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MG MGB Technical - underheating

i know this goes against the trend but it seems my car engine temp never quite reaches normal. on the guage the needle sits a bit to the left of 'N'. what i wish to know is there any problems with the engine temp not getting up to normal?

my car is a 72 b with a GG engine and one of the std later heads that is supposed to promote cooler running. i have recently changed the thermostat and it has made no difference.
phil tavaria

Phil-
Where did the needle on the head sit prior to the head change? Did you use a different temperature sensor when you installed the new head? Have you tried putting a cover over the oil cooler?
Steve S.

Automotive gauges are often inaccurate; that is one reason that they are marked with such ambiguous things as H, L, N, C, etc. Another reason for such markings would be to keep people from worrying when the temperature is at 220 F or 107 C. Check the temperature with an accurate thermometer and find out what it actually is. The thermostat bypass may be allowing too much water to flow through the radiator when closed. Many people mask part of the radiator in the winter to prevent over-cooling and to get a little more heat from their heaters.
George B.

I have a '67 MGB GT with a mechanical temp gauge that DOES measure accurately. I live in the Seattle area with a climate similar (I've been told) to that of England. In the winter when the temperature is in the upper 30s(F), my engine never runs anywhere near the rated temperature of the thermostat. I block off about 3/4 of the radiator and all of the oil cooler (though now I have an oil thermostat). With a 195F thermostat it runs approximately 170F when thoroughly warmed up (straight and level highway driving). It's quite interesting when I first start out, watching the temperature needle slowly approach the 195F area, then quickly drop to 160F or less as the thermostat opens. It cycles like this a few times before finally stabilizing around 170F.
Apparently at this ambient temp the sump and block radiate enough heat into the cold air to seriously affect the coolant temperature.

Regards,
Jerry

Jerry Causey

Phil,

I would guess that maximum power is obtained from the engine at about 75deg C (170F). This temp is probably low for a road car as the oil is not hot enough to do its job (Oil prob should be 100-110deg C). Oil themostats are usually 80deg C. An ideal temp is prob about 90deg C as the oil usually runs about 10deg C hotter. The N should be about this temp and slightly to left should not be a problem on cold days when temp is around freezing, but in Summer should be on N, subject to guage being correct. I hope not as mine is running slightly to the left during the cold weather. As Jerry points out the needle will swing to the left as the thermostat opens for the first time and during this stage of the cycle I do not push the car until its fully warmed up.

Paul

Paul
Paul

Jerry - if you can see the stat opening and closing a few times on the gauge then stabilising (as mine do) then I would say that your water temp through the stat is the same as it always is, but if your gauge reads lower in winter than summer then it is the gauge reading that is different not the water temp. It simply isn't possible for the stat to have a different opening point in different ambients. What *is* possible, as you say, is that sump, block surface and heater cooling in very low ambients means that the coolant never gets hot enough for the stat to *start* opening and this can cause a low gauge reading, but you will not see the stat cycling under these conditions.
Paul Hunt

Paul

If using a 195F (88deg C) Stat then at 170f the stat would probably not be open, depending upon temp range the stat starts to open to being fully open, so must be ambient temp keeping water temp down, either that or the stat is actually balanced on a mid point of opening.

I use a 82deg C stat which I assume is fully open just left of N and my sleight variation is again due to ambient temp, which would be less apparant with a 88deg C stat, but I live in South so not usually that cold. What is noticeable is the large drop in temp when in winter when very cold water enters the system, perhaps a heated garage is called for.

Paul
Paul

Paul, Surrey - that's what I mean't, if not actually said, when I wrote that a 195 stat would not be cycling at 170. And especially wouldn't be cycling at a different temp in winter to summer. I too get the temp drop when I turn the heater to 'hot' if it had been at 'off' since starting, and that would tend to close the stat until the coolant temp gets up to the stat opening point again. If the stat is fully open whilst travelling at speed in very low ambients then it will be unable to maintain 'N' in higher ambients. If your temp gauge is stable and on 'N' the stat must be somewhere between fully closed and fully open. If block etc cooling increases when the stat is fully closed then the temp gauge will start to drop below 'N'. If heat output increases when the stat is fully open then the temp gauge will move above 'N'. Anything between those two extremes and the stat opens more as heat output increases, less if heat output reduces, to maintain a relatively constant coolant temp.
Paul Hunt

Speaking of heaters ...
I put the new fuse switch in myself (boy I'm pretty proud of that!), flipped the switch and it worked! But I've got no hot air. The temp. guage says that the engine is 120 degrees when warmed up. Its never gotten any hotter. Do MG heaters run off the water in the radiator? Do they have their own heating elements? If it should heat off the radiator then, after I check the thermostat to make sure its working, should I block a portion of the radiator to get the water hotter? If so, how and how much blockage?

Speaking of the new heater switch, thanks to you folks for telling me about Peter C. at World Wide Auto Parts of Madison, Wisconsin. He got me my switch and my shocks in record time!
Margo Lubbers

See other posting (and don't double-post)
Paul Hunt

Ok, Paul, sorry.
I have found a wire to the heater know that wasn't hooked up when that mechanism was replaced. The bolt, nut and clamp are not anywhere to be found. I figured that I would just run the wire thru the nut hole and wrap it around the mechanism. But there really isn't much room to work inside of the dash. So I was going to take the know off and do it and them put it back in. The instructions say to puch the shank in to get the knob off. What's a shank? Is that the silver disk in the middle of the knob? If so, that baby isn't moving.
Can you help??!!??!!
Margo Lubbers

Margo,

On the side of the knob, there a little hole. Inside the hole there is a spring and ball setup.

Depress the inside of the hole with a small screwdriver or punch, (carefully), and the knob will slide right off.

Hope this helps!

David
David

I think you will have to replace the proper wire clamp. The wire both pulls the valve closed *and* pushes it open, wrapping it will almost certainly result in even more play than usual which will greatly reduce the amount of movement and hence heat control at the valve.
Paul Hunt

195ºF t-state? The hottest thermostat I can find is an 88ºC, which, if my memory (from a required college chemistry course) of how to convert F to C is 190.4ºF …is it just called a 195 Tstat or is there really one out there…..by the way, the part removed from the engine and in the drawer is an 82ºC (179.6ºF) Tstat, I removed it because the temperature gauge “wandered” colder as I increased speed in the now frigid rolling hills of eastern Pennsylvania. The 88 Tstat provides a rock solid “N” after a brief warm up.

rn
RN Lipow

This interesting thread together with Steve S´s article on engines made me change my thermostat today from the 82 one to the 88 and WOW what a diference. My 69 B was always cold (left of the N ) and now it bounces arond the N and reaches temp quicker. I had already covered the oil radiator with no sucess. What I also noticed was the previous thermostat had three small holes (four mm wide)around it and one had a ball just a bit biger the the hole hanging on it. I dont remember wether the ball was "over" or "under".
I only hope I´m not runing to hot now.
Happy New Year everyone
Miguel
Miguel

This thread was discussed between 17/12/2001 and 26/12/2001

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