My '68 E-type (4.2) does fine when the weather is cool but at 76 degrees F when in traffic, the car heats up and will eventually peg the guage. I have changed the fans, purchased an alloy radiator from xk's unlimited, and used a variety of thermostats. I have used coolant system cleaners (prestone crystals) three times and have had the system backflushed twice. Nothing seems to work. Any ideas?

Submitted by NE52-32043 on Tue, 08/24/2004 - 14:38

Guy,

I know you said that you changed the fans, but are you sure that they are coming on? Don't assume that just because they are wired up, they actually work. You may have a bad Otter switch. It doesn't hurt to wire them to run constantly. That's how I had mine on my '72 2+2.

This may sound stupid, but are the fans turning in the right direction? I've seen them wired so they are blowing into the radiator rather than through it. Lift the bonnet and when they come on, put your hand behind them (both of them) and make sure they are actually drawing air through the radiator. If they are turning the wrong way, simply reverse the lead wires to each fan.

Mike Frank's comment about the water pump is one that you might want to consider. If the water pump has never been changed, it's possible that the impeller is badly corroded. In that case, it won't move much water, especially at idle.

Mike's point about checking the temps with an infra-red thermometer is a good one also. I know several people who had either defective gauges or defective senders and thought they had an overheating problem when they didn't.

Make sure you are not running too lean. Are you sure you are installing the correct type of thermostat? Have you changed the hoses? (Though soft, collapsing hoses are usually a problem as speed, not at idle.) What mixture are you using? Should be 50/50 anti-freeze and water, and add a bottle of Red Line Water Wetter.

Steve Weinstein, JTC-NJ
'70 XKE FHC
'84 Ferrari Mondial QV
former '72 E-type 2+2 owner

Submitted by mfrank@westnet.com on Mon, 08/23/2004 - 09:07

Usually, an aluminum radiator is efficient enough to cover any problem, so this is pretty serious. Since you say it's overheating in traffic, I assume you mean that it's fine at highway speed, but overheats in slow crawl situations.

A few things come to mind. First thing to do is to let the car idle until the temperature builds. Then use an infrared thermometer to measure the temperature at the thermostat housing and the water pump inlet. There should be a difference of ten degrees or more. If this is the case, your cooling system is functioning normally. If not, then it may be an obstruction, or your water pump may be functioning poorly (check the belt).

Look for a tuning problem. Very lean mixture, low idle speed, retarded timing. Check your valve clearances, cam timing, and make sure the timing chains are tight. And check your compression: a tired engine runs hotter.

Submitted by stuross41@eart… on Mon, 08/23/2004 - 08:20

You say that you "peg the gauge". Does the car actually boil over or does the gauge hit the top? My 74 Series III was "Pegging the gauge" and I was worried about it overheating. The mechanic took an infared thermometer and read temperatures all over the system, tank, radiator upper and lower hoses. They were all OK even when the gauge was reading near the top. He replaced the gauge and sender! End of problem.

1974 XKE OTS
2000 S-Type V8