket.

If it’s the oil, it’s very easy to check. Just pull the dipstick. But you need to get it over to your mechanic PRONTO!!

There are other places that can leak coolant such as the hoses or water pump weep hole. The water pump will only leak when the engine is running. So I guess I’d fill the radiator again and let it run and take a look all around the hoses and water pump for a fluid leak.

Or get someone to do a pressure test on your system, that is, with radiator in place. Your mechanic should have done that. Did he?

Agree with Western Roadtripper - why are they removing your radiator for testing ? They should do the pressure test in place and with losing that much coolant it should show them where it is going.
It can go into the transmission too.

Agree a complete cooling system pressure test will locate where the coolant might be going. If there are no external leaks, there will be an internal leak, most likey througgh the head gasket into the engine or somewhere else.

In any case an engine compression test is strongly recommended if no external leaks are found’

I had a hairline crack in a cyclinder. Took 3-7 days for the coolent level get low enough for the temp guage/lite to turn on. Oil was clean, no leaks in hoses. Radiator held pressure. No unusual tailpipe smoke (normal morning vapors). Discovered by pressure test.


There are two simple things you can do easily which will help troubleshoot this problem.

  1. Pull out your oil dipstick and look carefully at the liquid on it. Note if it looks like oil, or if it’s different, maybe milky brown or something like that, or anything out of the ordinary. You might want to let some oil drip into a clear container to examine it. A bottle cap which is white will do well enough. Oil can look brownish while sort of clear, you’re probably familiar with that. If it’s been in there a long time, it may be nearly black. Either of those are fine. But a foamy, frothy look will be an important clue. And is the level more or less normal? Or is it overfull?

2). If you have an automatic transmission, do the same with the transmission dipstick. Does the fluid look pinkish or reddish, or something else? As Oldtimer 11 wrote, a cooling system leak can allow mixing of automatic transmission fluid and coolant. That’s because transmission fluid has a line running to the radiator to cool the fluid. It’s supposed to be a separate system, but leaks are possible. If this were the case, it would be less bad than a problem in the engine itself. Again, how about the level, normal or overfull?

Please report what you find in both. And whatever you do, don’t drive without coolant or you’ll definitely make your problem much more expensive to fix.

BTW, your mechanic’s choice to remove your radiator twice raises doubts about his competency. A proper pressure test with the radiator in place would take maybe ten minutes, and would probably have answered the questions right away. His advice about the cardboard under the truck is dubious. Most leaks appear occur only when the engine is running and hot and the system pressurized. I had a leak that I couldn’t locate even with a hot engine. The pressure test showed it easily. So I suggest that you try someone else. Actually it’s a simple and non-technical test, one you could do yourself if you could borrow the tool from an auto parts store lending service, Autozone for example.

If your overflow tank is full to the top, use a turkey baster to remove half of it’s contents. Fill the radiator and drive the truck. Let it cool overnight. If the tank is full again and the radiator is down, you have a blown head gasket…This assumes your are using the correct radiator cap and the cap is in serviceable condition. Most modern shops have a simple tester to verify blown head gaskets…