Perplexing Overheating Problem

2063 Views 5 Replies 4 Participants Last post by mrk4art, Jul 5, 2010

mrk4art

Discussion Starter · Jul 4, 2010

Hello. I am new to the forum & have read numerous postings about overheating problems, but my issue seems it may be unique.

I recently purchased a 2000 P38 4.6 HSE (Bosch) with an overheating problem. I stumbled upon it at a very low price so I bought it because it's in beautiful condition, so I took a gamble.

It doesn't overheat at idle (temp gauge stays at dead center), but after driving it for about 15 minutes the temp gauge suddenly moves into the hot zone, red light comes on & coolant comes out of the overflow hose.

I installed a new thermostat & radiator. Also checked the compression ---it's fairly even; also did a cylinder leak test & tested the coolant recovery tank for gases using the bottle with the chemical that changes color. All of that came out normal. We also changed the coolant & purged the air out of it. The engine runs smooth, and there is no water in the oil or milky stuff on the inside of the oil filler cap. The fan's viscous clutch seems to be fine.

We had drained the coolant out in order to give it another flushing, then we refilled the cooling system with all water just to test the truck (so that we wouldn't waste more coolant in case we would have to pull the heads). With the system filled with water we again burped the system, then again test drove it to a gas station, shut off the engine to put gas in, drove it back to a repair shop. Seemed ok, so I drove it 10 minutes to home, but once I arrived it instantly overheated.

It doesn't seem to have any of the symptoms of a head gasket/head/block problem, so I don't know what to do. Is it possible that perhaps it just needed a good burping, which took care of the overheating problem, but now it overheats only because we have 100% water in the system for right now? The previous owner pulled the truck over as soon as he saw that it had overheated, btw.

You all seem to have a lot of experience & knowledge about this, so I'm hoping someone may have an idea. Thanks.

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kmagnuss

· #2 · Jul 4, 2010

The 100% water won't make a difference. That's what a lot of people here in FL do all year.

My guess is that it still has an air bubble in there. I'd just keep a couple gallons of distilled water with you at all times and when it spikes to the red just fill the overflow bottle back up. Oh, and take off the top hose and pour water directly into it, while on an incline.

Also... you could have a small leak somewhere that's letting air in, such as the heater core o-rings (check the carpet for dampness and smell) or the throttle body heater (look on the driver's side valve cover for caked on dried coolant).

Best of luck.

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paul.adshead

· #3 · Jul 5, 2010

I would suspect the water pump impeller is damaged/water passages slightly contstricted, causing insufficient water to be moved through the block/heads.

Also, the header tank cap could be faulty, venting at too low a pressure. My '97 4.6 has had this cap replaced.

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mrk4art

Discussion Starter · #4 · Jul 5, 2010

Thanks very much for your responses. We had removed the water pump & it looks new, the impeller is good & water chambers look good. There is no dampness or coolant odor in the footwell. There is no evidence of dried coolant on the driver's side valve cover, BUT there is evidence of dried coolant or mineral-type deposits all around that throttle body plate where it attaches to the underside of the intake (plenum) chamber. Could that be the culprit? I had already removed those two hoses a couple of days ago & blew through them to make sure they were clear.

Also, a couple days ago I jacked up the front end about 20 degrees to burp the system at over 2000 rpm --is it best to have the coolant recovery tank cap on or off when doing that?

Forgot to mention in my original post that the cooling system builds up quite a bit of pressure, to the point where the top radiator hose gets pretty hard. How hard is it supposed to become once the engine is warmed up?

Do you guys think it could be a cracked head or head gasket?

Thanks again.

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viperover

· #5 · Jul 5, 2010

I see you mentioned you replaced thermostat and radiator, was this is the same reason you are having now.

Did you clean out the AC condensor, the one in front of the radiator as that maybe partially blocked.

Your over heating issue after 15min is abit worrying and Im tending to lean towards blown head gasket.

Take note how fast the rad hose gets hard as that usually a good indicator of a blown gasket

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mrk4art

Discussion Starter · #6 · Jul 5, 2010

No, I have not checked the A/C condenser. I did not think that would have anything to do with the cooling system (How would the condenser be related to the cooling system?). Yes, I did replace the thermostat & radiator because of the current overheating problem.

You guys have any other suggestions?

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