QuestionQUESTION: When running the van with the A/C on at times will run fine and the temp gauge will stay in the middle and at times it will spike to the max. When the temp gauge is normal and I stop and shut the van off it will boil over and dump coolant. The after-run fan doesn't kick on when the van is shut off and only the driver side fan comes on when the van is running with the A/C on. If I run the heater full blast before shutting down sometimes I can get it to not dump coolant. I've checked the top radiator hose for pressure after shutting down the van when its to temp and there is no firmness to the hose and I can take the radiator cap off with no pressure on it. There is no coolant in my oil or oil in my coolant. Where do I start?
ANSWER: Hi Paul,
Some of your expectations for the fan performance may be in error but let us start with the soft hose and boiling over after shut down. That might indicate a thermostat that is failing to open when it should (start to open at 192 to 199, be fully open at 220). Also, it may be that because of this when you start the van later you have lost coolant and so have air instead of coolant in the upper most part of the system (the top hose). So the least expensive fix to begin would be to replace the thermostat, or at least remove it and test it in boiling water.
Another possibility is that either due to air trapped in the upper part of the system or to loss of accuracy that the engine coolant temp sensor is not properly telling the engine controller what the temperature of the coolant is and so the fans will not be activated until the temperature is above the proper level. So replacing the coolant temp sensor would be something to consider. You could measure the resistance across its terminals by removing the plug on its top, and you should observe that when cold it should read 10,000 - 14,000 ohms and as the engine warms to operating temp (about mid-scale of the gauge) the resistance should drop down to between 700 and 1,000 ohms. If it doesn't then if you are sure that the system was full before the engine was started, that would be a basis to replace the sensor. It is located next to the thermostat housing which is where the top hose connects to the engine.
The fans are calibrated to come into play progressively based on the reading of the temp sensor and also based on the output pressure of the a/c compressor, so if the temp sensor was incorrect or there was less than a full charge in the a/c system you might well not see the high speed fan come into play soon enough. That high speed fan comes into play with gradually increased speed depending upon the temp and the a/c pressure at the moment.
You might also check that the manifold cans on each side of the radiator are equally warm when the engine is up to temp for if they were not that would indicate a partial obstruction of the coolant flow through the radiator.
So consider these observations/tests and possible remediations and let me know of your progress.
Roland
---------- FOLLOW-UP ----------
QUESTION: Thanks for the initial reply. I forgot to mention that I already replaced the thermostat before posting the first time. Since your reply I got a new temp sensor, removed the old one, tested them side by side in a pot of water upto boiling and they were both reading the same. No matter how hot the engine gets it won't pressurize. With the cap on I can squeeze the hot upper radiator hose with no resistance. I pressure tested the cap and the system. The system lost 1.5 psi over 5 minutes and the cap would blow at 16 psi and drop to 11-12 psi and hold. After the pressure test on the engine the fluid level dropped with no visible leak or hissing during the test. What do you think?
AnswerI am wondering whether squeezing on the hose is a meaningful test of whether the cooling system is pressurizing. Of course, the other point is that it won't pressurize significantly unless it gets near the boiling point of the coolant. It clearly must clearly pressurize when it blows off coolant. So go back to the beginning and go through the various scenarios that happen when you drive for short vs long distances and for the ambinent temperature's effect on behavior. I am not clear what is the specific problem.
Roland
