Thread: Random Overheating

Originally Posted by Red90

Well you want to fix the issue. When not loaded it should sit at around 82. If it is the thermostat, you should get a new one. If it is the gauge, you need to fix the wiring. Bad wiring may prevent it from showing when it overheats.

My D1 Tdi will happily sit on anything between 82 and 90 degrees, depending on the ambient temperature, load, gradient, wind (head, cross or tailwinds all have differing effects), even closely following other vehicles can make a few degrees difference.
I only start to get concerned if it hits 95 and over, usually a simple adjustment to the throttle foot will bring egts and subsequently temps, down again.
As Trout said, the thermostat does not set the operating temperature of the engine, only the point at which the coolant gets circulated through the radiator.

Not sure how Countys are wired, but one thing that can cause higher readings or spikes is a bad earth to the panel the gauge is sitting in or a bad earth to the gauge itself.

Had this issue with an XW wagon with a 302 years ago. Gauge always read high........ had a triple core rad made at great expense, no change. Thermo opened on the stove at 82.

Couple of years later a globe blew in the dash and I brushed the main earth wire while replacing said globe. Temp now normal, so I just tightened the screw or nut holding the earth onto the panel and it was all fine ever after.

cheers, DL

Originally Posted by donh54

My D1 Tdi will happily sit on anything between 82 and 90 degrees, depending on the ambient temperature, load, gradient, wind (head, cross or tailwinds all have differing effects), even closely following other vehicles can make a few degrees difference.
I only start to get concerned if it hits 95 and over, usually a simple adjustment to the throttle foot will bring egts and subsequently temps, down again.
As Trout said, the thermostat does not set the operating temperature of the engine, only the point at which the coolant gets circulated through the radiator.

A TDI should have an 88 C thermostat and will run up to 95 as that is when the viscous unit on the fan locks up. If it goes below 88, the thermostat is leaking.

On a 4BD1 with a fixed fan, it should sit solidly at 82 C until it is pushed so hard that it runs out of cooling capacity. This should be a very rare thing.

The OP has a specific problem. It is always showing above 90 C, even when not driven hard, so there is a problem that should be addressed. As above, a high reading gauge can be caused by a ground side wiring issue. It is critical to get it properly solved as it is easy to have an overheat occur and not know about it, when there is a bad wiring connection.

Buy a cheap infrared gun. The hand is good for telling the difference ie wheel bearings, but not for quantifying. Also good for when the fridge is suspect or not set correctly.

More than likely the wiring.

I thought thermostats were designed to provide variation in opening - not just a case of either fully shut or fully open. Your vehicle is at operational temperature on the flat but on steep hills or extra load the temperature rises slightly beyond, so the thermostat uses its reserve of opening capacity to allow further increase in flow?

My experience with them is that there is a weep hole that allows flow independent of the thermostat, I assume to allow pressure relief for the water warming on one side? That the hole has to be set to the top of the housing when installed.

No thermostat can result in excess water flow pulling hoses closed, increased temperature reading, until vapour pressure from the heat opens the hoses again and normal temp returns for a while.

I blew a radiator bypass hose and didn't know about it. The OEM gauge showed high but not hot, checked the expansion tank but it was always full of course.
Lucky it was winter time and I was driving at night, I did four 160km trips with it like this, before pulling the motor out to fit turbo and finding this problem!
Since then I have fitted a VDO gauge but not sure if I have the right sender for it, and a recond V8 radiator.
It normally sits at around 85deg but going up the few good hills I have around here it goes up to 105deg, it doesn't seem to get any hotter than this, but i drive to the EGT keeping a max of 700 when towing and loaded up. (12PSI)
I think I have found the VDO sender a few days ago, so about to change that over to see any difference.

The VDO sender you want is part number 323-417 (M16x1.5)