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Thermostat going bad?

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Thermostat going bad?
#1
JR74 JASON ROBIRA
MIDDLE VILLAGE, NY, USA   USA
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1978 MG MGB
Took the car ('78 mgb) out this morning and noticed the temp gauge heading into the red. Coolant level was low so I topped it off. Didn't notice any coolant leaks but decided to turn around and figure out what was up. On the way back home it started towards the red again AND then dropped back down to it's normal running temp. Thought all was cool for a few minute or two UNTIL it started back up into the red.
Pump seems to be working as far as I can tell. Fans were operating as usual. Could this be a symptom of a bad thermostat?

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Re: Thermostat going bad?
#2
ingoldsb Avatar
ingoldsb Silver Member Terry Ingoldsby
Calgary, AB, Canada   CAN
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1971 MG MGB
Possibly - but I've also seen that happen (not on an MG) when there was a coolant leak. If the fluid gets low enough that the pump only intermittently gets access to coolant, the temperature can go up and down.

So, I'd find out if (and where) you are losing coolant and change the thermostat. They are so inexpensive as to make changing it an obvious thing to do.


Terry Ingoldsby
terry.ingoldsby@DCExperts.com

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Re: Thermostat going bad?
#3
Michael74MGB Avatar
Michael74MGB Michael Austin
Odessa, TX, USA   USA
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1974 MG MGB MkIII "Maggy"
This could be indicative of a T-stat sticking closed...or a partially blocked radiator... or a failing temp sender/wiring/voltage stabilizer issue... BUT a T-stat is a simple part to replace and a logical starting point.


74 MGB: APT VP11 cam, lifters, valve springs; 9:1; ported head; TT exhaust; vernier timing gear; wizard aluminum radiator; dizzy by Jeff S.; stock HIF4's; it goes on and on.....

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Re: Thermostat going bad?
#4
JR74 JASON ROBIRA
MIDDLE VILLAGE, NY, USA   USA
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1978 MG MGB
Suggestions as to which thermostat to replace it with?

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Re: Thermostat going bad?
#5
dickmoritz Avatar
dickmoritz Platinum Member Dick Moritz
Philly 'burbs, PA, USA   USA
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A 180 from any auto parts store. Ask for a thermostat for any 1960's or 1970's Chevrolet V-8. Cheaper than any "British" thermostat and fits and works fine. You'll need an MG-specific gasket...

Dick


Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

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Re: Thermostat going bad?
#6
bencii Silver Member Ben Colpitts
Eden Prairie, MN, USA   USA
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1966 MG MGB
1973 MG MGB
You can make a gasket with gasket material. Just use the cover to trace and cut with a razor blade/exacto knife. I always test new thermostats in a pot of boiling water with a cooking thermometer. If the retaining nuts or bolts are rusty and don't move easily, then stop and soak with a mix of ATF & Acetone or your favorite derusting fluid. The studs can snap off and make extraction more complicated.
Check the heater valve, just above the distributor.
I would also check the oil. If it's a milky color, the water and oil have mixed. Did you notice any white smoke while running? Hopefully your coolant loss is due to a loose hose connection or hose failure, collapsed internally. Also anytime you have an overheat problem you can turn on the heat. In provides additional circulation and will keep things cooler for awhile.


Ben
1966 MGB Tourer
1973 MGB Tourer

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Re: Thermostat going bad?
#7
ingoldsb Avatar
ingoldsb Silver Member Terry Ingoldsby
Calgary, AB, Canada   CAN
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1971 MG MGB
I can suggest a thermostat to NOT use. Don't get one of the "failsafe" thermostats. If you examine them carefully you will see that what they mean by "failsafe" is that, should the engine overheat, the diaphragm (or gate) is pushed open beyond its normal position and engages with a little catch. This prevents the thermostat from ever closing again. So, if you do overheat and drive it to failsafe mode, you have to replace the thermostat or drive with it forever open.


Terry Ingoldsby
terry.ingoldsby@DCExperts.com

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Re: Thermostat going bad?
#8
B-racer Avatar
B-racer Jeff Schlemmer
Shakopee, MN, USA   USA
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1950 Willys Jeep Pickup "Ratrod"
1964 Land Rover Series IIA
1971 MG MGB
Ask for Tstat 300-180, Mr. Gasket #4364 aka 825-1007. They come under many brand names but have 3 large windows to flow through on top.

They start to open about 10 degrees sooner than a normal stat to prevent those overheating surges.


jeff@advanceddistributors.com

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Re: Thermostat going bad?
#9
Speedracer Avatar
Speedracer Platinum Member Hap Waldrop
Taylors, SC, USA   USA
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1967 MG MGB Racecar "The Biscuit"
Most of the big chain parts store carries them as they must fit other applications, The blue Felpro is a lot nicer gasket than the cork ones.

Here's the one you want, if you Google "MGB Thermostat gasket" it will come up at all the chain part stores.

https://www.autozone.com/gaskets/thermostat-gasket/p/fel-pro-thermostat-gasket-25583/225056_0_0?spps.s=163&cmpid=LIA:US:EN:AD:NL:1000000:IEN:19489353538&&CATARGETID=120054150001289781&CADevice=c&gad_source=1&gclid=Cj0KCQjwltKxBhDMARIsAG8KnqVyg1CRLdrlMuoZaBjrj7Pm8uIBXyal1tn-kt_lmw-Dxc14NM67UyQaApgREALw_wcB&gclsrc=aw.ds


Hap Waldrop
Acme Speed Shop
864-370-3000
Website: www.acmespeedshop.com
hapwaldrop@acmespeedshop.com


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Re: Thermostat going bad?
#10
MGUK Paul Wiley
Watton, Norfolk, UK   GBR
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1977 MG MGB GT
If the thermostat is jamming closed the engine, particularly the cylinder head will be hot but the top hose and the radiator will be warm not hot. This is also true if the coolant level is low or the pump is not doing a good job.

Start by changing the thermostat - not expensive and relatively easy to change. Make sure you get the engine free of air when you fit the thermostat. Air in the cylinder head is a nuisance as it blocks the flow of coolant and almost always results in the radiator cap spewing hot water.

To check temperatures, invest in an infrared temperature 'gun'. It will cost about $30 and is a useful tool to have for everything from checking the temperature of small children, radiators (car and domestic), the oil in the sump of an engine and the contents of your freezer.

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about 1 week and 4 days later...
Re: Thermostat going bad?
#11
jimb Avatar
jimb Jim Brown
San Francisco Bay Area, USA   USA
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1958 MG Magnette
1967 MG MGB
It seems like the blue felpro gasket isn't available anymore. From two different sources, I've just get a ProTemp "equivalent" made from a different material and with a different shape. Both sources advertise it as a felpro part.

In reply to # 4792512 by Speedracer Most of the big chain parts store carries them as they must fit other applications, The blue Felpro is a lot nicer gasket than the cork ones.

Here's the one you want, if you Google "MGB Thermostat gasket" it will come up at all the chain part stores.

https://www.autozone.com/gaskets/thermostat-gasket/p/fel-pro-thermostat-gasket-25583/225056_0_0?spps.s=163&cmpid=LIA:US:EN:AD:NL:1000000:IEN:19489353538&&CATARGETID=120054150001289781&CADevice=c&gad_source=1&gclid=Cj0KCQjwltKxBhDMARIsAG8KnqVyg1CRLdrlMuoZaBjrj7Pm8uIBXyal1tn-kt_lmw-Dxc14NM67UyQaApgREALw_wcB&gclsrc=aw.ds


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Re: Thermostat going bad?
#12
Arizona Shorty Avatar
Arizona Shorty Greg McC
Prescott, AZ, USA   USA
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1968 Jeep CJ-5
1975 Yamaha MC RD350
1977 MG MGB
1985 Jeep CJ-7
It doesn't say it is a fel-pro part, it says it replaces a fel-pro part. All that suggests is that both will install in the same place. It does not speak to materials or quality.


GMc


Wait for me at the gate Tuffy, because without you they're never gonna let me in.

SDCH WTCH-X Twin Oaks Tuff Nutt
2008 - 2022

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Re: Thermostat going bad?
#13
ClayJ Avatar
ClayJ Silver Member Clay Johnston
Mt. Olive, MS, USA   USA
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1972 MG MGB
As noted low coolant can cause loss of movement, air-bubble in the head can cause the gauge to read low; either can lead to overheating.

If you think the coolant is low, it needs to be topped off at the plug on top of the thermostat housing when cold (i.e. burping the cooling system). With heater valve open, remove plug, add coolant, start engine at idle, keep adding coolant, when it starts to push out reinstall plug.

The expansion tank on the fender only needs about 1/4 coolant when the engine is cold, just enough to cover the pickup tube.

Verify the cooling fans are coming on when they should, the thermo switches at the top right of the radiator do go bad.

Verify both fans are actually working if one fails it will move in sympathy with the working fan but won't move much air. To test, unplug one fan and jumper across the thermo-switch, the fan should run, swap and test the other fan.

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