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New engine running hot #1
timfred Tim Frederick Berkeley, CA, USA 1971 MG MGB GT	Posted: April 08, 2012 04:29PM Registered: 1 year ago Posts: 243

Started the rebuilt engine for the first time today...runs great but HOT.

I thought it might just be a bad/wrong new temp sensor, but a thermometer on the head reads over 200 deg F and radiator is boiling over into the catch tank.

Where to start troubleshooting this one?

- New 180 deg thermostat
- New water pump
- Old radiator, but it was fine on the old engine and I reverse flushed it before putting it back in.
- Electric Fan (always on for now)

I think the timing is correct and no signs of the mixture being way off. Oil pressure is 50-75 psi.

Any ideas? I guess my first task is to make sure the thermostat is opening...then what?

-Tim

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Re: New engine running hot #2
USAFAVIATOR Shawn M Omaha, USA 1967 MG MGB 1976 MG MGB 1977 MG MGB 1979 MG MGB	Posted: April 08, 2012 05:13PM Registered: 4 years ago Posts: 1,090

Sometimes a reverse radiator flush can actually do more damage than good. A new radiator is a good (low cost) investment in protecting your new engine. Aside from that, you mentioned that you think the timing is correct, did you time it with a light? I had the same problem with my 77 and found it to be a combination of my timing being too far advanced and the mixture on my SU's being off. Just a couple of thoughts, good luck and congrats on the new engine!

Edited 1 time(s). Last edit at 04/08/2012 05:14PM by USAFAVIATOR.

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Re: New engine running hot #3
GILMGA Gil Dupre Chattanooga, TN, USA 1962 MG MGA 1974 MG MGB GT	Posted: April 08, 2012 05:13PM Registered: 6 years ago Posts: 7,302

Breaking in may run a little hot. How is oil pressure?

Gil

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Re: New engine running hot #4
twigworker Jack Austin Blowing Rock, NC, USA	Posted: April 08, 2012 06:06PM Registered: 7 years ago Posts: 20,753

Long shot, but make dead sure that the coolant is actually flowing.

Another long shot...make sure that the ignition timing is correct and that the mix is good without any vac leaks.

Next fill the radiator up to the top of the neck and watch for bubbles before the temp gets too high.

Jack

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-------------I like to think that I don't service automobiles so much as I provide entertainment, fulfill dreams and revive wonderful memories --------------

I am in the northwestern North Carolina mountains, right up against the Blue Ridge Parkway. Lawn chairs are in the shop and always time to talk. Drop in any time.

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Re: New engine running hot #5
j-blueridge Jamie Bourland C'ville VA, USA 1968 MG MGB GT "Antichrist"	Posted: April 08, 2012 08:09PM Registered: 8 years ago Posts: 648

I don't know anything about you or your engine, but I've been reading up on camshafts... could the cam timing be off?

I'd retard the timing so it still runs, see if the colling system is truly full (Jack and the bubbles) and I'd probably stand there and spray the radiator with cool water from a garden hose while the engine ran with the radiatorcap off. Can you see the water flowing? Big burps of air? Take the thermostat out and run it like that. Is it the same? Turn the heater on full blast to drain heat away (you may have done this.)

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Re: New engine running hot #6
kuz1 Keith Kuzma Prattville,Alabama, USA 1971 MG MGB 1980 MG MGB Limited Edition (LE)	Posted: April 08, 2012 08:16PM Registered: 5 years ago Posts: 2,724

how much over 200? that doesn't seem too hot to me .

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Re: New engine running hot #7
timfred Tim Frederick Berkeley, CA, USA 1971 MG MGB GT	Posted: April 08, 2012 08:49PM Registered: 1 year ago Posts: 243

I'll re-check the timing. I timed it with a light, 10 deg at idle, but I'm not 100% positive that the timing mark is in the correct spot.

It is hard-starting until warm, even with the choke fully engaged, so there is timing/mixture tuning to be done. But I didn't think the mix could be off far enough to do this.

I *think* the coolant is flowing because it burped when I first ran it after filling it (and then I topped it off). My best guess is that the coolant is running 215 deg F or so before I shut it down. I do have the heater valve open, but I forgot to feel that hose to see if it's getting hot.

-Tim

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Re: New engine running hot #8
timfred Tim Frederick Berkeley, CA, USA 1971 MG MGB GT	Posted: April 08, 2012 08:56PM Registered: 1 year ago Posts: 243

Another thing - my first inclination was that the temp sensor was the wrong one. At room temperature it did measure a different resistance than the one that was in the old engine...any way to diagnose if I have the right sensor for my car?

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Re: New engine running hot #9
kuz1 Keith Kuzma Prattville,Alabama, USA 1971 MG MGB 1980 MG MGB Limited Edition (LE)	Posted: April 08, 2012 08:56PM Registered: 5 years ago Posts: 2,724

how you coming up with the 215 temp.

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Re: New engine running hot #10
NNN Norman Nalepa Florida, USA 1979 MG MGB "Chick Mobile"	Posted: April 08, 2012 09:09PM Registered: 3 years ago Posts: 1,334

Just a thought. If the fan is blowing hot air from the engine instead of drawing cool air from the outside would this not affect the temp? Yes it would.

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Re: New engine running hot #11
twigworker Jack Austin Blowing Rock, NC, USA	Posted: April 08, 2012 09:13PM Registered: 7 years ago Posts: 20,753

Let's start from the beginning...I am almost not inclined to wade into this one as it, well, it could be a long one...

Rebuilt engine? What was wrong with it before and what did you do to it?

Main thing: Use a candy thermometer held against the thermostat housing or an infra-red thermometer pointed at same to get a better idea of what the temperature actually is.

Clarify: Oil pressure is 50 at idle and 75 at anything over say two thousand?

There could be a zillion things wrong to produce excess heat, if in fact the thing is running "hot".

Excessive friction from piston rings, not enough coolant, poor coolant flow, poor heat dissipation, wrong mix, wrong timing, vacuum leak(s), yada, yada.

Jack

---------------------------------------------------- Services to Interesting British Automobiles-- www.jackscars.net ----------------------------------------------------------------
-------------I like to think that I don't service automobiles so much as I provide entertainment, fulfill dreams and revive wonderful memories --------------

I am in the northwestern North Carolina mountains, right up against the Blue Ridge Parkway. Lawn chairs are in the shop and always time to talk. Drop in any time.

How to advertise on this website

Jacks Cars - Services To Interesting British Automobiles Over 40 years of caring and capable services to British cars and their owners. For help or advice please call 828-295-0224, email to jackscars@charter.net or go to www.jackscars.net.

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Re: New engine running hot #12
ashtone808 ashton wells honolulu, hawaii, USA 1970 MG MGB GT	Posted: April 08, 2012 10:29PM Registered: 1 year ago Posts: 43

Why the hard start when cold?? Mark your distributor where it is now, then loosen the distributor, and while someone cranks the car over move timing advance /retard to see if you can get it to fire easier. You may have cam timing issues. Does the car have power where it used to? No power down low? more power up top? (retarded cam timing) more power down low, less power up top? ( cam advanced) Make sure to bleed the system for air, and also feel hoses when car is warmed up! If one of your hoses is so hot you can't hold it long, thermostat may be stuck! Worst case scenario, change the radiator. 100 bucks is well worth the piece of mind!! Good luck!

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Re: New engine running hot #13
timfred Tim Frederick Berkeley, CA, USA 1971 MG MGB GT	Posted: April 08, 2012 11:22PM Registered: 1 year ago Posts: 243

So I think I figured it out, but now I have a new problem:

Let's say you drain your coolant and a shop towel comes out.

If you don't tell anybody, are you still embarrassed? Does posting your bonehead move to the internet make you less of an idiot or more?

Thanks everybody. You can now go back to arguing about which motor oil is best.

-Tim

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Re: New engine running hot #14
ashtone808 ashton wells honolulu, hawaii, USA 1970 MG MGB GT	Posted: April 09, 2012 01:28AM Registered: 1 year ago Posts: 43

Haha!! thats a good one! The truth will set you free!!! No worries, Im sure all of us have done something stupid from time to time! Usually cause were in a rush to drive her after all that hard work! Best of luck to you!

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Re: New engine running hot #15
dickmoritz Dick Moritz Philly 'burbs, PA, USA	Posted: April 09, 2012 10:12AM Registered: 3 years ago Posts: 7,247

In reply to # 2035058 by timfred Let's say you drain your coolant and a shop towel comes out.

If you don't tell anybody, are you still embarrassed? Does posting your bonehead move to the internet make you less of an idiot or more?
-Tim

Actually it makes you a genius for your speedy diagnosis... thumbs up

Plus, you get a gold star for honesty -- hey, we've all been there... smileys with beer

Dick

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

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Re: New engine running hot #16
NNN Norman Nalepa Florida, USA 1979 MG MGB "Chick Mobile"	Posted: April 09, 2012 10:25AM Registered: 3 years ago Posts: 1,334

And here I thought by backwards running fun was the answer. Only to br trumprd by a rag in the engine. Ya never know.

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Re: New engine running hot #17
BillB1 Bill Boorse PA, USA 1957 MG MGA Coupe 1974 MG MGB	Posted: April 09, 2012 12:59PM Registered: 6 years ago Posts: 306

Tim,

Good job on the diagnosis. And thanks for letting us in on your discovery. Just when I think I've done every knuckleheaded move a mechanic can do, all I need to do is read this forum to know we're all in the same boat.

Norman,

It's not possible to run the fan backwards. If it's installed backwards it will be a little less efficient due to the shape of the blades, but it won't move air the other direction.

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Re: New engine running hot #18
BruceH Bruce H Norwell, MA, USA 1955 Austin-Healey 100BN1 1964 MG MGB 1971 MG MGB GT	Posted: April 09, 2012 01:17PM Registered: 5 years ago Posts: 1,352

this thread is a classic!

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