Ecuadorean Javelin in trouble

[Keith Clements]

I own a Jowett Javelin 1951, which I'm fixing to use it for Classic Cars Regularity Races. The engine is almost done, but we are having some temperature issues: the engine is working well, the temperature reachs 85°C (normal setting) and then continues going up slowly until 100°C (that's when we turn the engine off). The engine is fully new, the radiator and water bomb are refurbished. Do you know how can we correct this temperature failure?

From the profile of Juan a new user of JowettTalk.

[Keith Clements]

Hi Juan,
Thanks for following my advice and joining JowettTalk.
There are some initial questions to resolve whether it is a leaking head gasket, a blocked radiator, ignition timing or petrol/air mixture.
Symptoms of a head gasket failure can be bubbles in the header tank which can be seen if the radiator is over filled and the cap left off, or you can usually see moisture inside a cylinder by taking out a sparking plug, you can also investigate with an endscope where there may be a clean part of the cylinder where the gasket is leaking. Most garages have a device to check for gasket leaks.

To test a head gasket blown between the cylinder and another port, do a leak down test. This pumps air into the cylinder and measures how much is lost. You can listen and look for the source of where the air is exiting.

To test the coolant system, do a coolant system pressure test. This is similar to the leak down test. Pressurize the coolant system, and see how much pressure you loose. If you loose pressure, it means coolant is leaking out somewhere.

Chemical Test: uses a plug and siphon device to seal off the radiator cap port so that any leaking combustion gases into the cooling system can be suctioned into the device and detected by a chemical reaction which changes the color of a special solution. A bulb aspirator is typically used to draw in air from the coolant system to mix with the solution and exploits the fact that the concentration of CO2 in such air from a leaking head gasket is going to be significantly higher than the 0.04% found in the atmosphere. A control test with exhaled breath is used to determine the solution is still good, since a reaction/color change is expected under the concentration of CO2 in exhaled breath which is 4% or 100X more concentrated than atmospheric CO2. The concentration of CO2 out a car's exhaust can be as much as 16%.

Gas Analyzer: used to measure hydrocarbons, i.e. uncombusted fuel. Demonstration by ScannerDanner using the fga-4000-xds

Smell: I've seen a technician smell a radiator and claim to smell exhaust or something he felt suggested a bad head gasket.

The usual cause for head gasket failure is incorrect cylinder liner height. There is a complex set up to get this correct depending on what gasket and what sealing ring is used at the base of the cylinder. There is also a possibility in a newly rebuilt engine of porosity or stretching in the block or crack in the head between ports which should be checked prior to rebuild. There is lots on JowettTlak about this and more if you join the club and then access the Library.

If the radiator is not new then I would recommend getting a new aluminium radiator. We have a good relationship with Coolex who can ship one to you. Although yours is refurbished it may have been fitted with a modern narrow gap core and this can cause problems.

If the overheating occurs at idle rather than when being driven hard then it is probably not ignition or mixture related. Javelins are susceptible to overheating at high altitude or over 30c air temperature but with good radiator and oil cooler should be OK for competition. We drove up the Rockies in 40 deg C plus at 7000ft with 3 people and loads of luggage.

If you are doing this test on a test bed then it maybe there is not enough airflow to keep the engine cool. An electric fan fitted behind the rad should help.

The heads should be checked for the correct sized waterways and usually need to be open up with a 1/4 inch drill. Always run with inhibitor in the coolant and antifreeze actually helps cooling.