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MG MGB Technical - Cabin heat, MGB-GT

Help!
I have a 1971 MGB-GT and during the summer the heat within the cabin can be pretty bad. I have made exhaust shields out of stainless steel at the manifold and between the floor board and the exhaust pipe. I have located and plugged all holes that I could find in the bulkhead. Lot of heat comes from under the dash and off the transmission hump and shiffter. The engine runs fine during mild weather but gets hot (190-200 deg. F) during days that our over 90 deg F outside. New radiator, alloy head, elec. fan and new water pump & thermostat. I even installed a ball valve down stream of heater core to block water flow that may get past the heater valve. With all this said it is still sometimes is unbearable during the hottest summer days. I plan to install an A/C system but may not be able to use it when I need it the most.


Ron
R Garcia

Do you have good insulation under your carpet? If you check the archives there are many options such as Dynamat. It shouldn't get THAT hot. Do you have an oil cooler? Are you using a 165 degree stat or a 195?

Jeff Schlemmer

Two issues here:

1. Cabin uncomfortably hot.
2. Engine overheating.

1. In twenty years and at least a dozen MGB drivers, only one 1800 ever overheated on me. The others have always run cool. My current 74.5 GT barely gets off the "C" pin. This is not a problem that I can't address. It has a 160-degree thermostat in it and I'll get around to a 190 one of these days. Now that daytime temps are getting into the 80s here in the Virginia mountains, my temp needle does get halfway up to the "N". This isn't the sender or gauge - the air coming out of the heater is luke warm at best.

My point is that the only overheating 1800 I've ever owned and driven was in pretty bad shape. The oil pressure wasn't great either. I sold the car long ago.
So, if your engine is overheating, you might check into the general condition. Even check simple things like timing.

2. As for cabin temperature, at road speeds it makes a huge difference when you open the rear quarter windows. Does your car have the under-dash liners? Usually they're missing on these cars but Moss, etc, sell replacements which might block some of that under-dash heat. Also, they cut down on noise level. '72 and later MGBs had both a rubber and a vinyl boot for the shift lever. ' Can't recall if an arrangement like that would work on a '71. Certainly it would if you use a later style console. None of this is "instead" of the insulation Jeff suggests. Do that too.

Maybe you can bottle some of that cabin heat and sell it to guys like me in the winter time!
Allen Bachelder

Jeff,
I checked under the carpet and guess what! No insulation.
I have an oil cooler that is about 2 years old.
165 deg. on the thermostat.

Allen.
I rebuilt the engine about 3 years ago, still getting around 70 psi @ idel.
Timing could be an issue. The block that I have is not original and is missing the engine tag. It is a 5 bearing with casting mark of “8 25 67”. The timing for different years jumps around. I found that 14deg seems to work for me, could be wrong. I do have under dash liners. During average weather the engine runs just under “N” on the temp gauge and the cabin is fine. It is when the temp is over 90deg. F and I’m on my way home (Going up hill around 1000ft in 30 miles) that this situation occurs.

Thanks for your input
Ron
R Garcia

Well, so much for the tired engine theory, the timing theory and the dash liner theory. Put in some floor insulation as per Jeff, open the rear quarter windows, maybe put double boots on the shift lever as per above and see if it gets more liveable. ' Sounds like your engine is probably not overheating at all - you're just getting a lot of it transfered to the cabin. I do find that I can't turn the heater valve all the way off with the control - I have to use a screwdriver to push the tab in the valve all the way to the end of the slot. But it sounds like you've attended to that already.

The issue for me is getting some heat out of it in the winter. Sure, I need a higher temp thermostat, but I ran it most of this winter with carboard covering 3/4 of the rad and still very little heat, unlike a '72 midget I sold last year that just poured out the heat in the winter. Same heater, smaller engine... Of course much less space to heat too, but boy did that thing work!

Cheers,
Allen
Allen Bachelder

Had 1 BGT LE that was very hot in the cabin, ignition timing well out, corrected and alot cooler in the car.
Ian

I feel your pain.

It was 103º F in L.A. a couple of days ago.

Idling at successive, multiple stop lights became
rather tense as the Temp guage needle traveled
up the scale. At least, it survived.

Short of installing an AC, I had thought about clipping a small 12V DC muffin fan somewhere
in the cabin to blow air on the pilot (me).

Just an idea.
Daniel Wong

i used to have a Midget that did this evey time we took it out in the heat turned out to be thermostat stuck down now i never use on in my GT also use some water coolant always helps i suppose over there there is no need to antifreeze so just get soemthing like water wetter very good stuff
Nathan

What about a Webasto type sunroof?
Dave
Dave Wellings

Daniel,
I was stuck in traffic in Riverside on the day it was 103deg.F so I know you understand what I’m talking about.

Nathan,
This wetter water works? I will try anything at this point.

Dave,
If I could find a Webasto that I could afford, I would get it. I have looked but have not found one in my price range. They do look good don’t they.

Thanks Guys
Ron
R Garcia

Ron

Water Wetter works. Available in the Redline products section at most auto parts stores. Also a good writeup on it on the Redline web site. I use distilled water with water wetter and a water pump lubricant additive in my A.

There are some threads on this topic in the archives. Check both A and B archives and search on "water wetter".

FWIW

Larry
Larry Hallanger

Lots of heat here in FL as well. I insulated my 74 GT real good and it made a big difference. I also have the dealer installed A/C with the York compressor.... blows out at 36 - 40 degrees. But without the added insulation the it was still too warm.
Bob
Ribert Ritter

they are desgined to be like that boiling in summer freezing in winter.
John smith

I am afraid it may be the nature of the beast. With ambient over 90, going up-hill, your engine will get warmer than normal. I do not see a problem unless you are boiling over.

The problem is caused by that great mass of air that is trapped under your hood. In an MG, there is not a lot of place for that air to go; talk to the V8 people about this one! Just for fun, next time it is really hot, take the hood of the car and climb up the hill to see if it makes any difference. You might want to consider louvers in the hood.

Pete
Pete

BTW, I had mentioned in my response to this question on the B General board about the heat shielding material I had used. I just noticed today that you can buy this same reinforced foil/shredded rag insulation material at Home Depot as Hot Water heater insulation. At our store it goes for around $20 per kit enough for one large water heater. FYI.
Bob Muenchausen

We've had many long drives in 100-degree ++ temperatures with several Bs and with our 1800 Magnette. Temperatures up to 108 degrees F going across Kansas last summer. ' Never had an 1800 overheat. Now The Navigator... that's a different story!

John Twist said it: the best thing you can do to avoid overheating is put a piece of tape over your temp gauge! If smoke/steam aren't billowing out from under your bonnet, you're not overheating. In my case, even the temp gauge has always been happy. Sometimes near the left leg of the "H", but never into it. I've never used Water Wetter but I do run around 60-70% antifreeze year-'round.

That doesn't mean the cabin doesn't get warm. Very warm... I'm planning on A/C in my 74.5 GT when I get the V8 in, but first - as per Bob Ritter - I'll insulate, insulate, insulate!
Allen Bachelder

Glad to know I'm not the only one with heat problems. Stuck in traffic, needle goes towards hot but never boils over. I run water wetter along with anti-freeze.
George Lee

One thing you did not mention is if the heat from under the dash might be coming from the heater. I found my heater valve was not closing all the way so it was actually putting out heat into the cabin all the time.

Bruce Cunha

For those interested, check out thread on T-stats on the MGB General board. There may be some helpful info there.
Bob Muenchausen

Bruce,
I added a ball valve some years ago on the heater water out line and close it during the summer. I have pulled the dash so I can insulate and found that the 2x3 rubber plug behind the brake assembly had fallen out.
Ron
R Garcia

My TD firewall has "extra" holes. In the case of the TD, in the spring and fall, the extra heat is a welcome addition. One of the reasons I got a BGT was to have something a bit warmer in the early and late part of our driving season.
Bruce Cunha

This thread was discussed between 29/04/2004 and 07/05/2004

MG MGB Technical index

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