MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - TD overheating at speed


Hi all, and help, please!

I'd like to learn whether my TD has a real overheating problem, or did I just get what I deserved?

A week ago Friday I left for Louisville from Michigan, (about 400 miles each way), top down, for a British Bash. Lots of fun there! I ran with a buddy driving his AH 3000. Another buddy was riding shotgun with me (we were beached whales in a sardine tin, 600 pounds, more or less, in the cockpit). Ambient temps hit the mid 90s F both days. We basically ran I-75 and I-71 both ways. Down, max water temp passed 100, showed 95 lbs oil pressure(!) on the dual gauge, @ 4000-4200 rpm; 90 (oil) home, @ 4200-4400 rpm. We made a few stops each way, and at each I raised the bonnet to help dissipate some heat. Pulling the choke made restarting ok. Oil pressure on the road was 50ish, but dropped to near zero at idle (700-800 rpm, 20-50 weight oil). 7000+ miles since a 1992 rebuild.

My engine is an early XPAG (separate oil filter), over bored to 1466 cc, unsleeved(!),with a slightly shaved head and oversized i/e valves, standard inch and a quarter SUs w/ES needles, K&N filters, static timed to 6 degrees BTDC, MGA 4.33 rear end, Vredestein 165/80/15 tires, 794 net revs per mile. I use premium gas. Fan belt loose, per Dave Dubois (tightened it a tad returning, car actually ran a little hotter). No indication of sticking brake shoes. Radiator was last hot tanked in the 70s, but had a fresh 50/50 mix w/Water Wetter. My grill slats are as wide open as possible, new water pump (last fall), MGB 7 blade plastic fan. I do, however, have a 6" Butler foglight blocking the bottom left of the radiator.

I did have one breakdown on the way down - the engine just died on I-65 in downtown Louisville - no fun! I replaced the rotor - instant startup and good running.

Upon returning home, I had to add 2 quarts of oil and a quart of coolant. After spending hours researching the archives, I enrichened each jet one flat, and checked the plugs for looseness/blowby - ok.

So, this past weekend I went to a 2 day "Motor Muster" at Greenfield Village in Dearborn, Michigan. My speed to/from never exceeded 50 mph, and the temp gauge never rose above 85 degrees, except at a couple long stoplights, then backed right down. Ambient temps were mid 80s, much more comfortable for both me and my TD.

Sorry for this wordy post - I've tried to document my TD's specifics.

Problem or paranoia? Any advice would really be greatly appreciated. Thanks!

Cliff
C A Schnell

Cliff added in another thread:
Posted 20 June 2008 at 04:21:25 UK time
C A Schnell, Michigan, USA, cschnell@sbcglobal.net
I am running with a 180-185 thermostat. It was a long time ago, but both the temp gauge and the thermostat checked out ok - hot pot of water on the stove.

Cliff

Dave Braun

Paranoia.

You won't boil a 50/50 mix at 100 C. You may want to reduce the mix to 75/25 (water/antifreeze) mix for better heat tramsfer, but you could freeze over during storage. The MGB fan is only good at very slow speeds or stopped. Air from traveling will far exceed the fan's ability at speed. The fact that you were able to drive under lower ambiant temperatures a week later says that your car is fine, but that it is up against its cooling capacity under higher ambiant temps at high speed, heavily loaded. Pushing a TD with a heavy load at 72 mph is like trying to push a barn door with a bicycle.

What does your 794 revs per mile mean? With a 4.3 (don't know of 4.33 ratio) you should be turning 17.16 mph for each 1000 rpm, so 4200 RPM is 72 mph. 60 mph is 3500 RPM, which is one mile per minute at 3500 RPM, or 3500 turns per mile.

warmly,
dave
Dave Braun

Oh, I get the 794 revs per mile now... the tires are about 80 inches in circumference, and turn 794 times in a mile... 794 turns in fourth at 4.3:1 is 3414 revs of the engine in a mile, which is close to the other calculation.

dave
Dave Braun

Cliff,

I'm intrigued about the high oil pressure, I understood that the relief spring produced a 42psi, (assuming that there aren't any washers under it!).
Quite often on these forums there are reports of high oil pressures, but my understanding is that oil pressure is needed only to overcome the effects of centrifugal force, (for example the bearings on slowly rotating bearings can be oiled by screw down grease nipples), and to lubricate the other parts of the engine. Isn't there a potential problem with sheer at high pressure?
So what are the advantages of having it so high, and how did you achieve it? I'm running at 45psi hot at 3250 and 25psi at hot idle (1000), from what I'm reading the high pressure might be too low.

Mike.


Mike Christie

Cliff,
With all of the facts that you gave, ie the ambiant temp, engine mods, speed, load, rear end ratio, etc. I believe that the engine responded exactly as it should have,,, it got hot !!! I am also assuming that the 95 degree oil pressure indication was actually where the the temp guage needle ended up in the pressure zone as it passed the 100 degree mark in the temp zone..

SPW

Steve Wincze

I would first suspect the gauge. Then the thermostat, and lastly the radiator. Re-coring my radiator made my TD run way much cooler all the time. With your mods you are putting a lot of load on the cooling system, but it should be able to handle it. Kind of suspect the oil pressure was really that high? If it was, relief valve not working (the one under the cap at bottom of the pump). George
George Butz

Yep, Steve, I missed that. I bet he meant the 95 lbs oil pressure reference was the location of the Coolant temperature needle. These things aren't very linear in that range, so it is anyones guess as to whether the temperature was over 110 C. In that case, he may bave boiled out some of his coolant (a 50/50 ethylene glycol/water mix will boil at 107 C).

George, one side problem IS the the gauge itself, it may not come back into calibration if over heated i.e. the further out from the normal operating temperature you allow the gauge to travel the more likely it will work itself out of calibration.

You know? I think if Cliff was planing to run in high ambiant temperatures with that load at that speed very often, he should consider a much more efficient radiator, either more rows, or perhaps have a deeper one fabricated from aluminum.

We used to say in business that you could have any two of having it fast, having it cheaply or having it perfect, but you couldn't have all three. Likewise, you can have any two of speed, high ambiant temp, or heavy load, but you can't have all three.

warmly,
dave
Dave Braun

I would be interested to know the max advance on your timing - you mention static timing at 6 BTDC but what is the full advance at say 3,800-4,000 RPM?

One more thing to look at I would think. With those mods, you would think it would be around 30-32 degrees max advance.

Hope you solve your problem.
Jeff
J Delk

Thank you all for your comments and concerns! I am sorry I was not more clear - Steve and Dave are correct - the temp needle climbed into the oil pressure area. I ran about 50 pounds oil pressure at speed, but, as I said it dropped to almost zero at very hot idle. I suspect that this is due to overly large rod/main bearing clearances. On my initial startup in 1992 I ran the engine for at least a minute with NO oil pressure. I deserve prison time for that mistake!

I am actually far more comfortable having read your comments. I think I was asking too much from the TD.

To Jeff D - Jeff Schlemmer rebuilt the distributor and set the advance curve based on my engine info, but I do not know at what degree full advance is or at what rpm.

I checked with a local radiator shop that has actually recored a few T radiators recently, and got a ballpark quote of $250-$350 for a recore. He said that he would have to see the radiator out of the car to determine what would cost what...

On Sunday I will be driving to/from Bay City - 130 miles or so? I plan to drain the coolant and put in straight water with Xerex radiator cleaner for the trip, then drain and flush when I get home.

Again, thank you all for your help! Please feel free to add any additional tips.

Sincerely,

Cliff
C A Schnell

This thread was discussed between 20/06/2008 and 21/06/2008

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.