[gazrnr]

I have a strange intermittent temperature spike. I am running a new GM 350 crate motor with vortec heads, performer RPM airgap intake, new radiator with shrouded electric fan, high flow water pump and all new cooling system parts. Basically everything is new. The top of the thermostat housing is slightly higher than the radiator cap. The coolant is mixed to protect to -29 on the tester.

I have about 800 miles on the motor and taken it for a few highway rides and found that cruising along in 5th at 2300 or 6th @ 1800 or so rpms the temperature will start to spike, go from 180 to 230 on the gauge then drop back down to 180 and stay there for a number of miles. The spike occurs on light throttle, not under load. At a long stop light the temp will rise and stay around 210 with the fan cycling on & off but at times I have seen it spike to 250. General driving on/off throttle the temp will stay at 180 and occasionally go up to 210 then fall back to 180. The temp sending unit in the intake near the thermostat.

The temp sensor on radiator is set to 175 to cycle the fan. When parked the gauge will show 210 and the fan will cycle on and off. Air flow to the radiator is very good and the cowl hood vents the heat very efficiently. I am not losing power or water when the temp rises. I have changed the sending unit twice and installed a new gauge with matched sending unit. I flushed the system twice, replace the thermostat twice with high flow 180's that if they stick will be in the open position. I have filled the cooling system with the the front end jacked up and cycled the air out a number of times.

Another strange occurrence it that the car seems to run warmer on the gauge when I put the heater/defroster on to draw heat off the motor. The air temp that comes out of the heater does not feel extremely hot like it would if the engine was overheating. The coolant cycles out from the intake near the thermostat thru the heater core then back to inlet on the water pump. On other cars running the defroster has helped cool a motor that was running hot. This also seems strange.

Any thoughts on what could be causing this and what the fix might be?

Thanks,
Rusty

 

[camaroman7d]

Rusty,
What type of thermostat are you running? I have had this exact same problem before. I suggest you go buy a fast acting thermostat. Either a Robert Shaw or a Mr. Gasket (they are the same). This will end your tempature spiking problem.

Royce

 

[gazrnr]

Thanks Royce,

I first used a MR Gasket 180 (Summit pn MRG-4364) and changed to a BE Cool high flow 180 (Summit pn BCI-78001).

How can I identify the fast opening thermostat? Do you know of a manufacturer part number I should look for?

Thanks,
Rusty

 

[edge]

The spike occurs on light throttle, not under load.

Maybe it is running too lean and/or too far advanced for this load condition. How to check this, I am not sure? Maybe cruise like you say and shut it down when the temp rises and check your plugs. If the plugs are bone white, you may have an area to work on.

Good luck, Ed. www.edgesz28.com

 

[gazrnr]

Thanks Ed

I am running an Edelbrock 600 cfm and jetted it 10% richer in cruse mode to see if this was it. The temperature spikes continued and performance fell off. I now have it jetted 4% richer in cruse and 2% richer in secondaries. The motor idles great, dirvabilty, WOT and fuel mileage are very good. No bog, hesitation or surge thru the rpm range.

I am running a MSD AL box and MSD pro-billet street distributor. The advance curve is matched to the specs in the owners manual and the initial timing is 12 btdc. There is no ping and the engine pulls strong. An additional 2 degrees is not the problem as I have tried running with 8, 10 & 12 degrees and still experienced the temperature spikes.

Thanks for the input.