Hi all,
I just got my 1986 vert back from the shop with a new 355 mild cam engine to replace the tired original motor. I love it, it has excellent power and feels like a totally new car. My only issue is my oil temp and coolant temp are both in the 240-250 range during normal operation. The coolant temp will spike to 245, then the fan will get it back down to around 220 before it goes up again. The oil temp rises to right around 243 and stays there. We just installed a new radiator and fan last year, so I'm curious why it's running so hot. Any ideas? Thanks
P.S. I am running GTX 20W-50 as my oil

 

New engines do run hotter.

If this were my build I would also have concerns about the water temp.
Since the coolant fan will bring the temp down suggest a manual fan switch & run the engine temp on the thermostat temp at least until the engine has some miles on it.

IMHO the oil temp is ok but will no doubt run @ a lower temp if the water temp comes down.

 

Those temps seem a bit hot too me.

First thing I'd do is check the temps with a second way to see if they are accurate. Use a infrared temp gun and check the radiator and top hose. They ought to be slightly cooler or same as the the temp that is showing from the computer.

IMO with those kinds of temps you'll not be able to run "normal" timing. Probably leaving 25hp on the table because of the timing being removed.

Oil temps ought to be down in the 200-215 area after fully warmed. (like driving for 1/2hr)

 

Temps are too high for comfort, think I read over 220 oil breaks down faster(180-220 ideal for oil).

Prob should get your chip reprogramed to have the fan come on sooner and keep it down. But 1st I'd do the basic stuff and make sure air dam is good and between the radiator & ac is clear.

edit: I'd make sure they used the right rotation water pump as well and it's not running super lean.

 

I agree with all of the above but I would check the water temperature with an IR device before I did too much more. My 86 runs at 195 to 210 with a 195 thermostat. Oil runs at 235 or so.

The fan is coming on late making me think that the temperature indicator may be off. I think the fan is set to come on around 230 or so.

 

Oil temp and coolant temp should typically be within 10% of each other. The fact that your oil is close to the coolant in temperature is a good sign believe it or not.

Ok, for the basics, have you checked the coolant level? Sometimes air can hide in those systems, not always, but sometimes. It sounds as though your heat issue is pretty consistent, so I would not be surprised if the level is just fine.

I'm assuming they put on a new water pump, yes?

Do you have the specifications of the mild cam? Can you post them here?
240-245 is out of my comfort zone when it comes to operating temperature. Do you have dual electric fans? Are they original?

If memory serves, 240 is the "fail-safe" fan switch temp. Meaning if the ecm has failed to ground the fan relay and turn on the fan, then the fan switch will ground the relay instead, once a certain temperature is reached. I can't guarantee that 240 is the correct temp for the fan switch.

What I believe may be happening here is that the Ecm for whatever reason may not be turning the fan on at its appropriate temp due to bad connection, faulty ground, etc. and the fan switch is having to do the job instead.

Now, this may not be the case, but it's very easy to bump/damage wires and connectors when removing and installing an engine.

I'm assuming that the shop that did your engine has the base timing set correctly and there are no other issues. It wouldn't hurt to double check base timing before digging into wiring gremlins and the like. Hope you get it figured out.