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4 Cylinder Hot Engine - Causes/Answers

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Hi Folks,

Many thanks to Menno for starting this.

these replies have been contributed by members and will be added to for your help.

Please post your ideas on a separate post and I will transfer them - Roger


1. Grill: use an original shaped grill. Later, aftermarket grills have smaller holes. Up to 20 - 25 % smaller.

When in doubt, remove the complete grill for a while and see what happens. (Great suggestion by Don H.)


2. The cardboard air duct is a MUST! In essence the wide mouth grill is a design flaw when it comes to cooling

Without the air duct, too much air will pass the radiator on all sides without being funneled through the radiator.


3. Without saying: the radiator has to be in good condition.


4. Ditch the starter hole in the middle of the radiator. Have the radiator re-cored without the hole (+20% more cooling effect).

Perhaps an 'originality feature' and you will loose points on concours day. But these cars are made for driving, not for their beauty.


5. Use the original pressure cap (4 lbs, I think) 1 inch (25.4mm) is the correct projection.


6. Install an overflow bottle: the tube next to the radiator cap can be routed into the overflow bottle. Special rad cap required.

And there are more sophisticated systems pictured on the forum.


7. Don't overfill the radiator: when cold, with the cap removed, the fluid is about 1 - 1.5 inch under the neck


8. Use proper coolant. Blucol, Halfords Silicate etc etc But NOT OAT (usually pink)


9. Hoses from and to the radiator: make sure that these are fine condition. When in doubt, replace them. No need for fancy silicon hoses.


10. The attachment of the radiator filling neck and housing is vulnerable for cracks. Make sure it doesn't leak. And don't lean on the neck

when inspecting the engine bay.


11. Cam timing must be spot on.

12. Fuel mixture too weak and it will run hot

13. Water ways in the block must be clean, especially around cyl 4 and the drain plug.

14. A rich mixture may increase the temp.

15. Modern (Ethanol) fuel will increase the temp

16. Get rid of any air lock in the system particularly after filling. Fill with water open heater get engine hot with filler cap off ,

watch the gauge pump the hoses and wait for gurgle.

17, area between the radiator and the front of the engine:

the original fan is hardly up to the job. Has to do with the 4 blade design and the rake (is that the word here) of the blades:

very flat. Often, the fan is replaced with an aftermarket electric fan.

18. When removing the fan, be aware of the fact that you need to change the front end of the shaft *need input here, what to replace*

19. An aftermarket fan can be found on a scrapyard. You can also opt for a Kenlowe, Pacet or Revotec fan.

Be aware that there are 'pullers' (pulling air through the radiator) or 'pushers' (need to be mounted in front of the radiator.

Some fans can be altered from puller to pusher (and vv) by switching the leads.

20. Consider a proper mounting bracket for the fan. The 'through the rad' pins are known to destroy the core of the radiator...

20.1: Get a 8 blade fan from a TR6 (The Roadster Factory part #308353)

21. Connecting the thermoswitch can be done with inserting a probe in the upper hose (Kenlowe) or a special connector in the hockey

stick shaped downpipe of the cooling system. *The temp of the thermoswitch suited for the TR can be discussed here...*

NOTE -My Kenlowe just has the thermal sensor bulb wired to the header tank, in the 'corner' between the lower edge of the

tank and the cores. Seems to work fine.

22. best thing i did was to fit standard 82deg waxstat and fit a restrictor in the bypass hose warms up quicker and stays cool even with

standard fan been done to death on this forum already..

23. Cam condition/correct valve lift as a factor in addition to cam timing may/will raise the temp - slow process but worth a look.

24. Only thing I have not seen mentioned is the benefit of a proper 6-blade tropical fan.

25. TR4 Original grill, spot it a mile away. Every fin/ vane has a end cut out which allows you to BEND the vane to increase or reduce the

airflow. Needs care !

26. TR4 -Air duct is a must, however, the 2 inch gap either side benefits from being closed up also, easy to do

27, Heat soak: Big Iron lump. If you have an electric fan with an overide, switch it on when you hit traffic,

easier to avoid the overheat that triggers the thermo switch than to drag the temp down afterwards

28. Are you basing the temperature on indicated temp of the cars gauge and sender. Or actual temp via a known accurate system ?

How about the use of water wetters ? As these also have useful inhibitors


29. Retarded spark timing will cause hotter running. If the vac advnace capsule isnt working correctly to advance the spark at cruise, then that would lead to retarded running.


30. If not using an original bellows thermostat the bypass hose will need sleeving down by inserting a short piece of smaller bore hose.

This prevents too much of the water flow bypassing the radiator. The original bellows stat took care of this by restricting flow though

the bypass hose as it opens. A standard modern thermostat simply opens. The water simply follows the path of least resistance

and quite a lot will return via the bypass hose without being cooled


31. Cheap **** water pumps,too bigger gap between impeller and body,OK running round,not efficient at higher revs,or even an original

pump can cavitation if impeller set wrongly,worth checking?.

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Edited by RogerH
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