View Full Version : New Engine Overheating

06-14-2005, 06:31 PM
Today was the second attempt at getting my new motor running for more than 30 seconds. Last weeks attempt showed my original starter to be inadequate for the tighter motor. So after replacing it with a new gear-reduction one, we gave it another go this morning. First thing to happen was the oil gauge feed tube snapped off the sending unit at the block, sending about a quart of oil onto the floor. Knowing we had good pressure, we fitted a bolt into the housing and tried again. Started right up, but it had a hard time idling so we adjusted the dual Webers until it was running smoothly. Checked the temperature gauge and it's in the red zone! Shut the motor off. After releasing the pressure through the radiator cap, we opened up the thermostat housing to find the thermostat was wide open. Stuck a meat thermometer in the opened radiator and it read 160 degrees! Now what is going on? Replaced the lost fluid and re-started the engine. Temperature gauge was now just below the red zone and it stayed there...for awhile. Then it started to climb and the meat thermometer started to climb to 170, then 180, 190...so we shut the engine down. /ubbthreads/images/graemlins/confused.gif
The only things I thought of that could be causing this are 1). a weak water pump; 2). crap from the heater core is plugging something in the system; 3). a more efficient radiator and an electric fan might help cool things down.
My plan right now is to flush the entire system and try again. But I'm really wondering what is going on here. Has anyone else ever had this type of problem before?

Geo Hahn
06-14-2005, 06:46 PM
...Started right up, but it had a hard time idling so we adjusted the dual Webers until it was running smoothly. Checked the temperature gauge and it's in the red zone!...

[/ QUOTE ]

I think I'd start by checking the gauge & sending unit. Even an engine very prone to overheating shouldn't get hot that fast. This is what I use to verify temps both at the sending unit location and around the engine:


But a pan of boiling water is about all you need to check the sender & gauge.

06-14-2005, 07:09 PM
What type of engine are you working on? Tr3?

06-14-2005, 07:39 PM
180-190 deg's is the normal operating range. A summer thermostat that is rated at 160 will start to open at that temp. Over 200 deg is where I get worried.

If the temp climbs rapidly before you can even drive a short distance at normal continuous speed , I would look for a blockage, bad radiator, def temp sensor. Assumming the water pump belt is snug & it's turning you should be able to see some circulation at the radiator with the cap off & the car mildly warm ( start the car with the cap off cold & watch ) .

Advanced timing would show up at continuous high rpm's but retarted timing would show up at idle. In either case I don't think it could raise temps enough to cause an overheating condition unless the setting was so far off , and then the car shouldn't even run.

Other things to check would be colapsed radiator hoses, bad radiator cap ( not holding pressure ), over 50% antifreeze dilution or just water, plugged or highly restricted exhaust, but again this would create a poor running motor. As you have done , confirm the actual temps with a thermometor.

Let us know what you find.

06-14-2005, 09:18 PM
I would say it took about 15-20 minutes from the time we got the TR250 engine running to when we got around to checking the temperature gauge, so it wasn't as quick as I might have led you to believe. I thought of a defective temperature sensor, because when we cracked the radiator cap and stuck the meat thermometer in there it was reading 160 degrees but the temp gauge was pinned in the red zone. After about 15-20 minutes of checking things over, scratching our heads, etc. we re-started the motor, with the thermometer still in the radiator. After about 10 minutes, I watched the thermometer go from 160 degrees to around 220 when we actually shut it down for good.
I have all new hoses, except for the hoses that feed and drain the heater core. I should also note the the coolant that spilled into the overflow bottle when we cracked the radiator cap looked dirty and the only place that could have come from is the heater core. I wanted to flush it out before getting to this point, but I'm borrowing garage space and there is no drain, nor spigot to run a hose, nearby. That's my thought: that it's being caused by crap from the heater core.
I have a new s.s. headers and exhaust system; hoses, as I said are brand new; the radiator cap I bought last Saturday; and the timing was set this morning. The radiator was new about 20,000 miles ago and during the re-build I had it stored inside a plastic garbage bag that was tied off and stored on a shelf in my cellar.
The mechanic who was with me this morning (he's the one that actually did the re-building of the motor) thinks it might be a bubble in the system and the water pump isn't efficient, or strong enough, to move it along. He thinks that because the thermostat housing sits higher than the radiator. He wants to come back when I'm ready to re-charge the coolant after flushing everything because he wants to disconnect the hose at the heater valve (the highest point) and pour the coolant in from there.
I'm at a loss as to what to do right now. I will flush the entire system first and maybe replace the sending unit. I may replace the thermostat with one that has the copper core removed, the way Kas Kastner recommends and see what that gets me.
Two questions I have right now are: Is it possible this could be a bubble within the system? and Can I test the water pump to see if it's doing it's job?

06-14-2005, 09:48 PM
The water pump is very simple in design & is rarly the cause if it's turning. The impeller is on the oposite end of the pulley shaft. I guess it's possible ( anything is ) but if the impellor came loose from the shaft you would not see lose of circulation, but again I must say it just doesn't happen. I've never seen an impellor wear out.

The second theory of an air bubble is more plausable . BMW's & others have built in air bleed ports to open and expell traped air..
If you want to get fancy you can drill & tap a bleed screw into the thermostat housing, but letting the car idle with the cap off should do it. TR's do not usually suffer from this problem.
I would do a back flush as insurance to blow out any possible debris that might be a cause. Just for the heck of it double check the gauge, if the other gauges read high the voltage stabilizer on the back of the speedo might be at fault .

New motors could run a little hotter because of tight tolerances but not to the point of overheating.

06-14-2005, 09:59 PM
Bad sealing head gasket??? Try doing a leakdown test, or get the tester to check for combustion gasses in the coolant.


06-14-2005, 10:23 PM
You might try to burp the cooling system; I used to do this in my race car by repeatedly squeezing the lower radiator hose (engine NOT running!) to push any trapped air bubbles out through the top of the radiator. Also make sure that the rad. cap is the right rating for your 250. I think it need only 7lbs but check your specs. If the heater core is suspect, just turn off the valve to eliminate it.

06-14-2005, 10:33 PM
It won't hurt to flush the cooling system and make sure there is no trapped air in the system. However, you also said you were dialing in the carbs. I know you said they are running well, but are you sure you didn't lean them way out in the process? If you're idling lean the temp will climb higher than usual. Try this at dusk and you will start seeing the exhaust glow if you're lean enough.

The Radio Shack thermometer Geo Hahn recommended is a nice tool. I got one for Christmas. Father's day is coming you know... just a thought.

06-14-2005, 11:29 PM

Flushing is probably a good idea. But, I suspect you are actually running better than you think and need to look for errors in the gauge and/or sender. Of course, keep an eye on the temps, but get the car on the road and run it gently, see what happens.

All the temps you mentioned in the first post are nothing to worry about. 160 is on the cool side, 185-200 is normal and the engine was only getting a bit hot at 220F. It's quite possible the engine only went that high because it was running for a period of time while sitting in a garage.

A freshly re-built engine is going to have more friction as the rings and bearings bed in. For that reason, many suggest getting the car on the road and moving to help keep it cooler during the first half hour of running.

It's possible from your description that your gauge or sender is out of whack, because it should show "normal" at around 185-195F. This assumes your meat thermometer is correct. You might do well to check with another meat thermometer, as well, and/or switch out the temperature sender and/or gauge.

Performance items like the Webers and the headers will add heat. Higher compression and other mods can effect this, too. Since your headers are stainless steel, you can easily warp them to significantly reduce the radiant heat coming off the pipes into the engine compartment. Wrapping also helps protect things like alternators, carbs, brake lines and starter that might be near the exhaust manifold. And, wrapping will keep the temps in the exhaust system higher, which helps move the exhaust gasses faster, making for a better breathing engine. You'd probably need to retune the carbs afterward, if you install header wrap. (Note, header wrap is not highly recommended for mild steel headers, Jet Coat or similar ceramic coatings are a better option.)

Finally, Webers really do need to be carefully tuned and the point that they might be running too lean and causing overheating is a good one (you didn't mention if they are sidedraft or downdraft Webers... sidedraft are more particular about tuning). Ideally, a dyno should be used to set up Webers initially. And, the tuning should be repeated after the engine has a couple thousand miles on it.

It doesn't sound like the water pump or thermostat are a problem.

If the engine continues to run hot, some more things to consider. During the rebuild, was the block thoroughly cleaned to remove any and all rust from the water jacket? Is there any chance some machining bits got into water passages and are partially blocking them? Hopefuly neither of these are an issue.

Some simpler things to consider. What is your coolant formula? Many use 50/50 water to anti-freeze. 75 percent water and 25 percent anti-freeze will do a lot to help the car run cooler. Also, you might want to pick up a bottle of Redline Water Wetter and add it to the system. I've used it in cars and seen it help.

An electric fan might a good idea, that can be added later. Be sure to install a good thermostat controller, to turn it on and off based on coolant temp. If you convert to a fan and remove the original one, watch out for imbalances that might effect the engine. I don't know about TR250-6, but with the 4-cylinder TRs it's critical to replace the fan and hub with a harmonic dampener. Also, electric fans tend to draw some serious amperage and might overtax your alternator, depending upon the load on it now. (I have a 14" fan in my TR4 that draws about 10 amps, had to switch from a generator to an alternator to use it, along with halogen lamps, elec. fuel pump, etc.)

Hope you get the car on the road soon!



06-15-2005, 12:37 AM
HI All, Just a quick comment, if this motor was assembled correctly why was it neccessary to get a gear reduction
starter to turn it over.???---Keoke /ubbthreads/images/graemlins/confused.gif

06-15-2005, 04:05 AM
You've been given some good advice, including about an electric fan--particularly important for idling TR engines.

I'll mention a few additional items that can be highly material to overheating in a Triumph:

a) a carburetor mixture that is too lean. Avoid this. A rich engine runs cooler. Ten degrees makes all the difference;

b) improper timing and improper advance/retard on the distributor adjustments

c) a bad radiator shroud or bad fan

It's rarely the water pump, and the air bubble should've worked itself out. Maybe not.

d) of course, a big culprit is a leaking head gasket, but if the head was properly milled and a new gasket properly installed, we'd think it's not that.

If it were me, I'd check the fuel mixture and timing. Keep tweeking the timing until it's perfect. Make sure your plugs look good, neither wet nor thick black soot. A lean mixture will show the plugs looking cooked and dry. You can find pictures online of how plugs appear with proper mixtures.

Best of luck.