Overheating Issues?

[TeamSid]

I bought my 2.1DJ Caravelle about 2 years ago with what I was told was a problem with a dodgy temp. sensor/guage (always climbing into the max with the LED flashing once the engine had warmed up) That was until yesterday when I carried out a couple of electrical tests with help from the Wiki section and found out that everything is working correctly and my problem is actually an overheating issue. The 2 pipes/hoses which lead to the radiator are barely hot but when bleeding the system I am able to get water through the bleed screw, albeit not very hot. Could it be due to the thermostat not opening fully, or a blockage in the system, and have I been driving around for the last 3 thousand miles with the engine temp dangerously high? I'm going to take the 'stat out when I get a minute to check. Any ideas? Cheers.

[tetleysid]

Friday 13th ... spooky eh? Anyways do you have any water leaks any where? If you have water dripping ... even a small amount ... around the engine block then it could be failed water jacket gaskets ......... see my little (little!!) resto.

[TeamSid]

Hi TetleySid. No there's no water leaks anywhere. I was fortunate enough to inherit a genuine VW exchange with the van, which has covered 35K miles so I'm hoping everything is still in tiptop condition. I'm about to go and have a poke around so I'll give an update soon. By the way, I really enjoyed reading over your resto. We're big fans of France and were extremely jelous after watching your videos. We're planning going back to France this year to Sarlat then over to the Charante to see friends.

[TeamSid]

Well, I've just removed the thermostat, stuck it in the fridge to ensure it is definitely closed then put it in the wife's coffee cup with freshly boiled water. Result.....nothing! No movement whatsoever. I'll try and get a new one tomorrow and give it a try. (must remember to give the cup a quick rinse.....or will I)

[TeamSid]

I've just retested the thermostat in a pan of boiling water and it opens, but only when the water is really boiling. As soon as you turn off the heat the 'stat closes again. I'm not sure if this is correct or not. What do you reckon ? The van's done nearly 200K miles and it could well be the original unit so could it be getting a little tired?

[TeamSid]

Well, I've decided that the thermostat is OK so I've refitted it and bled the system, following the Haynes manual method. Water eventually reached the bleed screw so I took that as a success. I let the engine warm up, again into the max and the radiator is stone cold. Any advice, please?

[AdrianC]

I'm not sure if this is correct or not. What do you reckon ?

...that a thermostat is cheap enough that it's daft to even take the chance. Replace it.

It's one thing that I usually replace as a matter of course on any older vehicle that I buy, anyway. They're usually long-neglected, and a bloody good service not only helps the vehicle itself, but it helps me get my head around how it's put together, and helps me spot any other potential problems.

If the engine's roasty-toasty, but the rad's cold then water clearly isn't reaching it. That's gotta be either a blocked pipe somewhere along the line, a blocked rad itself (assuming you've checked the rad all over for temp, not just in one spot), or a dead 'stat.

[pauly8888]

Well, I've decided that the thermostat is OK so I've refitted it and bled the system, following the Haynes manual method. Water eventually reached the bleed screw so I took that as a success. I let the engine warm up, again into the max and the radiator is stone cold. Any advice, please?

The theory is:
water bubbles and boils (in a pan on a stove) at 100 Centigrade;
water under pressure boils at a higher temperature;
your thermostat should be opening at about 87 Centigrade;
you need to use a thermometer to test the temperature of your missus' cuppa.

[kevtherev]

I have to agree remove the possibilities by replacing the stat.. cheap as chips
It should start to open at 87 deg.

[TeamSid]

Cheers folks for all your comments. I think I'll get a new thermostat and flush out the system. The van's had a new radiator at some point and I've noticed that the flow and return pipes are both located on the underside of the radiator next to each other. If the flow and return pipe are connected the wrong way round, would that have any effect? Also, is the thermostat on the return side of the system? Thanks again.

[Ian Hulley]

Perhaps be an idea to buy a Haynes

Ian

[kevtherev]

Agreed

The thermostat is on the return side... like ALL VW engines it opens to allow cooled coolant to enter the engine.

[TeamSid]

Well, before spending my £9 on a new thermostat I tried one more time at bleeding the system through, and this time with success. A mechanic friend suggested raising the back of the the van and bleeding it that way. I'm not sure it if helped but it did appear to vent out alot of air into the expansion tank. The radiator's now hot, the first time since God know's when, but the temperature is still climbing into the max. Time to switch back to the electrical section of the forum. Many thanks for all advice.