cooling mystery

[Don 130]

My '97 300TDI has developed a problem with the cooling system. I had a look last night at other peoples issues to try and find a similar set of circumstances, but nothing seems to match up. The head gasket was replaced in march 2010. In August the truck started overheating. I replaced the pressure cap and thermostat but still it continued. The mechanic had it while I was getting a new knee fitted. He said he'd pressure tested it and everthing was ok. He tightened down the headand sent it home. That was about the end of August, and it's sat here sinc then untill i could drive again. In the last few days I've done some very short trips around the neighbourhood and all seemed well untill yesterday when it got hot again. I couldn't see where the water got out, but it was low. I topped it up, checked it was bled ind on using it again today it overheated in about 10 mins of driving. It seems to be pressurising the water jacket somehow. I thought of the headgasket again, but the mechanic reckons that would have shown up in the pressure test. So, what other things could cause the pressurisation?. Sorry for the long winded story, I'd appreciate any suggestions.
Don

[87County]

The cause may be partial radiator blockage.

I have had similar symptoms and they were resolved by having the radiator "rodded" (tubes cleaned out with the tank removed) and hoses including the Y piece ejector replaced.

Radiator work will hopefully only cost $100 - $120 if you take it out and take it into the shop.

HTH :)

[wrinklearthur]

Hi Don


Is the exhaust is blowing moisture ? it would be a cracked head.

How is the oil, is it going milky ? then its a blown head gasket.

Look under the radiator for signs of coolant, cracked tank? repair.

Water pump noisy and leaking ? replace with new pump

Look under the front floor mat is it wet ? the heater core needs replacing.

Check for cracks or pin holes in the hoses ? replacement of all hoses.

Is the 'P' gasket weeping ? the cheapest fix of the lot - a new $4.00 gasket and an hours work.

Good luck and Cheers Arthur

[Don 130]

wrinklearthur,
Thanks,I've checked all those except for the moist exhaust. There's no leak apparent anywhere. the pressure builds up and the water blows out through the pressure cap, and the oil is suitably black.
Don.

[wrinklearthur]

wrinklearthur, thanks,I've checked all those except for the moist exhaust. There's no leak apparent anywhere. the pressure builds up and the water blows out through the pressure cap, and the oil is suitably black.
Don.
Hi Don

Good for that.

Now, to check for the coolant flow is a bit tricky, but it can be done.

Water flows into the radiator at the top, after the thermostat opens, so the motor must be at operating temperature for the following test.

Run the motor up to a fast rev, then with your hand, protected by a glove or similar, compress the top hose and note the effort required to compress the hose, then repeat for the bottom hose.

If the bottom hose feel like it has a lot less pressure in it, then the flow through the radiator is impaired.

Also, if the bottom hose almost flattens, when the motor is revved up fast that is a sure sign that the water pump is trying to do it's job, but the restriction is too great.

Without a sufficient flow, the motor can't dissipate its heat build up and as the coolant expands, it is forced out.

Holding a container of chilled water just away from the end of the exhaust will soon show, if there is too much moisture present in the exhaust gas.

Cheers Arthur

[Don 130]

wrinklearthur and 87 County,
Thanks again, The mechanic rang this morning to say he's pressure tested it again and it held rock solid, so the radiator is the next suspect. I'll go out there on Monday to pull it out, but do the moisture test and flow test first.
Don

[dullbird]

I would also taken out your thermostat and check it it is working...dont think just because you bought a new one that it is working OK..

We had huge cooling problem with our 90 once and it went on and on and on..we had changed the thermo twice because everything else was working and low and behold it was again a faulty thermo stat.

I also believe anyway that once you have over heated a car they should be changed out regardless.

[onesilop]

sorry for the late bump, but did you ever find the issue?

I am having similar problems and the Mechanic is simmarly mystified.

[mudder110]

had the same thing on my 98 110 tdi my radiator was stuffed never realy
got into the red but did get hoter then normal.
my old girl (defender) had 280000ks when she needed new radiator spent the extra to get a extra cooling row on radiator have you checked the cooling system is bleed corectly thermostat needs to be fully open to be bleed properly or you can get back presure if the temp drops when you open the heater radiator is blocked good luck

[nedflanders]

If the heater matrix hoses are getting hot the water pump is probably OK, what about viscous coupling, is it locking up OK? As previously stated has the system been bled?