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MG MGB Technical - Over Heating

I have a 77b and it's overheating, up in the red almost.

Replaced the water pump, t-stat and installed a re-cored radiator. Also put in both temp sensors.

Tested the radiator sensor, it's new but off spec by 5 degrees.Kicks on at 203 and off at 185. Didn't test the other new sensor. Also put in a 180 t-stat.

At freeway speed it cools, not where it used to be still hot. When comming down from speed is when it gets real hot or stop and go, when idling it gets hot until the fan kicks on at almost red then comes down to 3/4's.

Also have had problems with the carb, runs rich, not to bad but rich should mean cooler, cooler than lean.

Any idea's?

Thank you,

kb.

Kevin B

Kevin - When you say that your car is getting hot, dos it start to miss or is it boiling (steam coming out of the radiator)? 203° F is not really overheating unless the temp continues to climb to the point of boiling. Have you checked the temperature gauge to insure that it is not lying to you? If the fan is bringing the temp back down to 3/4 scale, I would say that things are operating the way they should. With a 180° F thermostat in the car, 180° to 185° is the coolest it will run (a thermostat sets the minimum temperature the system will run at and has very little effect on the upper temp). Finally, what type of radiator core did you have put in the car. If it was something other than one of the Modine units (4 row L type or the HER cores) or equivalent, that may be the cause of the elevated temperatures, but I would not call them excessive.
Good luck - Dave
David DuBois

It has not reached the boiling point yet. Not sure what type of core they put in, I will call and find out. Also, I do get a miss after it's been running for a awhile, also get a little pop out of the carb now and then. I adjusted the timing about a month ago, I'll double-check it again tonight. How do you go about testing the gauge? I also asked the garage if the radiator had been flow tested, they said they flow test each one. When I got it back there was not a drop of water in it. If I hooked up a regular garden hose and run it through, I should see full flow? Is that enough pressure to test for restrictions?

What you say makes allot of sense, the gauge will read almost to red before the fan comes on, that should mean that the coolant is at 203 degrees. Unless the new t-stat is sticking or the radiator has low flow or the gauge is faulty. Would that be the right line of thought?

kb.
Kevin B

They said they used a Graig Core, same number of rows. Anybody know anything about these?

Thank you,

kb.
Kevin B

I agree with David. If it isn't losing water or steaming it isn't overheating. The fan switch should cut in at 90C/194F, and that should be about mid-way between N and H. In my experience the gauges normally run at N, which with a standard 82C/180F stat implies about 8 degrees from N to mid-way, so maybe a similar amount from mid-way to H i.e. about 98C/208F, which could explain why the fan isn't coming on until it is nearly in the red. Even so I'd expect running at 60mph or so in free air even in ambients of 80F to see the gauge come down to N given enough time, if not maybe the gauge is reading high as well as the fan switch coming on late. But I think RBs tend to run hotter anyway. You should be able to run it up to temp until the fan cuts in with the rad cap removed without it boiling, with a thermometer in the filler plug sealed with rag to limit coolant loss, and so see what the temp really is.
Paul Hunt

Thank you both, I appreciate it! I'll definitely try the temp reading from the filler plug. Let you know what I find.

kb.
Kevin B

Kevin. You might wish to check out my website, www.custompistols.com/ then click on the MG section, followed by articles. There is an article on cooling system inspection which may be of use to you. It covers most of the tests you can perform at home.

I have been investigating the cooling system for several years now because our cars run so hot in Arizona summers. I have purchased an infared thermometer and will be picking up a spare radiator to have the Modine core inserted. Then, I will be able to list an actual series of heat readings to show if there is a significant difference between the factory radiator and the Modine re-core. In the mean time, my 68 GT is my daily driver. It will go almost to the H on the gauge in stop and go traffic and regularly runs above 3/4 on the highway in traffic. This has been working this way since I bought the car, something over five years ago, with no boiling over nor other problems. In stop and go traffic the engine will begin to run a little rough when stopped and the gauge is reading near the H position. This clears up when the traffic starts moving and the gauge moves downwards a touch. But, the engine has never gotten sufficiently hot to stall nor have I had problems with the head gasket. Les
Les Bengtson

Kevin, you stated

"when idling it gets hot until the fan kicks on at almost red then comes down to 3/4's."

My experience with the factory switch is that
it is set at too high a temperature for our
climate. As mentioned above, it should turn
on midway between N and H. Your switch may
be faulty.

I think you need a temperature sensor that
kicks in the fans at about 195 deg. Try a
discount parts store like Advance Auto Parts --
they sell an adjustable fan switch with a sensor
that is tied to the radiator fins. It's easy to
play with the adjusting knob to get the fans
to start at the right temp. The Kenlowe fan switch
(call www.brittek.com) is an alternative that
is also adjustable.

Ronald

Unreal!

I popped off the filer plug and snuck out the wife’s meat thermometer (thank you), t-stat opened on time at 180-5 then fan kicked on at 195 cooled down to a nice 180-5!

I watched the gauge actually break about two weeks ago, then started in on all the fixes! Unreal....

Used to read N consistently, just before the fans kick on it read 3/4s. I assume I can adjust the needle? Or would this be a gauge replacement?

Oh, before I get back to my carb, thanks mates!

Truly appreciated!

kb.

P.S. I was kind enough to wash the uh um, borrowed item....
Kevin B

Note to self: If invited to dinner by someone named Kevin in San Diego, don't eat the meat.
Steve Simmons

Kevin, I admire your resourcefulness. You know those meat thermometers cost about $1.95 at K-mart. You could buy the wife a new one as a gift, and keep the old one in your tool box. It may come in handy again, as you work with recalibrating your temp gauge or whatever else.

You could win points with this method: "Honey, I needed a meat thermometer to test the MG. I bought this new one, but it seems a waste to use a new thermometer on car repair. Why don't you take it, and I'll take your old one."

Matt Kulka

Kevin - in response to your question about the gauge, with electric gauges it could either be the sender or the gauge, or indeed the voltage stabiliser could be faulty. Unless you take voltage measurements wrt ground at the sender wire at a given needle angle and compare that with another car you won't know.

If the stabiliser is working it will be switching between 0v and some voltage about once a second, but it needs a couple of seconds after first switching on the ignition to 'warm up' (during which time it should show a constant voltage) and start switching. The voltage should be high when cold, dropping as the engine warms.
Paul Hunt

FWIW the electric gauge on my roadster occasionally shows the same trend and a shake of the wire running to the cylinder head sensor has always brought it back to "N" so far. Alarming the first time but a similar check showed the problem was the gauge. By the way I bought a jam thermometer. It has a better range and you stnd a chance of getting homemade marmalade. I don't mind the taste of antifreeze.
Steve Postins

This thread was discussed between 23/03/2004 and 27/03/2004

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