• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Running engine hot...?

Share this page

VelodromeRacer

VelodromeRacer

Jedi Trainee
Offline
Hey all.

I am chasing an issue with the motor. I added a speedwell Alum. radiator and have a 1275 engine with 1-1/2 Su carbs.

At Mid-Ohio, I could run only a few laps and she hit 210..and spiked even higher! We retarded the timing back to 28 degrees..The plugs on the rear carb are showing way to rich as well. We did a leak down test from 100 psi and it shows 5% loss for number 1 and 2% for 2-3 and 4. I need to do something as I am set to run at Road America in under 2 weeks and this is starting to get very troubling! I run a new Distributor from APT Fast with the Petronix and I have an oil cooler. The oil at Mid Ohio during the race at 5pm last Sunday hit 230 which it never gets to. Could it be a leak in the head that opens when it gets hot? Ideas? Kent Prather did help tune the car some at Mid-Ohio and we went from BG to number 6 needles for the carbs.
 
Obviously, check the water pump belt. Even a tight one can slip if it's polished or old and hard.

Do you have a good ratio of coolant? Too much anti-freeze will make any car overheat (it doesn't reject heat as well as water).

Are you running a thermostat? I never do....just a blanking plate to add some restriction (and I make the blanking plate out of an old thermostat....just cut away the actual valve and mechanism.

Is your lower hose collapsing? The lower hose is under suction and will collapse if it becomes old. Many have a spring inside to prevent this. To check, warm up the engine and goose the gas pedal while obseving the lower hose.

Have you "burped" the coollant system to get all the air out?

Does your car have the little thermostat bypass hose? It's best to plug these off for racing (but it shouldn't make you overheat).

Sometimes the vanes on an old water pump will be worn down and corroded and won't pump enough.

You're not running an under-drive lower front pully...are you?

Pressure test the cooling system?
 
Nial,

Yes-good thoughts. More background. It is a new race motor so we went with a new water pump and I am running an oversized pulley as well. All hoses are new to. We did a pressure test of the radiator as well and had no leaks there. I have a blanking plate as well. Thinking it may be a head gasket leak? But it did pass the pressure test.

Scratching my head.....
 
You have an oversized <span style="text-decoration: underline">water pump</span> pully?
That will slow it down and might cause overheating at slower speeds (but I sort of doubt it during racing speeds unless it's a LOT oversize.

Since the radiator is apparently the recent change, I guess you should look there first. It should feel hot evenly all the way across the front.

Maybe backflush it to see if there any stuff from the welding process still in it.

If nothing else, put the old rad back in?

And yeah, it could be a head gasket opening up when warm. Torque the head and see if any seem less tight.
 
Velo--

Sorry we did not get to meet at M-O.

The leakdown numbers seem okay but was the test done with the engine cold? If so, given that this may be a problem that only shows up at temp I would warm the engine to operating temps and then do it again. Also I think you would see some evidence of leakage or blow-by when you pull the cylinder head.

Please let us know.
 
Michael,

I am sorry about that as well-I was so tied up trying to tune the Bug that I didn't get much time to wander around! I ran with group 3-as SVRA penalizes Bugeyes that run the 1275 and they do not let me run with the square bodies or other Bugeyes. Sundays final race, I did move up and ran in the 1:54 range for my laps. That was better than the 2:03 I ran at first practice.

I agree that the leakdown needs to be done with a warm engine. That is what I hope to try on Monday.

Velo
 
I used to run with no thermostat, a huge Aluminum Fluidine Radiator, 20%coolant 80%water, and a bottle of redline water wetter. At high RPM (7000-9000) I would actually drop temperature scary fast. Granted, this was on a Japanese B18C, but the idea should still hold true.
 
Back
Top