Do I need a bigger radiator?

[pacman]

Hi Guy!

On my radiator (Volvo 440) i have a thermoswitch for the electric fan. It´s located in the center of the left radiator tank, beneath the inlet duct.
It´s set for 95 deg C, and i have tested it so i know it works.
On top of the head, between sparkplug 1 & 2 is the sensor for the engine water temp gauge. When running the engine the temp needle on the gauge rise until it reaches 82 C, where it stops. That´s normal becasue the thermostat opens at 82 C.
When cruising at normal speeds (90 km/h)the gauge reads 82 - 85 C. But when the speed drops to city speed (~50) the temp can soon rise to 100 - 110 C on the gauge. Problem is that the fan does not kick in automatically; i turn on the fan manually with a switch since i´m concerned about the engine temp. Only a couple of times have the thermoswitch turned on the fan.
The radiator is ducted from the front for better airflow. But still, if i have an intercooler in front of the radiator the temp will never stay at 85....

Do I need a bigger/better radiator? Why is it such a difference in temperatur between engine water and water in the inlet tank? I thought that if the water in the engine is 110 C it should at least be over 95 C in the rad inlet.


// Peter C

[Julian]

Out of curiosity have you checked the accuracy of the sender unit in the head?

I had a similar issue with my Explorer (tow car) that gradually became worse until I was convinced that the radiator was totally blocked while in reality the sender was slowly breaking down internally changing the output voltage unexpectedly.

To have a difference between the reading on the dial and the measured temperature in the radiator is not unusual, to have a big difference on the other hand is unusual. If the switch on the radiator is on the output side of the flow then the radiator is actually doing the job and that is the reason why the switch is not tripping automatically and that should answer your question by itself.

If however it is on the input side of the radiator and not tripping then it sounds like something else is wrong (referring back to the accuracy of the dial reading). Simple temperature strips allow you to see easily what the temperature is at both ends of the radiator.

You should only really need a different radiator if the fan is cutting in all the time automatically, that this isn't happening would suggest that everything is actually adequately specified.

If you are really concerned with the radiator I would make sure that the existing one is operating at full capacity first, it is not unusual for the core to block up with congealed debris that is very hard to shift. If this has happened you may find that a new standard radiator is fine, a heavy duty radiator is normally available as a replacement, generally for towing purposes. If you really need something more substantial then you can go for a purpose built aluminium core radiator but they are expensive and tend to be thicker (front to back) than standard so if space is an issue you may find there is little improvement as you are forced to go for reduced core count, in which case the only real saving is weight.

[Guy Croft]

Some good points by Julian, thanks.

The radiator is coping with the demand for heat rejection at high load when the vehicle is moving fast, as it should. It is - as we all know - normal for the heat dispersion from the rad to be insufficient at low speeds - because the airstream thru the matrix is too slow to be effective - and thus a cooling fan is needed. This is not a rad capacity problem.

We know the fan is not cutting in as it should. This is the fundamental problem. We know the thermostat is open sufficiently to allow high coolant flow. Thus, if the relative temperatures are indeed as you state (Julian refers to the need to check them first to ensure it's not simply a gauge issue), then I suggest that the cause of the engine overheating at low speeds is one of these:

1. Defective fan control switch - or relay/wiring
2. Debris in the radiator preventing the sender from seeing the true lower-end coolant temperature in the rad (I think the fan sender switch is always located in the lower radiator section - if they were located at the top they'd be on all the time)
3. Worn or slipping water pump impeller. Rare, but I have seen it. Drive belt likewise.

Note that, if the radiator air passages were blocked, or the coolant ones for that matter, the temperature of the rad would encourage the fan to come on. It's not. so I figure the problem lies with the fan.

GC

[Kev Rooney]

With 15 years experience in the radiator trade I woudl say the problem is almost certainly a silted rad, especially around the fan switch. The crossflow radiator design is flawed in this respect especially if run with an inadequate antifreeze ( anti corrosion ) mix. I would take it to a good rad shop for a flowtest as they are equipped with the special high volume/flow standpipes which cannot be recreated at home.

[Guy Croft]

Kev, hi

yes, quite so. You worked for Serck (if my memory serves me correctly), did you not?

GC

[Kev Rooney]

Indeed I did Guy, well remembered ..it was along time ago. However I still visit my old branch and keep in touch with current technology.