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MG MGA - Overheated... sort of but not really.

This is a "what would you do" thread. Here's the scoop...

Driving to a fun run a few days ago, I felt a sudden sputter. Moments later it happened again and continually got worse. I knew exactly what was happening as I coasted into the parking lot (whew, just made it!). My fears were confirmed... the heater valve had leaked all over the dizzy. I shut the valve, dried the dizzy and began the drive into the hills.

On the first climb, the temperature shot up like a rocket. So fast in fact that I didn't believe it could possibly be accurate. The car was running flawlessly as usual but as the temp climbed past 230, past 100lbs oil and on up to 80 lbs oil, I pulled off and shut it down. Steam began to howl out of the radiator overflow.

It turns out that the heater valve had leaked so much coolant that the system was no longer pumping anything. I was a full gallon low! I let it cool to 220, started the car for 15 seconds just to get momentum down the hill and coasted to a grocery store. While pulling away the car still ran perfectly with no signs of anything wrong.

I filled up the cooling system and continued on the fun run through the hills for the next 4 hours with no problems whatsoever. So...

I'm assuming that it was only the air in the system that got so hot and that there is no damage to the head or anything else. What is the consensus of the group? Should I leave it be, should I retorque the head, or should I pull it apart. I'm inclined to let it be although in the back of my mind the head may have moved a little or the studs may have stretched a bit at those temperatures.

Opinons? Advise? Thanks!
Steve Simmons

Almost forgot to mention... this is an early 3-main 1800 block and head.
Steve Simmons

It sounds like it survived ok. I would continue driving with a close watch on oil and coolant for any cross contamination/leaking, and if temperature and pressure remain ok it's fine. You should know soon enough!
Neil McGurk

With a cast iron head you should be OK. If there was still steam there must be water and the engine was not dry. You say it was not pumping water, but if the water was below the pump level and not circulating the water left in the radiator would not get hot. If steam was being given off I believe that water must have still been passing over the hot areas.
Steam is good, no steam is bad, for an overheating engine.

Mick Anderson

Steve, Back in the early 70's, I worked at a busy service station while going to college. We had a particularly hot summer and cars would regularly come into the station low on coolant for what ever reason. This was really not that unusual and at that time most cars had cast iron cylinder heads and cast iron blocks. Not many (if any) were affected by these bouts of overheating. Today, we are not used to this happening with higher pressure systems and coolant recovery bottles. Your car is probably just fine.
James Johanski

It sounds like you lucked out. The first sign that you really cooked it normally is sticking valves as the head gets the hottest first. This will be fiollowed shortly by the engine slowing down as the psitons become one with the cylinder wall. Just watch your oil consumption, if it increases you may have scorched the rings or a cylinder wall but from what you posted I think your engine be fine
J Heisenfeldt

Thanks all, that's encouraging advice. I'll play it by ear and not touch anything for now.

It is indeed an iron head. What really scared the crap out of me was how high the temp needle went. I didn't realize it was physically possible to do that! If I had revved the engine a bit I may have been able to make the oil and temp needles collide! LOL!

I assumed the coolant was no longer circulating because after cooling down, I started the engine and the temp did not change at all. Normally I would expect to see the needle drop a bit as coolant passes through the system, just as when you stop for an errand and the needle goes up, then back down when you start the car again. I was exactly 1-gallon low so maybe that wasn't quite enough to starve the water pump.

Thanks again!
Steve Simmons

Sounds like no harm done. With the conventional style cooling system the block fills from the bottom to the top and then the head. The water pump will empty the radiator until it sucks air, filling the block and head and forcing any extra fluid back into the radiator. With the MGB, the temp sender is located fairly high in the head, so will be one of the first things that is not covered by cooland when the level gets low. In the worst case the fluid level gets so low that eventually there isn't enough to fill the head and you start to see valve and gasket failures , the latter mostly due to the head being so much hotter than the block which still has coolant in it and the fact that the main heat source is the combustion chamber at the head block interface. Cracked heads are also common. Common problems with a dry block overheat are oil control issues and lack of compression due to piston ring relaxation because of the heat.
Most engines will survive a modest overheat such as you describe without major problems at least once or twice.
Bill Young

Hey Steve, is it time for a New Year's day run?. Wanna race and we both have our heaters on. Oh hell, I gotta be fair, close that damn thing and we go head to head or I may say your car to the rear of mine as I will be in front!!!!. I hope it doesn't rain, but if it does we need it.

You're an evil man Jeff! I know all about the blown 5-main you have under the bonnet! :) A New Year's run may happen since people have been talking about it. Keep an eye on the So Cal forum. That's where it will be announced.
Steve Simmons

Steve, what is the site for the S. Calif Forum where you will list it.

Sorry, I thought you had it.
Steve Simmons

This thread was discussed between 19/12/2007 and 22/12/2007

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