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MG TD TF 1500 - Effects of Unleaded Gas on Engine Temperature

There has been some discussion on the effects of unleaded gas in raising the engine water temperature in a number of threads. Since these discussions have been hidden from the gereral populace since they were off topic I thought I would start a new thread here.

Basically there are a number of us who have the opinion that the newer unleaded fuels may be making our cars overheat. I cannot prove it but I myself and a number of people I talk to have been having overheating problems the last few years as the US phased out unleaded fuels where we never had them before.

Some of us have been driving the same car for decades and only since about the time the unleaded fuels became prevelant have we experienced this problem.

Anyone out there with some emperical evidence one way or the other?
Chris Couper

I've now had a 51 TD for almost 2 years. Last year we put over 6000 miles on it, and this year we have done about 3000 so far. Much of it at highway speeds, though we're far from the fastest out there. The car gets only unleaded, 87 octane, plus a lead substitute. Usually Redline lead replacement at 1 oz per 10 US gallons ( 1/4 oz (capful) per 10 litres). The car has never got hotter than 90C on the hottest day. It is set to run somewhat rich, as I'm told that running lean is the fastest way to overheat. The rad is 50/50 water and antifreeze.
Ted Jackson

Chris...I run the same setup as Ted on fuel and coolant mix and have never had a problem as temp never exceeds 85 deg even running at 4000 rpm in 90+ deg heat and 80% humidity. We just did a 1000 mile trip in those conditions.
I also run carbs a little on the rich side which may account for a measly 24 mpg.
colin stafford

Haven't driven my car that much yet, but the temp gague is always over 100 degrees, I seem to remember that cars are supposed to run at about 180 degrees for best performance,(info from old tune up class in the 70's) What is the normal operating temp? And what about using redline's water wetter?

Tom
Tom Patoine

For several years now the fuel formulations available in the US have burned hotter. I became aware of this whn my VW Bus and VW Thing burnt up engines on long trips. The shop that rebuilt the engines noted that they had had a lot of new business because of the new gas formulation. Particularly for people on long trips at expressway speeds. Their conclusion w that the gas burned hotter and the vunerable # 3 cylinder's cooling was not quite up to hanling the extra heat load.
In my TF and MGB-GT I have had to take measures to deal with the extra heat, good flushing, recored higher- efficiency radiator on MGB, using "Water Wetter" plus pump lube and pure water in both, plus careful attention to timing and carb adjustment. These have paid off in that both systems now do not overheat.
But the bottom line is that the additives in today's fuel do burn hotter.
Don Harmer

Before rebuild, my TD ran hot (up to 90+ C) on a hot day (but never boiled or quit). Between boiling the radiator and removing gobs of gunk out of the block it runs easily 10 deg. cooler. This motor was last boiled/cleaned around 1975, and had coolant changed irregularly. I may suggest that anyone with chronic overheating with all other causes checked could pop out a couple of the lower freeze plugs and see what is lurking back there- it was solid rusty muddy stuff when I popped out the lower plugs! Are there any chemists/engineers out there that could explain why unleaded may burn hotter? The lead conducted heat or lubricated valves/stems? Doesn't octane refer to the speed of burning of the gas (ie higher octane explodes more slowly)? Anybody have a clue?
George Butz

All the asundry comments about cooling are good but I would like to stay with the fuel idea here. But just to set the record straight:

I have a re-cored radiator, recently hot tanked engine, have tried water wetter and various degrees of AF from 10% to 80%, have checked timing and carbs, fuel pumps etc. My engine ran just fine until about 10 years ago with no change except the fuel. Also the temp gauge has been checked and is within 2 degrees.

My car runs in the 90's when the outside temp does. When it gets to about 100, so does my car. I cannot climb hills when it gets close to 100 F, the car pegs the temp. I can idle just fine when it 100+, around 94C.

The only thing I have not tried is a gas addititive. If anyone has any evidence that one would work I would like to hear it.

I am not alone in this area. I spoke to dozens of long time T'ers that have similar experience. TF's seem to fair better with the presurized systems. Also of course those TD's that have been so modified. Don't ask. :-)
Chris Couper

This thread was discussed on 02/08/2001

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.